Figure1_

 

 

 

Figure4_

 

     OPC UA Specification

OPC 10000-3

 

OPC Unified Architecture

Part 3: Address Space Model

 

 

Release 1.04

2017-11-22

 

 

 

 

 

 

 


 

Specification Type:

Industry Standard Specification

Comments:

Report or view errata: http://www.opcfoundation.org/errata

 

 

 

 

Document
Number

OPC 10000-3

 

 

 

Title:

OPC Unified Architecture

Part 3 :Address Space Model

Date:

2017-11-22

 

 

 

 

Version:

Release 1.04

Software:

MS-Word

 

 

Source:

OPC 10000-3 - UA Specification Part 3 - Address Space Model 1.04.docx

 

 

 

 

Author:

OPC Foundation

Status:

Release

 

 

 

 


 

 

CONTENTS

FIGURES. viii

TABLES. x

1       Scope. 1

2       Normative references. 1

3       Terms, definitions, abbreviations and conventions. 2

3.1        Terms and definitions. 2

3.2        Abbreviations. 3

3.3        Conventions. 3

3.3.1          Conventions for AddressSpace figures. 3

3.3.2          Conventions for defining NodeClasses. 4

4       AddressSpace concepts. 5

4.1        Overview. 5

4.2        Object Model 5

4.3        Node Model 5

4.3.1          General 5

4.3.2          NodeClasses. 6

4.3.3          Attributes. 6

4.3.4          References. 6

4.4        Variables. 7

4.4.1          General 7

4.4.2          Properties. 7

4.4.3          DataVariables. 7

4.5        TypeDefinitionNodes. 8

4.5.1          General 8

4.5.2          Complex TypeDefinitionNodes and their InstanceDeclarations. 8

4.5.3          Subtyping. 9

4.5.4          Instantiation of complex TypeDefinitionNodes. 9

4.6        Event Model 10

4.6.1          General 10

4.6.2          EventTypes. 11

4.6.3          Event Categorization. 11

4.7        Methods. 12

4.8        Roles. 12

4.8.1          Overview. 12

4.8.2          Well Known Roles. 12

4.8.3          Evaluating Permissions with Roles. 13

5       Standard NodeClasses. 15

5.1        Overview. 15

5.2        Base NodeClass. 15

5.2.1          General 15

5.2.2          NodeId. 16

5.2.3          NodeClass. 16

5.2.4          BrowseName. 16

5.2.5          DisplayName. 16

5.2.6          Description. 16

5.2.7          WriteMask. 16

5.2.8          UserWriteMask. 17

5.2.9          RolePermissions. 17

5.2.10        UserRolePermissions. 18

5.2.11        AccessRestrictions. 18

5.3        ReferenceType NodeClass. 18

5.3.1          General 18

5.3.2          Attributes. 19

5.3.3          References. 20

5.4        View NodeClass. 21

5.5        Objects. 23

5.5.1          Object NodeClass. 23

5.5.2          ObjectType NodeClass. 25

5.5.3          Standard ObjectType FolderType. 26

5.5.4          Client-side creation of Objects of an ObjectType. 26

5.6        Variables. 26

5.6.1          General 26

5.6.2          Variable NodeClass. 27

5.6.3          Properties. 30

5.6.4          DataVariable. 30

5.6.5          VariableType NodeClass. 31

5.6.6          Client-side creation of Variables of an VariableType. 33

5.7        Method NodeClass. 33

5.8        DataTypes. 35

5.8.1          DataType Model 35

5.8.2          Encoding Rules for different kinds of DataTypes. 36

5.8.3          DataType NodeClass. 37

5.8.4          DataTypeEncoding and Encoding Information. 39

5.9        Summary of Attributes of the NodeClasses. 40

6       Type Model for ObjectTypes and VariableTypes. 40

6.1        Overview. 40

6.2        Definitions. 40

6.2.1          InstanceDeclaration. 40

6.2.2          Instances without ModellingRules. 40

6.2.3          InstanceDeclarationHierarchy. 41

6.2.4          Similar Node of InstanceDeclaration. 41

6.2.5          BrowsePath. 41

6.2.6          Attribute Handling of InstanceDeclarations. 41

6.2.7          Attribute Handling of Variable and VariableTypes. 41

6.2.8          NodeIds of InstanceDeclarations. 41

6.3        Subtyping of ObjectTypes and VariableTypes. 41

6.3.1          Overview. 41

6.3.2          Attributes. 42

6.3.3          InstanceDeclarations. 42

6.4        Instances of ObjectTypes and VariableTypes. 45

6.4.1          Overview. 45

6.4.2          Creating an Instance. 45

6.4.3          Constraints on an Instance. 46

6.4.4          ModellingRules. 46

6.5        Changing Type Definitions that are already used. 54

7       Standard ReferenceTypes. 55

7.1        General 55

7.2        References ReferenceType. 55

7.3        HierarchicalReferences ReferenceType. 55

7.4        NonHierarchicalReferences ReferenceType. 56

7.5        HasChild ReferenceType. 56

7.6        Aggregates ReferenceType. 56

7.7        HasComponent ReferenceType. 56

7.8        HasProperty ReferenceType. 57

7.9        HasOrderedComponent ReferenceType. 57

7.10      HasSubtype ReferenceType. 57

7.11      Organizes ReferenceType. 57

7.12      HasModellingRule ReferenceType. 57

7.13      HasTypeDefinition ReferenceType. 58

7.14      HasEncoding ReferenceType. 58

7.15      GeneratesEvent 58

7.16      AlwaysGeneratesEvent 58

7.17      HasEventSource. 58

7.18      HasNotifier 59

8       Standard DataTypes. 60

8.1        General 60

8.2        NodeId. 60

8.2.1          General 60

8.2.2          NamespaceIndex. 60

8.2.3          IdentifierType. 61

8.2.4          Identifier value. 61

8.3        QualifiedName. 62

8.4        LocaleId. 62

8.5        LocalizedText 62

8.6        Argument 63

8.7        BaseDataType. 63

8.8        Boolean. 63

8.9        Byte. 63

8.10      ByteString. 63

8.11      DateTime. 63

8.12      Double. 63

8.13      Duration. 63

8.14      Enumeration. 64

8.15      Float 64

8.16      Guid. 64

8.17      SByte. 64

8.18      IdType. 64

8.19      Image. 64

8.20      ImageBMP. 64

8.21      ImageGIF. 64

8.22      ImageJPG. 64

8.23      ImagePNG. 64

8.24      Integer 64

8.25      Int16. 64

8.26      Int32. 64

8.27      Int64. 65

8.28      TimeZoneDataType. 65

8.29      NamingRuleType. 65

8.30      NodeClass. 65

8.31      Number 65

8.32      String. 65

8.33      Structure. 65

8.34      UInteger 65

8.35      UInt16. 66

8.36      UInt32. 66

8.37      UInt64. 66

8.38      UtcTime. 66

8.39      XmlElement 66

8.40      EnumValueType. 66

8.41      OptionSet 67

8.42      Union. 67

8.43      DateString. 67

8.44      DecimalString. 67

8.45      DurationString. 67

8.46      NormalizedString. 68

8.47      TimeString. 68

8.48      DataTypeDefinition. 68

8.49      StructureDefinition. 68

8.50      EnumDefinition. 69

8.51      StructureField. 69

8.52      EnumField. 70

8.53      AudioDataType. 70

8.54      Decimal 70

8.55      PermissionType. 70

8.56      AccessRestrictionsType. 71

8.57      AccessLevelType. 71

8.58      AccessLevelExType. 72

8.59      EventNotifierType. 72

8.60      AttributeWriteMask. 73

9       Standard EventTypes. 73

9.1        General 73

9.2        BaseEventType. 74

9.3        SystemEventType. 74

9.4        ProgressEventType. 74

9.5        AuditEventType. 74

9.6        AuditSecurityEventType. 76

9.7        AuditChannelEventType. 76

9.8        AuditOpenSecureChannelEventType. 76

9.9        AuditSessionEventType. 76

9.10      AuditCreateSessionEventType. 76

9.11      AuditUrlMismatchEventType. 76

9.12      AuditActivateSessionEventType. 77

9.13      AuditCancelEventType. 77

9.14      AuditCertificateEventType. 77

9.15      AuditCertificateDataMismatchEventType. 77

9.16      AuditCertificateExpiredEventType. 77

9.17      AuditCertificateInvalidEventType. 77

9.18      AuditCertificateUntrustedEventType. 77

9.19      AuditCertificateRevokedEventType. 77

9.20      AuditCertificateMismatchEventType. 77

9.21      AuditNodeManagementEventType. 77

9.22      AuditAddNodesEventType. 77

9.23      AuditDeleteNodesEventType. 78

9.24      AuditAddReferencesEventType. 78

9.25      AuditDeleteReferencesEventType. 78

9.26      AuditUpdateEventType. 78

9.27      AuditWriteUpdateEventType. 78

9.28      AuditHistoryUpdateEventType. 78

9.29      AuditUpdateMethodEventType. 78

9.30      DeviceFailureEventType. 78

9.31      SystemStatusChangeEventType. 78

9.32      ModelChangeEvents. 78

9.32.1        General 78

9.32.2        NodeVersion Property. 78

9.32.3        Views. 79

9.32.4        Event Compression. 79

9.32.5        BaseModelChangeEventType. 79

9.32.6        GeneralModelChangeEventType. 79

9.32.7        Guidelines for ModelChangeEvents. 79

9.33      SemanticChangeEventType. 80

9.33.1        General 80

9.33.2        ViewVersion and NodeVersion Properties. 80

9.33.3        Views. 80

9.33.4        Event Compression. 80

Annex A (informative)  How to use the Address Space Model 81

A.1        Overview. 81

A.2        Type definitions. 81

A.3        ObjectTypes. 81

A.4        VariableTypes. 81

A.4.1          General 81

A.4.2          Properties or DataVariables. 81

A.4.3          Many Variables and / or structured DataTypes. 82

A.5        Views. 82

A.6        Methods. 83

A.7        Defining ReferenceTypes. 83

A.8        Defining ModellingRules. 83

Annex B (informative)  OPC UA Meta Model in UML. 84

B.1        Background. 84

B.2        Notation. 84

B.3        Meta Model 85

B.3.1          Base. 85

B.3.2          ReferenceType. 86

B.3.3          Predefined ReferenceTypes. 87

B.3.4          Attributes. 87

B.3.5          Object and ObjectType. 88

B.3.6          EventNotifier 89

B.3.7          Variable and VariableType. 89

B.3.8          Method. 90

B.3.9          DataType. 91

B.3.10       View. 92

Annex C (normative)  Graphical Notation. 93

C.1        General 93

C.2        Notation. 93

C.2.1          Overview. 93

C.2.2          Simple Notation. 93

C.2.3          Extended Notation. 95

 


 

FIGURES

 

Figure 1 – AddressSpace Node diagrams................................................ 3

Figure 2 – OPC UA Object Model........................................................... 5

Figure 3 – AddressSpace Node Model..................................................... 6

Figure 4 – Reference Model.................................................................. 7

Figure 5 – Example of a Variable defined by a VariableType........................ 8

Figure 6 – Example of a Complex TypeDefinition....................................... 9

Figure 7 – Object and its Components defined by an ObjectType................ 10

Figure 8 – Permissions in the Address Space......................................... 18

Figure 9 – Symmetric and Non-Symmetric References.............................. 20

Figure 10 – Variables, VariableTypes and their DataTypes........................ 35

Figure 11 – DataType Model................................................................ 36

Figure 12 – Example of DataType Modelling........................................... 39

Figure 13 – Subtyping TypeDefinitionNodes............................................ 42

Figure 14 – The Fully-Inherited InstanceDeclarationHierarchy for BetaType.. 44

Figure 15 – An Instance and its TypeDefinitionNode................................. 45

Figure 16 – Example for several References between InstanceDeclarations.. 46

Figure 17 – Example on changing instances based on InstanceDeclarations. 48

Figure 18 – Example on changing InstanceDeclarations based  on an InstanceDeclaration........................................................................... 49

Figure 19 – Use of the Standard ModellingRule Mandatory........................ 50

Figure 20 – Example using the Standard ModellingRules Optional and Mandatory........................................................................................ 51

Figure 21 – Example on using ExposesItsArray....................................... 52

Figure 22 – Complex example on using ExposesItsArray........................... 52

Figure 23 – Example using OptionalPlaceholder with an Object and Variable 52

Figure 24 – Example using OptionalPlaceholder with a Method.................. 53

Figure 25 – Example on using MandatoryPlaceholder for Object and Variable 54

Figure 26 – Standard ReferenceType Hierarchy...................................... 55

Figure 27 – Event Reference Example................................................... 59

Figure 28 – Complex Event Reference Example...................................... 60

Figure 29 – Standard EventType Hierarchy............................................. 74

Figure 30 – Audit Behaviour of a Server................................................. 75

Figure 31 – Audit Behaviour of an Aggregating Server.............................. 76

Figure B.1 – Background of OPC UA Meta Model.................................... 84

Figure B.2 – Notation (I)..................................................................... 85

Figure B.3 – Notation (II).................................................................... 85

Figure B.4 – Base.............................................................................. 86

Figure B.5 – Reference and ReferenceType........................................... 86

Figure B.6 – Predefined ReferenceTypes............................................... 87

Figure B.7 – Attributes........................................................................ 88

Figure B.8 – Object and ObjectType...................................................... 89

Figure B.9 – EventNotifier................................................................... 89

Figure B.10 – Variable and VariableType............................................... 90

Figure B.11 – Method......................................................................... 91

Figure B.12 – DataType...................................................................... 92

Figure B.13 – View............................................................................ 92

Figure C.1 – Example of a Reference connecting two Nodes...................... 94

Figure C.2 – Example of using a TypeDefinition inside a Node................... 96

Figure C.3 – Example of exposing Attributes........................................... 96

Figure C.4 – Example of exposing Properties inline.................................. 97

 


 

TABLES

 

Table 1 – NodeClass Table Conventions................................................. 4

Table 2 – Well-Known Roles................................................................ 13

Table 3 – Example Roles.................................................................... 13

Table 4 – Example Nodes................................................................... 14

Table 5 – Example Role Assignment..................................................... 14

Table 6 – Examples of Evaluating Access.............................................. 14

Table 7 – Base NodeClass.................................................................. 15

Table 9 – ReferenceType NodeClass.................................................... 19

Table 10 – View NodeClass................................................................. 22

Table 11 – Object NodeClass.............................................................. 24

Table 12 – ObjectType NodeClass........................................................ 25

Table 13 – Variable NodeClass............................................................ 27

Table 14 – VariableType NodeClass...................................................... 32

Table 15 – Method NodeClass............................................................. 34

Table 16 – DataType NodeClass.......................................................... 38

Table 17 – Overview of Attributes......................................................... 40

Table 18 – The InstanceDeclarationHierarchy for BetaType....................... 43

Table 19 – The Fully-Inherited InstanceDeclarationHierarchy for BetaType... 43

Table 20 – Rule for ModellingRules Properties when Subtyping.................. 47

Table 21 – Properties of ModellingRules................................................ 49

Table 22 – NodeId Definition............................................................... 60

Table 23 – IdentifierType Values.......................................................... 61

Table 24 – NodeId Null Values............................................................. 61

Table 25 – QualifiedName Definition..................................................... 62

Table 26 – LocaleId Examples............................................................. 62

Table 27 – LocalizedText Definition....................................................... 62

Table 28 – Argument Definition............................................................ 63

Table 29 – TimeZoneDataType Definition............................................... 65

Table 30 – NamingRuleType Values...................................................... 65

Table 31 – NodeClass Values.............................................................. 65

Table 32 – EnumValueType Definition................................................... 66

Table 33 – OptionSet Definition............................................................ 67

Table 34 – StructureDefinition Structure................................................. 69

Table 35 – EnumDefinition Structure..................................................... 69

Table 36 – StructureField Structure....................................................... 69

Table 37 – EnumField Structure........................................................... 70

Table 38 – PermissionType Definition.................................................... 70

Table 39 – AccessRestrictionsType Definition......................................... 71

Table 40 – AccessLevelType Definition.................................................. 72

Table 41 – AccessLevelExType Definition.............................................. 72

Table 42 – EventNotifierType Definition................................................. 73

Table 43 – Bit mask for WriteMask and UserWriteMask............................ 73

Table C.1 – Notation of Nodes depending on the NodeClass...................... 94

Table C.2 – Simple Notation of Nodes depending on the NodeClass............ 95

 


OPC Foundation

____________

 

UNIFIED ARCHITECTURE –

FOREWORD

This specification is the specification for developers of OPC UA applications. The specification is a result of an analysis and design process to develop a standard interface to facilitate the development of applications by multiple vendors that shall inter-operate seamlessly together.

Copyright © 2006-2018, OPC Foundation, Inc.

AGREEMENT OF USE

COPYRIGHT RESTRICTIONS

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OPC Foundation members and non-members are prohibited from copying and redistributing this specification. All copies must be obtained on an individual basis, directly from the OPC Foundation Web site
HTUhttp://www.opcfoundation.orgUTH.

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The attention of adopters is directed to the possibility that compliance with or adoption of OPC specifications may require use of an invention covered by patent rights. OPC shall not be responsible for identifying patents for which a license may be required by any OPC specification, or for conducting legal inquiries into the legal validity or scope of those patents that are brought to its attention. OPC specifications are prospective and advisory only. Prospective users are responsible for protecting themselves against liability for infringement of patents.

WARRANTY AND LIABILITY DISCLAIMERS

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COMPLIANCE

The OPC Foundation shall at all times be the sole entity that may authorize developers, suppliers and sellers of hardware and software to use certification marks, trademarks or other special designations to indicate compliance with these materials. Products developed using this specification may claim compliance or conformance with this specification if and only if the software satisfactorily meets the certification requirements set by the OPC Foundation. Products that do not meet these requirements may claim only that the product was based on this specification and must not claim compliance or conformance with this specification.

Trademarks

Most computer and software brand names have trademarks or registered trademarks. The individual trademarks have not been listed here.

GENERAL PROVISIONS

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This Agreement shall be governed by and construed under the laws of the State of Minnesota, excluding its choice or law rules.

This Agreement embodies the entire understanding between the parties with respect to, and supersedes any prior understanding or agreement (oral or written) relating to, this specification.

ISSUE REPORTING

The OPC Foundation strives to maintain the highest quality standards for its published specifications, hence they undergo constant review and refinement. Readers are encouraged to report any issues and view any existing errata here: HTUhttp://www.opcfoundation.org/errataUTH

 


Revision 1.04 Highlights

The following table includes the Mantis issues resolved with this revision.

Mantis ID

Summary

Resolution

3163

Reference broken

In section 8.22 the reference to spec was fixed.

3127

Element order of LocalizedText different from Part 6

Changed order in 8.5 from text / locale to locale / text to match Part 6 and implementations

3018

Handling of DataType Encoding Information

Added Property to DataType NodeClass in 5.8.3 containing information about data type definition. Added DataTypes for handling the information in 8.48, 8.49, 8.50, 8.51, and 8.52.

Removed the old approach having DataTypeDictionaries. This effects 5.6.2, where Properties have been removed, 5.8, where the old approach was defined in detail, and 5.5.1 as well as 7, where the ReferenceType HasDefinition and its usage was removed.

The old approach is moved to an annex of Part 5 and can still be applied by OPC UA Applications.

3243

Clarification on SemanticChange bit

Changed description in 5.6.2 explaining that SemanticChange bit also requires triggering SementicsChanged bit in subscription and does not have to be set if Property cannot change.

3535

Need attribute to indicate atomicity

Added a new Attribute AccessLevelEx which contains a bits to indicate atomic access capability in 5.6.2

3306

Clarification of Server and Source Time stamps

Added clarifying text to section 8.38

3161,

3181

Clarification of OptionSet Value and ValueBits

Added clarifying text to Table 33 and 8.52

3681

User Authentication Addition

Added Roles sections 4.8, 5.2.9,5.2.10 and 5.2.11

3416

Instance declaration nodes can have an abstract type

Added clarifying text to section 6.2.1

2994

2995

Meta data to indicate encryption is required

Added AccessRestrictions Attribute

3536

No access level flag for optional IndexRange write

Added a new Attribute AccessLevelEx which contains a bit to indicate array index range write capability in 5.6.2

3676

AccessRestrictions requires “Session required” flag

Added a new flag “SessionRequired” to AccessRestrictions in 5.2.11

3652

Audio Data Type for Part 9

Added new DataType AudioDataType in 8.53

3504

AccessLevel StatusWrite bit

Clarifying text added in 5.6.2

3511

Subtyping Unions needs clarification

Clarifying text added in 8.42

3722

Decimal DataType

Added new DataType Decimal in 8.54

3602

UserAccess, UserExecutable and UserWriteMask clarification

Added clarification text to 5.2.8, 5.6.2 and 5.7.

3665

Application of Modelling rules for Methods

Added text to OptionalPlaceholder 6.4.4.5.5 and ManditoryPlaceholder 6.4.4.5.6 modelling rules describing their use with Methods.

3797

MaxStringLength

Added clarification text to 5.6.4.

3818

ValueAsText applicability

Added clarification text to Table 13

3827

BrowseNames for component variables for structures

Added BrowseName description to 5.6.4

3888

Array Dimensions for StructureField fields

Added arrayDimensions to StructureField Table 36

3923

ArrayDimensions description does not have meaning

Added clarification of ArrayDImensions in Variable NodeClass Table 13, VariableType NodeClass Table 14. Added arrayDimensions in Argument DataType Table 28

 

 


OPC Unified Architecture Specification

 

Part 3: Address Space Model

 

 

 

1    Scope

This specification describes the OPC Unified Architecture (OPC UA) AddressSpace and its Objects. This Part is the OPC UA meta model on which OPC UA information models are based.

2    Normative references

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments and errata) applies.

OPC 10000-1, OPC Unified Architecture - Part 1: Overview and Concepts

http://www.opcfoundation.org/UA/Part1/

OPC 10000-2, OPC Unified Architecture - Part 2: Security Model

http://www.opcfoundation.org/UA/Part2/

OPC 10000-4, OPC Unified Architecture - Part 4: Services

http://www.opcfoundation.org/UA/Part4/

OPC 10000-5, OPC Unified Architecture - Part 5: Information Model

http://www.opcfoundation.org/UA/Part5/

OPC 10000-6, OPC Unified Architecture - Part 6: Mappings

http://www.opcfoundation.org/UA/Part6/

OPC 10000-8, OPC Unified Architecture - Part 8: Data Access

http://www.opcfoundation.org/UA/Part8/

OPC 10000-9, OPC Unified Architecture - Part 9: Alarms and Conditions

http://www.opcfoundation.org/UA/Part9/

OPC 10000-11, OPC Unified Architecture - Part 11: Historical Access

http://www.opcfoundation.org/UA/Part11/

ISO/IEC 10918-1: Information technology – Digital compression and coding of continuous-tone still images: Requirements and guidelines

https://www.iso.org/standard/18902.html

ISO/IEC 15948: Information technology – Computer graphics and image processing – Portable Network Graphics (PNG): Functional specification

https://www.iso.org/standard/29581.html

ISO 639 (all parts): Codes for the representation of names of languages

https://www.iso.org/iso-639-language-codes.html

ISO 3166 (all parts): Codes for the representation of names of countries and their subdivisions

https://www.iso.org/iso-3166-country-codes.html

ISO/IEC/IEEE 60559:2011: Information technology – Microprocessor Systems – Floating-Point arithmetic

 https://www.iso.org/standard/57469.html

IETF RFC 5646: Tags for Identifying Languages

http://tools.ietf.org/html/rfc5646

ISO 8601-2000: Data elements and interchange formats

https://www.iso.org/standard/26780.html

Unicode Annex15: Unicode Standard Annex #15: Unicode Normalization Forms

http://www.unicode.org/reports/tr15/

W3C XML Schema Definition Language (XSD) Part 2: DataTypes

http://www.w3.org/TR/xmlschema-2/

TAI: International Atomic Time

http://www.bipm.org/en/bipm-services/timescales/tai.html

3    Terms, definitions, abbreviations and conventions

3.1    Terms and definitions

For the purposes of this document, the terms and definitions given in The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments and errata) applies.

OPC 10000-1 as well as the following apply.

3.1.1    

DataType

instance of a DataType Node that is used together with the ValueRank Attribute to define the data type of a Variable

3.1.2    

DataTypeId

NodeId of a DataType Node

3.1.3    

DataVariable

Variables that represent values of Objects, either directly or indirectly for complex Variables, where the Variables are always the TargetNode of a HasComponent Reference

3.1.4    

EventType

ObjectType Node that represents the type definition of an Event

3.1.5    

Hierarchical Reference

Reference that is used to construct hierarchies in the AddressSpace

Note 1 to entry: All hierarchical ReferenceTypes are derived from HierarchicalReferences.

3.1.6    

InstanceDeclaration

Node that is used by a complex TypeDefinitionNode to expose its complex structure

Note 1 to entry: It is an instance used by a type definition.

3.1.7    

ModellingRule

metadata of an InstanceDeclaration that defines how the InstanceDeclaration will be used for instantiation and also defines subtyping rules for an InstanceDeclaration

3.1.8    

Property

Variables that are the TargetNode for a HasProperty Reference

Note 1 to entry: Properties describe the characteristics of a Node.

3.1.9    

SourceNode

Node having a Reference to another Node

EXAMPLE: In the Reference “A contains B”, “A” is the SourceNode.

3.1.10    

TargetNode

Node that is referenced by another Node

EXAMPLE: In the Reference “A Contains B”, “B” is the TargetNode.

3.1.11    

TypeDefinitionNode

Node that is used to define the type of another Node

Note 1 to entry: ObjectType and VariableType Nodes are TypeDefinitionNodes.

3.1.12    

VariableType

Node that represents the type definition for a Variable

3.2    Abbreviations

UA        Unified Architecture

UML      Unified Modeling Language

URI       Uniform Resource Identifier

W3C     World Wide Web Consortium

XML      Extensible Markup Language

3.3    Conventions

3.3.1   Conventions for AddressSpace figures

Nodes and their References to each other are illustrated using figures. Figure 1 illustrates the conventions used in these figures.

Figure5_

Figure 1AddressSpace Node diagrams

In these figures, rectangles represent Nodes. Node rectangles may be titled with one or two lines of text. When two lines are used, the first text line in the rectangle identifies the NodeClass and the second line contains the BrowseName. When one line is used, it contains the BrowseName.

Node rectangles may contain boxes used to define their Attributes and References. Specific names in these boxes identify specific Attributes and References.

Shaded rectangles with rounded corners and with arrows passing through them represent References. The arrow that passes through them begins at the SourceNode and points to the TargetNode. References may also be shown by drawing an arrow that starts at the Reference name in the “References” box and ends at the TargetNode.

3.3.2   Conventions for defining NodeClasses

Clause 5 defines AddressSpace NodeClasses. Table 1 describes the format of the tables used to define NodeClasses.

Table 1 – NodeClass Table Conventions

Name

Use

Data Type

Description

Attributes

 

 

 

    “Attribute name”

“M” or “O”

Data type of the Attribute

Defines the Attribute

 

 

 

 

References

 

 

 

    “Reference name”

“1”, “0..1” or “0..*”

Not used

Describes the use of the Reference by the NodeClass

 

 

 

 

Standard Properties

 

 

 

    “Property name”

“M” or “O”

Data type of the Property

Defines the Property

 

The Name column contains the name of the Attribute, the name of the ReferenceType used to create a Reference or the name of a Property referenced using the HasProperty Reference.

The Use column defines whether the Attribute or Property is mandatory (M) or optional (O). When mandatory the Attribute or Property shall exist for every Node of the NodeClass. For References it specifies the cardinality. The following values may apply:

·     “0..*” identifies that there are no restrictions, that is, the Reference does not have to be provided but there is no limitation how often it can be provided;

·     “0..1” identifies that the Reference is provided at most once;

·     “1” identifies that the Reference shall be provided exactly once.

The Data Type column contains the name of the DataType of the Attribute or Property. It is not used for References.

The Description column contains the description of the Attribute, the Reference or the Property.

Only this standard may define Attributes. Thus, all Attributes of the NodeClass are specified in the table and can only be extended by other parts of this series of standards.

This standard also defines ReferenceTypes, but ReferenceTypes can also be specified by a Server or by a client using the NodeManagement Services specified in OPC 10000-4. Thus, the NodeClass tables contained in this standard can contain the base ReferenceType called References identifying that any ReferenceType may be used for the NodeClass, including system specific ReferenceTypes. The NodeClass tables only specify how the NodeClasses can be used as SourceNodes of References, not as TargetNodes. If a NodeClass table allows a ReferenceType for its NodeClass to be used as SourceNode, this is also true for subtypes of the ReferenceType. However, subtypes of the ReferenceType may restrict its SourceNodes.

This standard defines Properties, but Properties can be defined by other standard organizations or vendors and Nodes can have Properties that are not standardised. Properties defined in this standard are defined by their name, which is mapped to the BrowseName having the NamespaceIndex 0, which represents the Namespace for OPC UA.

The Use column (optional or mandatory) does not imply a specific ModellingRule for Properties. Different Server implementations will choose to use ModellingRules appropriate for them.

4    AddressSpace concepts

4.1    Overview

The remainder of 4 defines the concepts of the AddressSpace. Clause 5 defines the NodeClasses of the AddressSpace representing the AddressSpace concepts. Clause 6 defines details on the type model for ObjectTypes and VariableTypes. Standard ReferenceTypes, DataTypes and EventTypes are defined in Clauses 7 to 9.

The informative Annex A describes general considerations on how to use the Address Space Model and the informative Annex B provides a UML Model of the Address Space Model. The normative Annex C defines a graphical notation for OPC UA data.

4.2    Object Model

The primary objective of the OPC UA AddressSpace is to provide a standard way for Servers to represent Objects to Clients. The OPC UA Object Model has been designed to meet this objective. It defines Objects in terms of Variables and Methods. It also allows relationships to other Objects to be expressed. Figure 2 illustrates the model.

Figure6_

Figure 2 – OPC UA Object Model

The elements of this model are represented in the AddressSpace as Nodes. Each Node is assigned to a NodeClass and each NodeClass represents a different element of the Object Model. Clause 5 defines the NodeClasses used to represent this model.

4.3    Node Model

4.3.1   General

The set of Objects and related information that the OPC UA Server makes available to Clients is referred to as its AddressSpace. The model for Objects is defined by the OPC UA Object Model (see 4.2).

Objects and their components are represented in the AddressSpace as a set of Nodes described by Attributes and interconnected by References. Figure 3 illustrates the model of a Node and the remainder of 4.3 discusses the details of the Node Model.

Figure7_

Figure 3 – AddressSpace Node Model

4.3.2   NodeClasses

NodeClasses are defined in terms of the Attributes and References that shall be instantiated (given values) when a Node is defined in the AddressSpace. Attributes are discussed in 4.3.3 and References in 4.3.4.

Clause 5 defines the NodeClasses for the OPC UA AddressSpace. These NodeClasses are referred to collectively as the metadata for the AddressSpace. Each Node in the AddressSpace is an instance of one of these NodeClasses. No other NodeClasses shall be used to define Nodes, and as a result, Clients and Servers are not allowed to define NodeClasses or extend the definitions of these NodeClasses.

4.3.3   Attributes

Attributes are data elements that describe Nodes. Clients can access Attribute values using Read, Write, Query, and Subscription/MonitoredItem Services. These Services are defined in OPC 10000-4.

Attributes are elementary components of NodeClasses. Attribute definitions are included as part of the NodeClass definitions in Clause 5 and, therefore, are not included in the AddressSpace.

Each Attribute definition consists of an attribute id (for attribute ids of Attributes, see OPC 10000-6), a name, a description, a data type and a mandatory/optional indicator. The set of Attributes defined for each NodeClass shall not be extended by Clients or Servers.

When a Node is instantiated in the AddressSpace, the values of the NodeClass Attributes are provided. The mandatory/optional indicator for the Attribute indicates whether the Attribute has to be instantiated.

4.3.4   References

References are used to relate Nodes to each other. They can be accessed using the browsing and querying Services defined in OPC 10000-4.

Like Attributes, they are defined as fundamental components of Nodes. Unlike Attributes, References are defined as instances of ReferenceType Nodes. ReferenceType Nodes are visible in the AddressSpace and are defined using the ReferenceType NodeClass (see 5.3).

The Node that contains the Reference is referred to as the SourceNode and the Node that is referenced is referred to as the TargetNode. The combination of the SourceNode, the ReferenceType and the TargetNode are used in OPC UA Services to uniquely identify References. Thus, each Node can reference another Node with the same ReferenceType only once. Any subtypes of concrete ReferenceTypes are considered to be equal to the base concrete ReferenceTypes when identifying References (see 5.3 for subtypes of ReferenceTypes). Figure 4 illustrates this model of a Reference.

Figure8_

Figure 4 – Reference Model

The TargetNode of a Reference may be in the same AddressSpace or in the AddressSpace of another OPC UA Server. TargetNodes located in other Servers are identified in OPC UA Services using a combination of the remote Server name and the identifier assigned to the Node by the remote Server.

OPC UA does not require that the TargetNode exists, thus References may point to a Node that does not exist.

4.4    Variables

4.4.1   General

Variables are used to represent values. Two types of Variables are defined, Properties and DataVariables. They differ in the kind of data that they represent and whether they can contain other Variables.

4.4.2   Properties

Properties are Server-defined characteristics of Objects, DataVariables and other Nodes. Properties differ from Attributes in that they characterise what the Node represents, such as a device or a purchase order. Attributes define additional metadata that is instantiated for all Nodes from a NodeClass. Attributes are common to all Nodes of a NodeClass and only defined by this specification whereas Properties can be Server-defined.

For example, an Attribute defines the DataType of Variables whereas a Property can be used to specify the engineering unit of some Variables.

To prevent recursion, Properties are not allowed to have Properties defined for them. To easily identify Properties, the BrowseName of a Property shall be unique in the context of the Node containing the Properties (see 5.6.3 for details).

A Node and its Properties shall always reside in the same Server.

4.4.3   DataVariables

DataVariables represent the content of an Object. For example, a file Object may be defined that contains a stream of bytes. The stream of bytes may be defined as a DataVariable that is an array of bytes. Properties may be used to expose the creation time and owner of the file Object.

For example, if a DataVariable is defined by a data structure that contains two fields, “startTime” and “endTime” then it might have a Property specific to that data structure, such as “earliestStartTime”.

As another example, function blocks in control systems might be represented as Objects. The parameters of the function block, such as its setpoints, may be represented as DataVariables. The function block Object might also have Properties that describe its execution time and its type.

DataVariables may have additional DataVariables, but only if they are complex. In this case, their DataVariables shall always be elements of their complex definitions. Following the example introduced by the description of Properties in 4.4.2, the Server could expose “startTime” and “endTime” as separate components of the data structure.

As another example, a complex DataVariable may define an aggregate of temperature values generated by three separate temperature transmitters that are also visible in the AddressSpace. In this case, this complex DataVariable could define HasComponent References from it to the individual temperature values that it is composed of.

4.5    TypeDefinitionNodes

4.5.1   General

OPC UA Servers shall provide type definitions for Objects and Variables. The HasTypeDefinition Reference shall be used to link an instance with its type definition represented by a TypeDefinitionNode. Type definitions are required; however, OPC 10000-5 defines a BaseObjectType, a PropertyType, and a BaseDataVariableType so a Server can use such a base type if no more specialised type information is available. Objects and Variables inherit the Attributes specified by their TypeDefinitionNode (see 6.4 for details).

In some cases, the NodeId used by the HasTypeDefinition Reference will be well-known to Clients and Servers. Organizations may define TypeDefinitionNodes that are well-known in the industry. Well-known NodeIds of TypeDefinitionNodes provide for commonality across OPC UA Servers and allow Clients to interpret the TypeDefinitionNode without having to read it from the Server. Therefore, Servers may use well-known NodeIds without representing the corresponding TypeDefinitionNodes in their AddressSpace. However, the TypeDefinition­Nodes shall be provided for generic Clients. These TypeDefinitionNodes may exist in another Server.

The following example, illustrated in Figure 5, describes the use of the HasTypeDefinition Reference. In this example, a setpoint parameter “SP” is represented as a DataVariable in the AddressSpace. This DataVariable is part of an Object not shown in the figure.

To provide for a common setpoint definition that can be used by other Objects, a specialised VariableType is used. Each setpoint DataVariable that uses this common definition will have a HasTypeDefinition Reference that identifies the common “SetPoint” VariableType.

Figure9_

Figure 5 – Example of a Variable defined by a VariableType

4.5.2   Complex TypeDefinitionNodes and their InstanceDeclarations

TypeDefinitionNodes can be complex. A complex TypeDefinitionNode also defines References to other Nodes as part of the type definition. The ModellingRules defined in 6.4.4 specify how those Nodes are handled when creating an instance of the type definition.

A TypeDefinitionNode references instances instead of other TypeDefinitionNodes to allow unique names for several instances of the same type, to define default values and to add References for those instances that are specific to this complex TypeDefinitionNode and not to the TypeDefinitionNode of the instance. For example, in Figure 6 the ObjectType “AI_BLK_TYPE”, representing a function block, has a HasComponent Reference to a Variable “SP” of the VariableType “SetPoint”. “AI_BLK_TYPE” could have an additional setpoint Variable of the same type using a different name. It could add a Property to the Variable that was not defined by its TypeDefinitionNode “SetPoint”. And it could define a default value for “SP”, that is, each instance of “AI_BLK_TYPE” would have a Variable “SP” initially set to this value.

Figure10_

Figure 6 – Example of a Complex TypeDefinition

This approach is commonly used in object-oriented programming languages in which the variables of a class are defined as instances of other classes. When the class is instantiated, each variable is also instantiated, but with the default values (constructor values) defined for the containing class. That is, typically, the constructor for the component class runs first, followed by the constructor for the containing class. The constructor for the containing class may override component values set by the component class.

To distinguish instances used for the type definitions from instances that represent real data, those instances are called InstanceDeclarations. However, this term is used to simplify this specification, if an instance is an InstanceDeclaration or not is only visible in the AddressSpace by following its References. Some instances may be shared and therefore referenced by TypeDefinitionNodes, InstanceDeclarations and instances. This is similar to class variables in object-oriented programming languages.

4.5.3   Subtyping

This standard allows subtyping of type definitions. The subtyping rules are defined in Clause 6. Subtyping of ObjectTypes and VariableTypes allows:

·     Clients that only know the supertype to handle an instance of the subtype as if it were an instance of the supertype;

·     instances of the supertype to be replaced by instances of the subtype;

·     specialised types that inherit common characteristics of the base type.

In other words, subtypes reflect the structure defined by their supertype but may add additional characteristics. For example, a vendor may wish to extend a general “TemperatureSensor” VariableType by adding a Property providing the next maintenance interval. The vendor would do this by creating a new VariableType which is a TargetNode for a HasSubtype reference from the original VariableType and adding the new Property to it.

4.5.4   Instantiation of complex TypeDefinitionNodes

The instantiation of complex TypeDefinitionNodes depends on the ModellingRules defined in 6.4.4. However, the intention is that instances of a type definition will reflect the structure defined by the TypeDefinitionNode. Figure 7 shows an instance of the TypeDefinitionNode “AI_BLK_TYPE”, where the ModellingRule Mandatory, defined in 6.4.4.5.2, was applied for its containing Variable. Thus, an instance of “AI_BLK_TYPE”, called AI_BLK_1”, has a HasTypeDefinition Reference to “AI_BLK_TYPE”. It also contains a Variable “SP” having the same BrowseName as the Variable “SP” used by the TypeDefinitionNode and thereby reflects the structure defined by the TypeDefinitionNode.

Figure11_

Figure 7 – Object and its Components defined by an ObjectType

A client knowing the ObjectType “AI_BLK_TYPE” can use this knowledge to directly browse to the containing Nodes for each instance of this type. This allows programming against the TypeDefinitionNode. For example, a graphical element may be programmed in the client that handles all instances of “AI_BLK_TYPE” in the same way by showing the value of “SP”.

There are several constraints related to programming against the TypeDefinitionNode. A TypeDefinitionNode or an InstanceDeclaration shall never reference two Nodes having the same BrowseName using forward hierarchical References. Instances based on InstanceDeclarations shall always keep the same BrowseName as the InstanceDeclaration they are derived from. A special Service defined in OPC 10000-4 called TranslateBrowsePathsToNodeIds may be used to identify the instances based on the InstanceDeclarations. Using the simple Browse Service might not be sufficient since the uniqueness of the BrowseName is only required for TypeDefinitionNodes and InstanceDeclarations, not for other instances. Thus, “AI_BLK_1” may have another Variable with the BrowseName “SP”, although this one would not be derived from an InstanceDeclaration of the TypeDefinitionNode.

Instances derived from an InstanceDeclaration shall be of the same TypeDefinitionNode or a subtype of this TypeDefinitionNode.

A TypeDefinitionNode and its InstanceDeclarations shall always reside in the same Server. However, instances may point with their HasTypeDefinition Reference to a TypeDefinitionNode in a different Server.

4.6    Event Model

4.6.1   General

The Event Model defines a general purpose eventing system that can be used in many diverse vertical markets.

Events represent specific transient occurrences. System configuration changes and system errors are examples of Events. Event Notifications report the occurrence of an Event. Events defined in this document are not directly visible in the OPC UA AddressSpace. Objects and Views can be used to subscribe to Events. The EventNotifier Attribute of those Nodes identifies if the Node allows subscribing to Events. Clients subscribe to such Nodes to receive Notifications of Event occurrences.

Event Subscriptions use the Monitoring and Subscription Services defined in OPC 10000-4 to subscribe to the Event Notifications of a Node.

Any OPC UA Server that supports eventing shall expose at least one Node as EventNotifier. The Server Object defined in OPC 10000-5 is used for this purpose. Events generated by the Server are available via this Server Object. A Server is not expected to produce Events if the connection to the event source is down for some reason (i.e. the system is offline).

Events may also be exposed through other Nodes anywhere in the AddressSpace. These Nodes (identified via the EventNotifier Attribute) provide some subset of the Events generated by the Server. The position in the AddressSpace dictates what this subset will be. For example, a process area Object representing a functional area of the process would provide Events originating from that area of the process only. It should be noted that this is only an example and it is fully up to the Server to determine what Events should be provided by which Node.

4.6.2   EventTypes

Each Event is of a specific EventType. A Server may support many types. This part defines the BaseEventType that all other EventTypes derive from. It is expected that other companion specifications will define additional EventTypes deriving from the base types defined in this part.

The EventTypes supported by a Server are exposed in the AddressSpace of a Server. EventTypes are represented as ObjectTypes in the AddressSpace and do not have a special NodeClass associated to them. OPC 10000-5 defines how a Server exposes the EventTypes in detail.

EventTypes defined in this document are specified as abstract and therefore never instantiated in the AddressSpace. Event occurrences of those EventTypes are only exposed via a Subscription. EventTypes exist in the AddressSpace to allow Clients to discover the EventType. This information is used by a client when establishing and working with Event Subscriptions. EventTypes defined by other parts of this series of standards or companion specifications as well as Server specific EventTypes may be defined as not abstract and therefore instances of those EventTypes may be visible in the AddressSpace although Events of those EventTypes are also accessible via the Event Notification mechanisms.

Standard EventTypes are described in Clause 9. Their representation in the AddressSpace is specified in OPC 10000-5.

4.6.3   Event Categorization

Events can be categorised by creating new EventTypes which are subtypes of existing EventTypes but do not extend an existing type. They are used only to identify an event as being of the new EventType. For example, the EventType DeviceFailureEventType could be subtyped into TransmitterFailureEventType and ComputerFailureEventType. These new subtypes would not add new Properties or change the semantic inherited from the DeviceFailureEventType other than purely for categorization of the Events.

Event sources can also be organised into groups by using the Event ReferenceTypes described in 7.16 and 7.18. For example, a Server may define Objects in the AddressSpace representing Events related to physical devices, or Event areas of a plant or functionality contained in the Server. Event References would be used to indicate which Event sources represent physical devices and which ones represent some Server-based functionality. In addition, References can be used to group the physical devices or Server-based functionality into hierarchical Event areas. In some cases, an Event source may be categorised as being both a device and a Server function. In this case, two relationships would be established. Refer to the description of the Event ReferenceTypes for additional examples.

Clients can select a category or categories of Events by defining content filters that include terms specifying the EventType of the Event or a grouping of Event sources. The two mechanisms allow for a single Event to be categorised in multiple manners. A client could obtain all Events related to a physical device or all failures of a particular device.

4.7    Methods

Methods are “lightweight” functions, whose scope is bounded by an owning (see Note) Object, similar to the methods of a class in object-oriented programming or an owning ObjectType, similar to static methods of a class. Methods are invoked by a client, proceed to completion on the Server and return the result to the client. The lifetime of the Method’s invocation instance begins when the client calls the Method and ends when the result is returned.

NOTEThe owning Object or ObjectType is specified in the service call when invoking the Method.

While Methods may affect the state of the owning Object, they have no explicit state of their own. In this sense, they are stateless. Methods can have a varying number of input arguments and return resultant arguments. Each Method is described by a Node of the Method NodeClass. This Node contains the metadata that identifies the Method’s arguments and describes its behaviour.

Methods are invoked by using the Call Service defined in OPC 10000-4.

Clients discover the Methods supported by a Server by browsing for the owning Objects References that identify their supported Methods.

4.8    Roles

4.8.1   Overview

A Role is a function assumed by a Client when it accesses a Server. Roles are used to separate authentication (determining who a Client is) from authorization (determining what the Client is allowed to do). By separating these tasks Servers can allow centralized services to manage user identities and credentials while the Server only manages the Permissions on its Nodes assigned to Roles.

The set of Roles supported by a Server are published as components of the Roles Object defined in OPC 10000-5. Servers should define a base set of Roles and allow configuration Clients to add system specific Roles

When a Session is created, the Server must determine what Roles are granted to that Session. This specification defines standard mapping rules which Servers may support. Servers may also use vendor specific mapping rules in addition to or instead of the standard rules.

The standard mapping rules allow Roles to be granted based on:

·      User identity;

·      Application identity;

·      Endpoint;

User identity mappings can be based on user names, user certificates or user groups. Well known groups include ‘AuthenticatedUser’ (any user with valid credentials) and ‘Anonymous’ (no user credentials provided).

Application identity mappings are based on the ApplicationUri specified in the Client Certificate. Application identity can only be enforced if the Client proves possession of a trusted Certificate by using it to create a Secure Channel or by providing a signature in ActivateSession (see OPC 10000-4).

Endpoint identity mappings are based on the URL used to connect to the Server. Endpoint identity can be used to restrict access to Clients running on particular networks.

OPC 10000-5 defines the Objects, Methods and DataTypes used to represent and manage these mapping rules in the Address Space.

4.8.2   Well Known Roles

All Servers should support the well-known Roles which are defined in Table 2. The NodeIds for the well-known Roles are defined in OPC 10000-6.

 Table 2 – Well-Known Roles

BrowseName

Suggested Permissions

Anonymous

The Role has very limited access for use when a Session has anonymous credentials.

AuthenticatedUser

The Role has limited access for use when a Session has valid non-anonymous credentials but has not been explicitly granted access to a Role.

Observer

The Role is allowed to browse, read live data, read historical data/events or subscribe to data/events.

Operator

The Role is allowed to browse, read live data, read historical data/events or subscribe to data/events.

In addition, the Session is allowed to write some live data and call some Methods.

Engineer

The Role is allowed to browse, read/write configuration data, read historical data/events, call Methods or subscribe to data/events.

Supervisor

The Role is allowed to browse, read live data, read historical data/events, call Methods or subscribe to data/events.

ConfigureAdmin

The Role is allowed to change the non-security related configuration settings.

SecurityAdmin

The Role is allowed to change security related settings.

 

4.8.3   Evaluating Permissions with Roles

When a Client attempts to access a Node, the Server goes through the list of Roles granted to the Session and logically ORs the Permissions for the Role on the Node. If there are no Node specific Permissions then the default Permissions for the Role in the DefaultRolePermissions Property of the NamespaceMetadata for the namespace the Node belongs to are used (see OPC 10000-5). The resulting mask is the effective Permissions. If the bits corresponding to current operation are set, then the operation can proceed. If they are not set the Server returns Bad_UserAccessDenied.

Roles appear under the Roles Object in the Server Address Space. Each Role has mapping rules defined which appear as Properties of the Role Object (see OPC 10000-5). The examples shown in Table 3 illustrate how the standard mapping rules can be used to determine which Roles a Session has access to and, consequently, the Permissions that are granted to the Session.

 Table 3 – Example Roles

Role

Mapping Rules

Description

Anonymous

Identities =  Anonymous

Applications =

Endpoints =

An identity mapping rule that specifies the Role applies to anonymous users.

AuthenticatedUser

Identities = AuthenticatedUser

Applications =

Endpoints =

An identity mapping rule that specifies the Role applies to authenticated users.

Operator1

Identities = User with name ‘Joe’

Applications = urn:OperatorStation1

Endpoints =

An identity mapping rule that specifies specific users that have access to the Role with a application rule that restricts access to a single Client application.

Operator2

Identities = Users with name ‘Joe’ or ‘Ann’

Applications = urn:OperatorStation2

Endpoints =

An identity mapping rule that specifies specific users that have access to the Role with a application rule that restricts access to a single Client application.

Supervisor

Identities = User with name ‘Root’

Applications =

Endpoints =

An identity mapping rule that specifies specific users that have access to the Role

Administrator

Identities = User with name ‘Root’

Applications =

Endpoints = opc.tcp://127.0.0.1:48000

An identity mapping rule that specifies specific users that have access to the Role when they connect via a specific Endpoint.

 

The examples also make use of the Nodes defined in Table 4. The table specifies the value of the RolePermissions Attribute for each Node.

Table 4 – Example Nodes

Node

Role Permissions

Unit1.Measurement

AuthenticatedUser = Browse

Operator1 = Browse, Read

Unit2.Measurement

AuthenticatedUser = Browse

Operator2 = Browse, Read

SetPoint

AuthenticatedUser = Browse

Operator1 and Operator2 = Browse, Read, Write

Supervisor = Browse, Read

DisableDevice

AuthenticatedUser = Browse

Operator1 and Operator2 = Browse, Read 

Administrator = Browse, Read, Write

 

When a Client creates a Session the Roles assigned to the Session depend on the rules defined for each Role. Table 5 lists the assigned Roles for different Sessions created with different Users, Client applications and Endpoints.

Table 5 – Example Role Assignment

User Provided by Client

Roles Assigned to Session

Anonymous

Anonymous

Sam

AuthenticatedUser

Joe using OperatorStation1 application.

AuthenticatedUser, Operator1

Joe using OperatorStation2 application.

AuthenticatedUser, Operator2

Joe using generic application.

AuthenticatedUser

Root using OperatorStation1 application.

AuthenticatedUser, Supervisor

Root using generic application and 127.0.0.1 endpoint.

AuthenticatedUser, Supervisor, Administrator

Root using generic application and another endpoint.

AuthenticatedUser, Supervisor

 

When a Client application accesses a Node the RolePermissions for the Node are compared to the Roles assigned to the Session. Any Permissions available to at least one Role is granted to the Client. Table 6 provides a number of scenarios and examples and the resulting decision on access.

Table 6 – Examples of Evaluating Access

Use Case

Role Permissions

Anonymous user on localhost browses Unit1.Measurement Node.

Access denied because no rule defined for Anonymous users.

User ‘Sam’ using OperatorStation1 application browses Unit1.Measurement Node.

Allowed because AuthenticatedUser is granted Browse Permission.

User ‘Sam’ using OperatorStation2 application reads Value of Unit1.Measurement Node.

Access denied because AuthenticatedUser is not granted Read Permission.

User ‘Joe’ using OperatorStation1 application reads Value of Unit1.Measurement Node.

Allowed because Operator1 is granted Read Permission.

User ‘Joe’ using OperatorStation2 application reads Value of Unit1.Measurement Node.

Access denied because AuthenticatedUser and Operator2 are not granted Read Permission.

User ‘Joe’ using generic OPC UA application reads Value of Measurement Node.

Access denied because AuthenticatedUser is not granted Read Permission.

User ‘Joe’ using OperatorStation1 application write Value of SetPoint Node.

Allowed because Operator1 is granted Write Permission.

User ‘Root’ using OperatorStation1 application write the Value of SetPoint Node.

Denied because AuthenticatedUser and Supervisor are not granted Write Permission.

User ‘Joe’ using OperatorStation1 application write Value of DisableDevice Node.

Access denied because AuthenticatedUser and Operator1 are not granted Write Permission.

User ‘Root’ using OperatorStation1 application write the Value of DisableDevice Node.

Access denied because AuthenticatedUser and Supervisor are not granted Write Permission.

User ‘Root’ using endpoint 127.0.0.1 to write Value of DisableDevice Node.

Allowed because Administrator is granted Write Permission.

 

5    Standard NodeClasses

5.1    Overview

Clause 5 defines the NodeClasses used to define Nodes in the OPC UA AddressSpace. NodeClasses are derived from a common Base NodeClass. This NodeClass is defined first, followed by those used to organise the AddressSpace and then by the NodeClasses used to represent Objects.

The NodeClasses defined to represent Objects fall into three categories: those used to define instances, those used to define types for those instances and those used to define data types. Subclause 6.3 describes the rules for subtyping and 6.4 the rules for instantiation of the type definitions.

5.2    Base NodeClass

5.2.1   General

The OPC UA Address Space Model defines a Base NodeClass from which all other NodeClasses are derived. The derived NodeClasses represent the various components of the OPC UA Object Model (see 4.2). The Attributes of the Base NodeClass are specified in Table 7. There are no References specified for the Base NodeClass.

Table 7 – Base NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    NodeId

M

NodeId

See 5.2.2

    NodeClass

M

NodeClass

See 5.2.3

    BrowseName

M

QualifiedName

See 5.2.4

    DisplayName

M

LocalizedText

See 5.2.5

    Description

O

LocalizedText

See 5.2.6

    WriteMask

O

AttributeWriteMask

See 5.2.7

    UserWriteMask

O

AttributeWriteMask

See 5.2.8

    RolePermissions

O

RolePermissionType[]

See 5.2.9

    UserRolePermissions

O

RolePermissionType[]

See 5.2.10

    AccessRestrictions

O

AccessRestrictionsType

See 5.2.11

References

 

 

No References specified for this NodeClass

 

5.2.2   NodeId

Nodes are unambiguously identified using a constructed identifier called the NodeId. Some Servers may accept alternative NodeIds in addition to the canonical NodeId represented in this Attribute. A Server shall persist the NodeId of a Node, that is, it shall not generate new NodeIds when rebooting. The structure of the NodeId is defined in 8.2.

5.2.3   NodeClass

The NodeClass Attribute identifies the NodeClass of a Node. Its data type is defined in 8.30.

5.2.4   BrowseName

Nodes have a BrowseName Attribute that is used as a non-localised human-readable name when browsing the AddressSpace to create paths out of BrowseNames. The TranslateBrowsePathsToNodeIds Service defined in OPC 10000-4 can be used to follow a path constructed of BrowseNames.

A BrowseName should never be used to display the name of a Node. The DisplayName should be used instead for this purpose.

Unlike NodeIds, the BrowseName cannot be used to unambiguously identify a Node. Different Nodes may have the same BrowseName.

Subclause 8.3 defines the structure of the BrowseName. It contains a namespace and a string. The namespace is provided to make the BrowseName unique in some cases in the context of a Node (e.g. Properties of a Node) although not unique in the context of the Server. If different organizations define BrowseNames for Properties, the namespace of the BrowseName provided by the organization makes the BrowseName unique, although different organizations may use the same string having a slightly different meaning.

Servers may often choose to use the same namespace for the NodeId and the BrowseName. However, if they want to provide a standard Property, its BrowseName shall have the namespace of the standards body although the namespace of the NodeId reflects something else, for example the local Server.

It is recommended that standard bodies defining standard type definitions use their namespace for the NodeId of the TypeDefinitionNode as well as for the BrowseName of the TypeDefinitionNode.

The string-part of the BrowseName is case sensitive. That is, Clients shall consider them case sensitive. Servers are allowed to handle BrowseNames passed in Service requests as case insensitive. Examples are the TranslateBrowsePathsToNodeIds Service or Event filter.

5.2.5   DisplayName

The DisplayName Attribute contains the localised name of the Node. Clients should use this Attribute if they want to display the name of the Node to the user. They should not use the BrowseName for this purpose. The Server may maintain one or more localised representations for each DisplayName. Clients negotiate the locale to be returned when they open a session with the Server. Refer to OPC 10000-4 for a description of session establishment and locales. Subclause 8.5 defines the structure of the DisplayName. The string part of the DisplayName is restricted to 512 characters.

5.2.6   Description

The optional Description Attribute shall explain the meaning of the Node in a localised text using the same mechanisms for localisation as described for the DisplayName in 5.2.5.

5.2.7   WriteMask

The optional WriteMask Attribute exposes the possibilities of a client to write the Attributes of the Node. The WriteMask Attribute does not take any user access rights into account, that is, although an Attribute is writable this may be restricted to a certain user/user group.

If the OPC UA Server does not have the ability to get the WriteMask information for a specific Attribute from the underlying system, it should state that it is writable. If a write operation is called on the Attribute, the Server should transfer this request and return the corresponding StatusCode if such a request is rejected. StatusCodes are defined in OPC 10000-4.

The AttributeWriteMask DataType is defined in 0.

5.2.8   UserWriteMask

The optional UserWriteMask Attribute exposes the possibilities of a client to write the Attributes of the Node taking user access rights into account. It uses the AttributeWriteMask DataType which is defined in 0.

The UserWriteMask Attribute can only further restrict the WriteMask Attribute, when it is set to not writable in the general case that applies for every user.

Clients cannot assume an Attribute can be written based on the UserWriteMask Attribute.It is possible that the Server may return an access denied error due to some server specific change which was not reflected in the state of this Attribute at the time the Client accessed it.

5.2.9   RolePermissions

The optional RolePermissions Attribute specifies the Permissions that apply to a Node for all Roles which have access to the Node. The value of the Attribute is an array of RolePermissionType Structures (see Table 8).

Table 8 – RolePermissionType

Name

Type

Description

RolePermissionType

Structure

Specifies the Permissions for a Role

    roleId

NodeId

The NodeId of the Role Object.

    permissions

PermissionType

A mask specifying which Permissions are available to the Role.

 

Servers may allow administrators to write to the RolePermissions Attribute.

If not specified, the value of DefaultRolePermissions Property from the NamespaceMetadata Object associated with the Node shall be used instead. If the NamespaceMetadata Object does not define the Property or does not exist, then the Server should not publish any information about how it manages Permissions.

If a Server supports Permissions for a particular Namespace it shall add the DefaultRolePermissions Property to the NamespaceMetadata Object for that Namespace (see Figure 8). If a particular Node in the Namespace needs to override the default values, the Server adds the RolePermissions Attribute to the Node. The DefaultRolePermissions Property and RolePermissions Attribute shall only be readable by administrators. If a Server allows the Permissions to be changed these values shall be writeable. If the Server allows the Permissions to be overridden for a particular Node but does not currently have any Node Permissions configured, then the value of the Attribute shall be an empty array. If the administrator wishes to remove overridden Permissions, an empty array shall be written to this Attribute. Servers shall prevent Permissions from being changed in such a way as to render the Server inoperable.

If a Server publishes information about the Roles for a Namespace assigned to the current Session, it shall add the DefaultUserRolePermissions Property to the NamespaceMetadata Object for that Namespace. The value of this Property shall be a readonly list of Permissions for each Role assigned to the current Session. If a particular Node in the Namespace overrides the default RolePermissions the Server shall also override the DefaultUserRolePermissions by adding the UserRolePermissions Attribute to the Node. If the Server allows the Permissions to be overridden for a particular Node but does not currently have any Node Permissions configured, then the Server shall return the value of the DefaultUserRolePermissions Property for the Node Namespace.

If a Server implements a vendor specific Role Permission model for a Namespace, it shall not add the DefaultRolePermissions or DefaultUserRolePermissions Properties to the Namespace
Metadata
Object.

Figure12_

Figure 8 – Permissions in the Address Space

5.2.10   UserRolePermissions

The optional UserRolePermissions Attribute specifies the Permissions that apply to a Node for all Roles granted to current Session. The value of the Attribute is an array of RolePermissionType Structures (see Table 8).

Clients may determine their effective Permissions by logically ORing the Permissions for each Role in the array.

The value of this Attribute is derived from the rules used by the Server to map Sessions to Roles. This mapping may be vendor specific or it may use the standard Role model defined in 4.8.

This Attribute shall not be writeable.

If not specified, the value of DefaultUserRolePermissions Property from the Namespace Metadata Object associated with the Node is used instead. If the NamespaceMetadata Object does not define the Property or does not exist, then the Server does not publish any information about Roles mapped to the current Session.

5.2.11   AccessRestrictions

The optional AccessRestrictions Attribute specifies the AccessRestrictions that apply to a Node. Its data type is defined in 8.56. If a Server supports AccessRestrictions for a particular Namespace it adds the DefaultAccessRestrictions Property to the NamespaceMetadata Object for that Namespace (see Figure 8). If a particular Node in the Namespace needs to override the default value the Server adds the AccessRestrictions Attribute to the Node.

If a Server implements a vendor specific access restriction model for a Namespace, it does not add the DefaultAccessRestrictions Property to the NamespaceMetadata Object.

5.3    ReferenceType NodeClass

5.3.1   General

References are defined as instances of ReferenceType Nodes. ReferenceType Nodes are visible in the AddressSpace and are defined using the ReferenceType NodeClass as specified in Table 9. In contrast, a Reference is an inherent part of a Node and no NodeClass is used to represent References.

This standard defines a set of ReferenceTypes provided as an inherent part of the OPC UA Address Space Model. These ReferenceTypes are defined in Clause 7 and their representation in the AddressSpace is defined in OPC 10000-5. Servers may also define ReferenceTypes. In addition, OPC 10000-4 defines NodeManagement Services that allow Clients to add ReferenceTypes to the AddressSpace.

Table 9 – ReferenceType NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

   Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

   IsAbstract

M

Boolean

A boolean Attribute with the following values:

   TRUE       it is an abstract ReferenceType, i.e. no Reference of this type shall exist, only of its subtypes.

   FALSE      it is not an abstract ReferenceType, i.e. References of this type can exist.

   Symmetric

M

Boolean

A boolean Attribute with the following values:

   TRUE       the meaning of the ReferenceType is the same as seen from both the SourceNode and the TargetNode.

   FALSE     the meaning of the ReferenceType as seen from the TargetNode is the inverse of that as seen from the SourceNode.

   InverseName

O

LocalizedText

The inverse name of the Reference, which is the meaning of the ReferenceType as seen from the TargetNode.

 

 

 

 

References

 

 

 

   HasProperty

0..*

 

Used to identify the Properties (see 5.3.3.2).

   HasSubtype

0..*

 

Used to identify subtypes (see 5.3.3.3).

 

 

 

 

Standard Properties

 

 

 

   NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

 

5.3.2   Attributes

The ReferenceType NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2. The inherited BrowseName Attribute is used to specify the meaning of the ReferenceType as seen from the SourceNode. For example, the ReferenceType with the BrowseName “Contains” is used in References that specify that the SourceNode contains the TargetNode. The inherited DisplayName Attribute contains a translation of the BrowseName.

The BrowseName of a ReferenceType shall be unique in a Server. It is not allowed that two different ReferenceTypes have the same BrowseName.

The IsAbstract Attribute indicates if the ReferenceType is abstract. Abstract ReferenceTypes cannot be instantiated and are used only for organizational reasons, for example to specify some general semantics or constraints that its subtypes inherit.

The Symmetric Attribute is used to indicate whether or not the meaning of the ReferenceType is the same for both the SourceNode and TargetNode.

If a ReferenceType is symmetric, the InverseName Attribute shall be omitted. Examples of symmetric ReferenceTypes are “Connects To” and “Communicates With”. Both imply the same semantic coming from the SourceNode or the TargetNode. Therefore both directions are considered to be forward References.

If the ReferenceType is non-symmetric and not abstract, the InverseName Attribute shall be set. The InverseName Attribute specifies the meaning of the ReferenceType as seen from the TargetNode. Examples of non-symmetric ReferenceTypes include “Contains” and “Contained In”, and “Receives From” and “Sends To”.

References that use the InverseName, such as “Contained In” References, are referred to as inverse References.

Figure 9 provides examples of symmetric and non-symmetric References and the use of the BrowseName and the InverseName.

Figure13_

Figure 9 – Symmetric and Non-Symmetric References

It might not always be possible for Servers to instantiate both forward and inverse References for non-symmetric ReferenceTypes as shown in Figure 9. When they do, the References are referred to as bidirectional. Although not required, it is recommended that all hierarchical References be instantiated as bidirectional to ensure browse connectivity. A bidirectional Reference is modelled as two separate References.

As an example of a unidirectional Reference, it is often the case that a signal sink knows its signal source, but this signal source does not know its signal sink. The signal sink would have a “Sourced By” Reference to the signal source, without the signal source having the corresponding “Sourced To” inverse References to its signal sinks.

The DisplayName and the InverseName are the only standardised places to indicate the semantic of a ReferenceType. There may be more complex semantics associated with a ReferenceType than can be expressed in those Attributes (e.g. the semantic of HasSubtype). This standard does not specify how this semantic should be exposed. However, the Description Attribute can be used for this purpose. This standard provides a semantic for the ReferenceTypes specified in Clause 7.

A ReferenceType can have constraints restricting its use. For example, it can specify that starting from Node A and only following References of this ReferenceType or one of its subtypes, it shall never be able to return to A, that is, a “No Loop” constraint.

This standard does not specify how those constraints could or should be made available in the AddressSpace. Nevertheless, for the standard ReferenceTypes, some constraints are specified in Clause 7. This standard does not restrict the kind of constraints valid for a ReferenceType. It can, for example, also affect an ObjectType. The restriction that a ReferenceType can only be used by relating Nodes of some NodeClasses with a defined cardinality is a special constraint of a ReferenceType.

5.3.3   References

5.3.3.1   General

HasSubtype References and HasProperty References are the only ReferenceTypes that may be used with ReferenceType Nodes as SourceNode. ReferenceType Nodes shall not be the SourceNode of other types of References.

5.3.3.2   HasProperty References

HasProperty References are used to identify the Properties of a ReferenceType and shall only refer to Nodes of the Variable NodeClass.

The Property NodeVersion is used to indicate the version of the ReferenceType.

There are no additional Properties defined for ReferenceTypes in this standard. Additional parts this series of standards may define additional Properties for ReferenceTypes.

5.3.3.3   HasSubtype References

HasSubtype References are used to define subtypes of ReferenceTypes. It is not required to provide the HasSubtype Reference for the supertype, but it is required that the subtype provides the inverse Reference to its supertype. The following rules for subtyping apply.

a)   The semantic of a ReferenceType (e.g. “spans a hierarchy”) is inherited to its subtypes and can be refined there (e.g. “spans a special hierarchy”). The DisplayName, and also the InverseName for non-symmetric ReferenceTypes, reflect the specialization.

b)   If a ReferenceType specifies some constraints (e.g. “allow no loops”) this is inherited and can only be refined (e.g. inheriting “no loops” could be refined as “shall be a tree – only one parent”) but not lowered (e.g. “allow loops”).

c)    The constraints concerning which NodeClasses can be referenced are also inherited and can only be further restricted. That is, if a ReferenceType “A” is not allowed to relate an Object with an ObjectType, this is also true for its subtypes.

d)   A ReferenceType shall have exactly one supertype, except for the References ReferenceType defined in 7.2 as the root type of the ReferenceType hierarchy. The ReferenceType hierarchy does not support multiple inheritances.

5.4    View NodeClass

Underlying systems are often large and Clients often have an interest in only a specific subset of the data. They do not need, or want, to be burdened with viewing Nodes in the AddressSpace for which they have no interest.

To address this problem, this standard defines the concept of a View. Each View defines a subset of the Nodes in the AddressSpace. The entire AddressSpace is the default View. Each Node in a View may contain only a subset of its References, as defined by the creator of the View. The View Node acts as the root for the Nodes in the View. Views are defined using the View NodeClass, which is specified in Table 10.

All Nodes contained in a View shall be accessible starting from the View Node when browsing in the context of the View. It is not expected that all containing Nodes can be browsed directly from the View Node but rather browsed from other Nodes contained in the View.

A View Node may not only be used as additional entry point into the AddressSpace but as a construct to organize the AddressSpace and thus as the only entry point into a subset of the AddressSpace. Therefore Clients shall not ignore View Nodes when exposing the AddressSpace. Simple Clients that do not deal with Views for filtering purposes can, for example, handle a View Node like an Object of type FolderType (see 5.5.3).

Table 10 – View NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

    ContainsNoLoops

M

Boolean

If set to “true” this Attribute indicates that by following the References in the context of the View there are no loops, i.e. starting from a Node “A” contained in the View and following the forward References in the context of the View Node “A” will not be reached again. It does not specify that there is only one path starting from the View Node to reach a Node contained in the View.

If set to “false” this Attribute indicates that following References in the context of the View may lead to loops.

    EventNotifier

M

Byte

The EventNotifier Attribute is used to indicate if the Node can be used to subscribe to Events or to read / write historic Events.

The EventNotifier is an 8-bit unsigned integer with the structure defined in the following table.

 

Field

Bit

Description

SubscribeTo Events

0

Indicates if it can be used to subscribe to Events
(0 means cannot be used to subscribe to Events, 1 means can be used to subscribe to Events)

Reserved

1

Reserved for future use. Shall always be zero.

HistoryRead

2

Indicates if the history of the Events is readable
(0 means not readable, 1 means readable)

HistoryWrite

3

Indicates if the history of the Events is writable
(0 means not writable, 1 means writable)

Reserved

4:7

Reserved for future use. Shall always be zero

 

The second two bits also indicate if the history of the Events is available via the OPC UA Server.

 

 

 

 

References

 

 

 

    HierarchicalReferences

0..*

 

Top level Nodes in a View are referenced by hierarchical References (see 7.3).

    HasProperty

0..*

 

HasProperty References identify the Properties of the View.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

    ViewVersion

O

UInt32

The version number for the View. When Nodes are added to or removed from a View, the value of the ViewVersion Property is updated. Clients may detect changes to the composition of a View using this Property. The value of the ViewVersion shall always be greater than 0.

 

The View NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2. It also defines two additional Attributes.

The mandatory ContainsNoLoops Attribute is set to false if the Server is not able to identify if the View contains loops or not.

The mandatory EventNotifier Attribute identifies if the View can be used to subscribe to Events that either occur in the content of the View or as ModelChangeEvents (see 9.32) of the content of the View or to read / write the history of the Events. A View that supports Events shall provide all Events that occur in any Object used as EventNotifier that is part of the content of the View. In addition, it shall provide all ModelChangeEvents that occur in the context of the View.

To avoid recursion, i.e. getting all Events of the Server, the Server Object defined in OPC 10000-5 shall never be part of any View since it provides all Events of the Server.

Views are defined by the Server. The browsing and querying Services defined in OPC 10000-4 expect the NodeId of a View Node to provide these Services in the context of the View.

HasProperty References are used to identify the Properties of a View. The Property NodeVersion is used to indicate the version of the View Node. The ViewVersion Property indicates the version of the content of the View. In contrast to the NodeVersion, the ViewVersion Property is updated even if Nodes not directly referenced by the View Node are added to or deleted from the View. This Property is optional because it might not be possible for Servers to detect changes in the View contents. Servers may also generate a ModelChangeEvent, described in 9.32, if Nodes are added to or deleted from the View. There are no additional Properties defined for Views in this document. Additional parts of this series of standards may define additional Properties for Views.

Views can be the SourceNode of any hierarchical Reference. They shall not be the SourceNode of any non-hierarchical Reference.

5.5    Objects

5.5.1   Object NodeClass

Objects are used to represent systems, system components, real-world objects and software objects. Objects are defined using the Object NodeClass, specified in Table 11.

Table 11 – Object NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

    EventNotifier

M

EventNotifierType

The EventNotifier Attribute is used to indicate if the Node can be used to subscribe to Events or the read / write historic Events.

The EventNotifierType is defined in  0.

 

 

 

 

References

 

 

 

    HasComponent

0..*

 

HasComponent References identify the DataVariables, the Methods and Objects contained in the Object.

    HasProperty

0..*

 

HasProperty References identify the Properties of the Object.

    HasModellingRule

0..1

 

Objects can point to at most one ModellingRule Object using a HasModellingRule Reference (see 6.4.4 for details on ModellingRules).

    HasTypeDefinition

1

 

The HasTypeDefinition Reference points to the type definition of the Object. Each Object shall have exactly one type definition and therefore be the SourceNode of exactly one HasTypeDefinition Reference pointing to an ObjectType. See 4.5 for a description of type definitions.

    HasEventSource

0..*

 

The HasEventSource Reference points to event sources of the Object. References of this type can only be used for Objects having their “SubscribeToEvents” bit set in the EventNotifier Attribute. See 7.17 for details.

    HasNotifier

0..*

 

The HasNotifier Reference points to notifiers of the Object. References of this type can only be used for Objects having their “SubscribeToEvents” bit set in the EventNotifier Attribute. See 7.18 for details.

    Organizes

0..*

 

This Reference should be used only for Objects of the ObjectType FolderType (see 5.5.3).

    <other References>

0..*

 

Objects may contain other References.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

    Icon

O

Image

The Icon Property provides an image that can be used by Clients when displaying the Node. It is expected that the Icon Property contains a relatively small image.

    NamingRule

O

NamingRuleType

The NamingRule Property defines the NamingRule of a ModellingRule (see 6.4.4.2.1 for details). This Property shall only be used for Objects of the type ModellingRuleType defined in 6.4.4.

 

The Object NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2.

The mandatory EventNotifier Attribute identifies whether the Object can be used to subscribe to Events or to read and write the history of the Events.

The Object NodeClass uses the HasComponent Reference to define the DataVariables, Objects and Methods of an Object.

It uses the HasProperty Reference to define the Properties of an Object. The Property NodeVersion is used to indicate the version of the Object. The Property Icon provides an icon of the Object. The Property NamingRule defines the NamingRule of a ModellingRule and shall only be applied to Objects of type ModellingRuleType. There are no additional Properties defined for Objects in this document. Additional parts of this series of standards may define additional Properties for Objects.

To specify its ModellingRule, an Object can use at most one HasModellingRule Reference pointing to a ModellingRule Object. ModellingRules are defined in 6.4.4.

HasNotifier and HasEventSource References are used to provide information about eventing and can only be applied to Objects used as event notifiers. Details are defined in 7.16 and 7.18.

The HasTypeDefinition Reference points to the ObjectType used as type definition of the Object.

Objects may use any additional References to define relationships to other Nodes. No restrictions are placed on the types of References used or on the NodeClasses of the Nodes that may be referenced. However, restrictions may be defined by the ReferenceType excluding its use for Objects. Standard ReferenceTypes are described in Clause 7.

If the Object is used as an InstanceDeclaration (see 4.5) then all Nodes referenced with forward hierarchical References direction shall have unique BrowseNames in the context of this Object.

If the Object is created based on an InstanceDeclaration then it shall have the same BrowseName as its InstanceDeclaration.

5.5.2   ObjectType NodeClass

ObjectTypes provide definitions for Objects. ObjectTypes are defined using the ObjectType NodeClass, which is specified in Table 12.

Table 12 – ObjectType NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

    IsAbstract

M

Boolean

A boolean Attribute with the following values:

    TRUE          it is an abstract ObjectType, i.e. no Objects of this type shall exist, only Objects of its subtypes.

    FALSE         it is not an abstract ObjectType, i.e. Objects of this type can exist.

 

 

 

 

References

 

 

 

    HasComponent

0..*

 

HasComponent References identify the DataVariables, the Methods, and Objects contained in the ObjectType.

If and how the referenced Nodes are instantiated when an Object of this type is instantiated, is specified in 6.4.

    HasProperty

0..*

 

HasProperty References identify the Properties of the ObjectType. If and how the Properties are instantiated when an Object of this type is instantiated, is specified in 6.4.

    HasSubtype

0..*

 

HasSubtype References identify ObjectTypes that are subtypes of this type. The inverse SubtypeOf Reference identifies the parent type of this type.

    GeneratesEvent

0..*

 

GeneratesEvent References identify the type of Events instances of this type may generate.

    <other References>

0..*

 

ObjectTypes may contain other References that can be instantiated by Objects defined by this ObjectType.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

    Icon

O

Image

The Icon Property provides an image that can be used by Clients when displaying the Node. It is expected that the Icon Property contains a relatively small image.

 

The ObjectType NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2. The additional IsAbstract Attribute indicates if the ObjectType is abstract or not.

The ObjectType NodeClass uses the HasComponent References to define the DataVariables, Objects, and Methods for it.

The HasProperty Reference is used to identify the Properties. The Property NodeVersion is used to indicate the version of the ObjectType. The Property Icon provides an icon of the ObjectType. There are no additional Properties defined for ObjectTypes in this document. Additional parts of this series of standards may define additional Properties for ObjectTypes.

HasSubtype References are used to subtype ObjectTypes. ObjectType subtypes inherit the general semantics from the parent type. The general rules for subtyping apply as defined in Clause 6. It is not required to provide the HasSubtype Reference for the supertype, but it is required that the subtype provides the inverse Reference to its supertype.

GeneratesEvent References identify the type of Events that instances of the ObjectType may generate. These Objects may be the source of an Event of the specified type or one of its subtypes. Servers should make GeneratesEvent References bidirectional References. However, it is allowed to be unidirectional when the Server is not able to expose the inverse direction pointing from the EventType to each ObjectType supporting the EventType. Note that the EventNotifier Attribute of an Object and the GeneratesEvent References of its ObjectType are completely unrelated. Objects that can generate Events might not be used as Objects to which Clients subscribe to get the corresponding Event notifications.

GeneratesEvent References are optional, i.e. Objects may generate Events of an EventType that is not exposed by its ObjectType.

ObjectTypes may use any additional References to define relationships to other Nodes. No restrictions are placed on the types of References used or on the NodeClasses of the Nodes that may be referenced. However, restrictions may be defined by the ReferenceType excluding its use for ObjectTypes. Standard ReferenceTypes are described in Clause 7.

All Nodes referenced with forward hierarchical References shall have unique BrowseNames in the context of an ObjectType (see 4.5).

5.5.3   Standard ObjectType FolderType

The ObjectType FolderType is formally defined in OPC 10000-5. Its purpose is to provide Objects that have no other semantic than organizing of the AddressSpace. A special ReferenceType is introduced for those Folder Objects, the Organizes ReferenceType. The SourceNode of such a Reference should always be a View or an Object of the ObjectType FolderType; the TargetNode can be of any NodeClass. Organizes References can be used in any combination with HasChild References (HasComponent, HasProperty, etc.; see 7.5) and do not prevent loops. Thus, they can be used to span multiple hierarchies.

5.5.4   Client-side creation of Objects of an ObjectType

Objects are always based on an ObjectType, i.e. they have a HasTypeDefinition Reference pointing to its ObjectType.

Clients can create Objects using the AddNodes Service defined in OPC 10000-4. The Service requires specifying the TypeDefinitionNode of the Object. An Object created by the AddNodes Service contains all components defined by its ObjectType dependent on the ModellingRules specified for the components. However, the Server may add additional components and References to the Object and its components that are not defined by the ObjectType. This behaviour is Server dependent. The ObjectType only specifies the minimum set of components that shall exist for each Object of an ObjectType.

In addition to the AddNodes Service ObjectTypes may have a special Method with the BrowseNameCreate”. This Method is used to create an Object of this ObjectType. This Method may be useful for the creation of Objects where the semantic of the creation should differ from the default behaviour expected in the context of the AddNodes Service. For example, the values should directly differ from the default values or additional Objects should be added, etc. The input and output arguments of this Method depend on the ObjectType; the only commonality is the BrowseName identifying that this Method will create an Object based on the ObjectType. Servers should not provide a Method on an ObjectType with the BrowseNameCreate” for any other purpose than creating Objects of the ObjectType.

5.6    Variables

5.6.1   General

Two types of Variables are defined, Properties and DataVariables. Although they differ in the way they are used as described in 4.4 and have different constraints described in the remainder of 5.6 they use the same NodeClass described in 5.6.2. The constraints of Properties based on this NodeClass are defined in 5.6.3, the constraints of DataVariables in 5.6.4.

5.6.2   Variable NodeClass

Variables are used to represent values which may be simple or complex. Variables are defined by VariableTypes, as specified in 5.6.5.

Variables are always defined as Properties or DataVariables of other Nodes in the AddressSpace. They are never defined by themselves. A Variable is always part of at least one other Node, but may be related to any number of other Nodes. Variables are defined using the Variable NodeClass, specified in Table 13.

Table 13 – Variable NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

    Value

M

Defined by the DataType Attribute

The most recent value of the Variable that the Server has. Its data type is defined by the DataType Attribute. It is the only Attribute that does not have a data type associated with it. This allows all Variables to have a value defined by the same Value Attribute.

    DataType

M

NodeId

NodeId of the DataType definition for the Value Attribute. Standard DataTypes are defined in Clause 8.

    ValueRank

M

Int32

This Attribute indicates whether the Value Attribute of the Variable is an array and how many dimensions the array has.

It may have the following values:

n > 1: the Value is an array with the specified number of dimensions.

OneDimension (1): The value is an array with one dimension.

OneOrMoreDimensions (0): The value is an array with one or more dimensions.

Scalar (1): The value is not an array.

Any (2): The value can be a scalar or an array with any number of dimensions.

ScalarOrOneDimension (3): The value can be a scalar or a one dimensional array.

All DataTypes are considered to be scalar, even if they have array-like semantics like ByteString and String.

    ArrayDimensions

O

UInt32[]

This Attribute specifies the maximum supported length of each dimension. If the maximum is unknown the value shall be 0.

The number of elements shall be equal to the value of the ValueRank Attribute. This Attribute shall be null if ValueRank 0.

 

For example, if a Variable is defined by the following C array:

    Int32 myArray[346];

then this Variable’s DataType would point to an Int32 and the Variable’s ValueRank has the value 1 and the ArrayDimensions is an array with one entry having the value 346.

 

The maximum number of elements of an array transferred on the wire is 2147483647 (max Int32).

    AccessLevel

M

AccessLevelType

The AccessLevel Attribute is used to indicate how the Value of a Variable can be accessed (read/write) and if it contains current and/or historic data. The AccessLevel does not take any user access rights into account, i.e. although the Variable is writable this may be restricted to a certain user / user group.

The AccessLevelType is defined in 8.57.

 

    UserAccessLevel

M

AccessLevelType

The UserAccessLevel Attribute is used to indicate how the Value of a Variable can be accessed (read/write) and if it contains current or historic data taking user access rights into account.

The AccessLevelType is defined in 8.57.

 

    MinimumSamplingInterval

O

Duration

The MinimumSamplingInterval Attribute indicates how “current” the Value of the Variable will be kept. It specifies (in milliseconds) how fast the Server can reasonably sample the value for changes (see OPC 10000-4 for a detailed description of sampling interval).

A MinimumSamplingInterval of 0 indicates that the Server is to monitor the item continuously. A MinimumSamplingInterval of -1 means indeterminate.

    Historizing

M

Boolean

The Historizing Attribute indicates whether the Server is actively collecting data for the history of the Variable. This differs from the AccessLevel Attribute which identifies if the Variable has any historical data. A value of TRUE indicates that the Server is actively collecting data. A value of FALSE indicates the Server is not actively collecting data. Default value is FALSE.

    AccessLevelEx

O

AccessLevelExType

 

The AccessLevelEx Attribute is used to indicate how the Value of a Variable can be accessed (read/write), if it contains current and/or historic data and its atomicity. The AccessLevelEx does not take any user access rights into account, i.e. although the Variable is writable this may be restricted to a certain user / user group. The AccessLevelEx is an extended version of the AccessLevel attribute and as such contains the 8 bits of the AccessLevel attribute as the first 8 bits.

The AccessLevelEx is a 32-bit unsigned integer with the structure defined in the 8.58.

 

If this Attribute is not provided the information provided by these additional Fields is unknown.

 

 

 

 

References

 

 

 

    HasModellingRule

0..1

 

Variables can point to at most one ModellingRule Object using a HasModellingRule Reference (see 6.4.4 for details on ModellingRules).

    HasProperty

0..*

 

HasProperty References are used to identify the Properties of a DataVariable.

Properties are not allowed to be the SourceNode of HasProperty References.

    HasComponent

0..*

 

HasComponent References are used by complex DataVariables to identify their composed DataVariables.

Properties are not allowed to use this Reference.

    HasTypeDefinition

1

 

The HasTypeDefinition Reference points to the type definition of the Variable. Each Variable shall have exactly one type definition and therefore be the SourceNode of exactly one HasTypeDefinition Reference pointing to a VariableType. See 4.5 for a description of type definitions.

    <other References>

0..*

 

Data Variables may be the SourceNode of any other References.

Properties may only be the SourceNode of any non-hierarchical Reference.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a DataVariable. It does not apply to Properties.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes except for the DataType Attribute do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

Although the relationship of a Variable to its DataType is not modelled using References, changes to the DataType Attribute of a Variable lead to an update of the NodeVersion Property.

    LocalTime

O

TimeZone
DataType

The LocalTime Property is only used for DataVariables. It does not apply to Properties.

This Property is a structure containing the Offset and the DaylightSavingInOffset flag. The Offset specifies the time difference (in minutes) between the SourceTimestamp (UTC) associated with the value and the time at the location in which the value was obtained. The SourceTimestamp is defined in OPC 10000-4.

If DaylightSavingInOffset is TRUE, then Standard/Daylight savings time (DST) at the originating location is in effect and Offset includes the DST correction. If FALSE then the Offset does not include DST correction and DST may or may not have been in effect.

    AllowNulls

O

Boolean

The AllowNulls Property is only used for DataVariables. It does not apply to Properties.

This Property specifies if a null value is allowed for the Value Attribute of the DataVariable. If it is set to true, the Server may return null values and accept writing of null values. If it is set to false, the Server shall never return a null value and shall reject any request writing a null value.

If this Property is not provided, it is Server-specific if null values are allowed or not.

    ValueAsText

O

Localized
Text

It is used for DataVariables with a finite set of LocalizedTexts associated with its value. For example any DataVariables having an Enumeration DataType.

This optional Property provides the localized text representation of the value. It can be used by Clients only interested in displaying the text to subscribe to the Property instead of the value attribute.

    MaxStringLength

O

UInt32

Only used for DataVariables having a String DataType.

This optional Property indicates the maximum number of bytes supported by the DataVariable.

    MaxCharacters

O

UInt32

Only used for DataVariables having a String DataType.

This optional Property indicates the maximum number of Unicode characters supported by the DataVariable.

    MaxByteStringLength

O

UInt32

Only used for DataVariables having a ByteString DataType.

This optional Property indicates the maximum number of bytes supported by the DataVariable.

    MaxArrayLength

O

UInt32

Only used for DataVariables having its ValueRank Attribute not set to scalar.

This optional Property indicates the maximum length of an array supported by the DataVariable. In a multidimensional array it indicates the overall length. For example, a three-dimensional array of 2 x 3 x 10 has the array length of 60.

NOTE In order to expose the length of an array of bytes do not use the DataType ByteString but an array of the DataType Byte. In that case the MaxArrayLength applies.

    EngineeringUnits

O

EU
Information

Only used for DataVariables having a Number DataType.

This optional Property indicates the engineering units for the value of the DataVariable (e.g. hertz or seconds). Details about the Property and what engineering units should be used are defined in
OPC 10000-8. The DataType EUInformation is also defined in OPC 10000-8.

 

The Variable NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2.

The Variable NodeClass also defines a set of Attributes that describe the Variable’s Runtime value. The Value Attribute represents the Variable value. The DataType, ValueRank and ArrayDimensions Attributes provide the capability to describe simple and complex values.

The AccessLevel Attribute indicates the accessibility of the Value of a Variable not taking user access rights into account. If the OPC UA Server does not have the ability to get the AccessLevel information from the underlying system then it should state that it is readable and writable. If a read or write operation is called on the Variable then the Server should transfer this request and return the corresponding StatusCode even if such a request is rejected. StatusCodes are defined in OPC 10000-4.

The SemanticChange flag of the AccessLevel Attribute is used for Properties that may change and define semantic aspects of the parent Node. For example, the EngineeringUnit Property describes the semantic of a DataVariable, whereas the Icon Property does not. In this example, if the EngineeringUnit Property may change while the Server is running, the SemanticChange flag shall be set for it.

Servers that support Event subscriptions shall generate a SemanticChangeEvent whenever a Property with SemanticChange flag set changes.

If a Variable having a Property with SemanticChange flag set is used in a Subscription and the Property value changes, then the SemanticsChanged bit of the StatusCode shall be set as defined in OPC 10000-4. Clients subscribing to a Variable should look at the StatusCode to identify if the semantic has changed and retrieve the relevant Properties before processing the value returned from the Subscription.

The UserAccessLevel Attribute indicates the accessibility of the Value of a Variable taking user access rights into account. If the OPC UA Server does not have the ability to get any user access rights related information from the underlying system then it should use the same bit mask as used in the AccessLevel Attribute. The UserAccessLevel Attribute can restrict the accessibility indicated by the AccessLevel Attribute, but not exceed it. Clients should not assume access rights based on the UserAccessLevel Attribute. For example it is possible that the Server returns an error due to some server specific change which was not reflected in the state of this Attribute at the time the Client accessed the Variable.

The MinimumSamplingInterval Attribute specifies how fast the Server can reasonably sample the value for changes. The accuracy of this value (the ability of the Server to attain “best case” performance) can be greatly affected by system load and other factors.

The Historizing Attribute indicates whether the Server is actively collecting data for the history of the Variable. See OPC 10000-11 for details on historizing Variables.

Clients may read or write Variable values, or monitor them for value changes, as specified in OPC 10000-4. OPC 10000-8 defines additional rules when using the Services for automation data.

To specify its ModellingRule, a Variable can use at most one HasModellingRule Reference pointing to a ModellingRule Object. ModellingRules are defined in 6.4.4.

If the Variable is created based on an InstanceDeclaration (see 4.5) it shall have the same BrowseName as its InstanceDeclaration.

The other References are described separately for Properties and DataVariables in the remainder of 5.6

5.6.3   Properties

Properties are used to define the characteristics of Nodes. Properties are defined using the Variable NodeClass, specified in Table 13. However, they restrict their use.

Properties are the leaf of any hierarchy; therefore they shall not be the SourceNode of any hierarchical References. This includes the HasComponent or HasProperty Reference, that is, Properties do not contain Properties and cannot expose their complex structure. However, they may be the SourceNode of any non-hierarchical References.

The HasTypeDefinition Reference points to the VariableType of the Property. Since Properties are uniquely identified by their BrowseName, all Properties shall point to the PropertyType defined in OPC 10000-5.

Properties shall always be defined in the context of another Node and shall be the TargetNode of at least one HasProperty Reference. To distinguish them from DataVariables, they shall not be the TargetNode of any HasComponent Reference. Thus, a HasProperty Reference pointing to a Variable Node defines this Node as a Property.

The BrowseName of a Property is always unique in the context of a Node. It is not permitted for a Node to refer to two Variables using HasProperty References having the same BrowseName.

5.6.4   DataVariable

DataVariables represent the content of an Object. DataVariables are defined using the Variable NodeClass, specified in Table 13.

DataVariables identify their Properties using HasProperty References. Complex DataVariables use HasComponent References to expose their component DataVariables.

The Property NodeVersion indicates the version of the DataVariable.

The Property LocalTime indicates the difference between the SourceTimestamp of the value and the standard time at the location in which the value was obtained.

The Property AllowNulls indicates if null values are allowed for the Value Attribute.

The Property ValueAsText provides a localized text representation for enumeration values.

The Property MaxStringLength indicates the maximum number of bytes of a String value. If a Server does not impose a maximum number of bytes or is not able to determine the maximum number of bytes this Property shall not be provided. If this Property is provided then the MaxCharacters Property shall not be provided.

The Property MaxCharacters indicates the maximum number of Unicode characters of a string value. If a Server does not impose a maximum number of Unicode characters or is not able to determine the maximum number of Unicode characters this Property shall not be provided. If this Property is provided then the MaxStringLength Property shall not be provided.

The Property MaxByteStringLength indicates the maximum number of bytes of a ByteString value. If a Server does not impose a maximum number of bytes or is not able to determine the maximum number of bytes this Property shall not be provided.

The Property MaxArrayLength indicates the maximum allowed array length of the value.

The Property EngineeringUnits indicates the engineering units of the value. There are no additional Properties defined for DataVariables in this part of this document. Additional parts of this series of standards may define additional Properties for DataVariables. OPC 10000-8 defines a set of Properties that can be used for DataVariables.

DataVariables may use additional References to define relationships to other Nodes. No restrictions are placed on the types of References used or on the NodeClasses of the Nodes that may be referenced. However, restrictions may be defined by the ReferenceType excluding its use for DataVariables. Standard ReferenceTypes are described in Clause 7.

A DataVariable is intended to be defined in the context of an Object. However, complex DataVariables may expose other DataVariables, and ObjectTypes and complex VariableTypes may also contain DataVariables. Therefore each DataVariable shall be the TargetNode of at least one HasComponent Reference coming from an Object, an ObjectType, a DataVariable or a VariableType. DataVariables shall not be the TargetNode of any HasProperty References. Therefore, a HasComponent Reference pointing to a Variable Node identifies it as a DataVariable.

The HasTypeDefinition Reference points to the VariableType used as type definition of the DataVariable.

If the DataVariable is used as InstanceDeclaration (see 4.5) all Nodes referenced with forward hierarchical References shall have unique BrowseNames in the context of this DataVariable.

5.6.5   VariableType NodeClass

VariableTypes are used to provide type definitions for Variables. VariableTypes are defined using the VariableType NodeClass, as specified in Table 14.

Table 14 – VariableType NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2

    Value

O

Defined by the DataType attribute

The default Value for instances of this type.

    DataType

M

NodeId

NodeId of the data type definition for instances of this type.

    ValueRank

M

Int32

This Attribute indicates whether the Value Attribute of the VariableType is an array and how many dimensions the array has.

It may have the following values:

> 1: the Value is an array with the specified number of dimensions.

OneDimension (1): The value is an array with one dimension.

OneOrMoreDimensions (0): The value is an array with one or more dimensions.

Scalar (1): The value is not an array.

Any (2): The value can be a scalar or an array with any number of dimensions.

ScalarOrOneDimension (3): The value can be a scalar or a one dimensional array.

NOTE All DataTypes are considered to be scalar, even if they have array-like semantics like ByteString and String.

    ArrayDimensions

O

UInt32[]

This Attribute specifies the length of each dimension for an array value. The Attribute specifies the maximum supported length of each dimension. If the maximum is unknown the value is 0.

The number of elements shall be equal to the value of the ValueRank Attribute. This Attribute shall be null if ValueRank ≤ 0.

For example, if a VariableType is defined by the following C array:

    Int32 myArray[346];

then this VariableType’s DataType would point to an Int32, the VariableType’s ValueRank has the value 1 and the ArrayDimensions is an array with one entry having the value 346.

    IsAbstract

M

Boolean

A boolean Attribute with the following values:

    TRUE          it is an abstract VariableType, i.e. no Variable of this type shall exist, only of its subtypes.

    FALSE         it is not an abstract VariableType, i.e. Variables of this type can exist.

 

 

 

 

References

 

 

 

    HasProperty

0..*

 

HasProperty References are used to identify the Properties of the VariableType. The referenced Nodes may be instantiated by the instances of this type, depending on the ModellingRules defined in 6.4.4.

    HasComponent

0..*

 

HasComponent References are used for complex VariableTypes to identify their containing DataVariables. Complex VariableTypes can only be used for DataVariables. The referenced Nodes may be instantiated by the instances of this type, depending on the ModellingRules defined in 6.4.4.

    HasSubtype

0..*

 

HasSubtype References identify VariableTypes that are subtypes of this type. The inverse subtype of Reference identifies the parent type of this type.

    GeneratesEvent

0..*

 

GeneratesEvent References identify the type of Events instances of this type may generate.

    <other References>

0..*

 

VariableTypes may contain other References that can be instantiated by Variables defined by this VariableType. ModellingRules are defined in 6.4.4.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes except for the DataType Attribute do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

Although the relationship of a VariableType to its DataType is not modelled using References, changes to the DataType Attribute of a VariableType lead to an update of the NodeVersion Property.

The VariableType NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2. The VariableType NodeClass also defines a set of Attributes that describe the default or initial value of its instance Variables. The Value Attribute represents the default value. The DataType, ValueRank and ArrayDimensions Attributes provide the capability to describe simple and complex values. The IsAbstract Attribute defines if the type can be directly instantiated.

The VariableType NodeClass uses HasProperty References to define the Properties and HasComponent References to define DataVariables. Whether they are instantiated depends on the ModellingRules defined in 6.4.4.

The Property NodeVersion indicates the version of the VariableType. There are no additional Properties defined for VariableTypes in this document. Additional parts of this series of standards may define additional Properties for VariableTypes. OPC 10000-8 defines a set of Properties that can be used for VariableTypes.

HasSubtype References are used to subtype VariableTypes. VariableType subtypes inherit the general semantics from the parent type. The general rules for subtyping are defined in Clause 6. It is not required to provide the HasSubtype Reference for the supertype, but it is required that the subtype provides the inverse Reference to its supertype.

GeneratesEvent References identify that Variables of the VariableType may be the source of an Event of the specified EventType or one of its subtypes. Servers should make GeneratesEvent References bidirectional References. However, it is allowed to be unidirectional when the Server is not able to expose the inverse direction pointing from the EventType to each VariableType supporting the EventType.

GeneratesEvent References are optional, i.e. Variables may generate Events of an EventType that is not exposed by its VariableType.

VariableTypes may use any additional References to define relationships to other Nodes. No restrictions are placed on the types of References used or on the NodeClasses of the Nodes that may be referenced. However, restrictions may be defined by the ReferenceType excluding its use for VariableTypes. Standard ReferenceTypes are described in Clause 7.

All Nodes referenced with forward hierarchical References shall have unique BrowseNames in the context of the VariableType (see 4.5).

5.6.6   Client-side creation of Variables of an VariableType

Variables are always based on a VariableType, i.e. they have a HasTypeDefinition Reference pointing to its VariableType.

Clients can create Variables using the AddNodes Service defined in OPC 10000-4. The Service requires specifying the TypeDefinitionNode of the Variable. A Variable created by the AddNodes Service contains all components defined by its VariableType dependent on the ModellingRules specified for the components. However, the Server may add additional components and References to the Variable and its components that are not defined by the VariableType. This behaviour is Server dependent. The VariableType only specifies the minimum set of components that shall exist for each Variable of a VariableType.

5.7    Method NodeClass

Methods define callable functions. Methods are invoked using the Call Service defined in OPC 10000-4. Method invocations are not represented in the AddressSpace. Method invocations always run to completion and always return responses when complete. Methods are defined using the Method NodeClass, specified in Table 15.

Table 15 – Method NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

    Executable

M

Boolean

The Executable Attribute indicates if the Method is currently executable (“False” means not executable, “True” means executable).

The Executable Attribute does not take any user access rights into account, i.e. although the Method is executable this may be restricted to a certain user / user group.

    UserExecutable

M

Boolean

The UserExecutable Attribute indicates if the Method is currently executable taking user access rights into account (“False” means not executable, “True” means executable).

 

 

 

 

References

 

 

 

    HasProperty

0..*

 

HasProperty References identify the Properties for the Method.

    HasModellingRule

0..1

 

Methods can point to at most one ModellingRule Object using a HasModellingRule Reference (see 6.4.4 for details on ModellingRules).

    GeneratesEvent

0..*

 

GeneratesEvent References identify the type of Events that will be generated whenever the Method is called.

    AlwaysGeneratesEvent

0..*

 

AlwaysGeneratesEvent References identify the type of Events that shall be generated whenever the Method is called.

    <other References>

0..*

 

Methods may contain other References.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed.

    InputArguments

O

Argument[]

The InputArguments Property is used to specify the arguments that shall be used by a client when calling the Method.

    OutputArguments

O

Argument[]

The OutputArguments Property specifies the result returned from the Method call.

 

The Method NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2. The Method NodeClass defines no additional Attributes.

The Executable Attribute indicates whether the Method is executable, not taking user access rights into account. If the OPC UA Server cannot get the Executable information from the underlying system, it should state that it is executable. If a Method is called then the Server should transfer this request and return the corresponding StatusCode even if such a request is rejected. StatusCodes are defined in OPC 10000-4.

The UserExecutable Attribute indicates whether the Method is executable, taking user access rights into account. If the OPC UA Server cannot get any user rights related information from the underlying system, it should use the same value as used in the Executable Attribute. The UserExecutable Attribute can be set to “False”, even if the Executable Attribute is set to “True”, but it shall be set to “False” if the Executable Attribute is set to “False”. Clients cannot assume a Method can be executed based on the UserExecutable Attribute. It is possible that the Server may return an access denied error due to some Server specific change which was not reflected in the state of this Attribute at the time the Client accessed it.

Properties may be defined for Methods using HasProperty References. The Properties InputArguments and OutputArguments specify the input arguments and output arguments of the Method. Both contain an array of the DataType Argument as specified in 8.6. An empty array or a Property that is not provided indicates that there are no input arguments or output arguments for the Method.

The Property NodeVersion indicates the version of the Method. There are no additional Properties defined for Methods in this document. Additional parts of this series of standards may define additional Properties for Methods.

To specify its ModellingRule, a Method can use at most one HasModellingRule Reference pointing to a ModellingRule Object. ModellingRules are defined in 6.4.4.

GeneratesEvent References identify that Methods may generate an Event of the specified EventType or one of its subtypes for every call of the Method. A Server may generate one Event for each referenced EventType when a Method is successfully called.

AlwaysGeneratesEvent References identify that Methods will generate an Event of the specified EventType or one of its subtypes for every call of the Method. A Server shall always generate one Event for each referenced EventType when a Method is successfully called.

Servers should make GeneratesEvent References bidirectional References. However, it is allowed to be unidirectional when the Server is not able to expose the inverse direction pointing from the EventType to each Method generating the EventType.

GeneratesEvent References are optional, i.e. the call of a Method may produce Events of an EventType that is not referenced with a GeneratesEvent Reference by the Method.

Methods may use additional References to define relationships to other Nodes. No restrictions are placed on the types of References used or on the NodeClasses of the Nodes that may be referenced. However, restrictions may be defined by the ReferenceType excluding its use for Methods. Standard ReferenceTypes are described in Clause 7.

A Method shall always be the TargetNode of at least one HasComponent Reference. The SourceNode of these HasComponent References shall be an Object or an ObjectType. If a Method is called then the NodeId of one of those Nodes shall be put into the Call Service defined in OPC 10000-4 as parameter to detect the context of the Method operation.

If the Method is used as InstanceDeclaration (see 4.5) all Nodes referenced with forward hierarchical References shall have unique BrowseNames in the context of this Method.

5.8    DataTypes

5.8.1   DataType Model

The DataType Model is used to define simple and structured data types. Data types are used to describe the structure of the Value Attribute of Variables and their VariableTypes. Therefore each Variable and VariableType is pointing with its DataType Attribute to a Node of the DataType NodeClass as shown in Figure 10.

Figure14_

Figure 10 – Variables, VariableTypes and their DataTypes

In many cases, the NodeId of the DataType Node – the DataTypeId – will be well-known to Clients and Servers. Clause 8 defines DataTypes and OPC 10000-6 defines their DataTypeIds. In addition, other organizations may define DataTypes that are well-known in the industry. Well-known DataTypeIds provide for commonality across OPC UA Servers and allow Clients to interpret values without having to read the type description from the Server. Therefore, Servers may use well-known DataTypeIds without representing the corresponding DataType Nodes in their AddressSpaces.

In other cases, DataTypes and their corresponding DataTypeIds may be vendor-defined. Servers should attempt to expose the DataType Nodes and the information about the structure of those DataTypes for Clients to read, although this information might not always be available to the Server.

Figure 11 illustrates the Nodes used in the AddressSpace to describe the structure of a DataType. The DataType points to an Object of type DataTypeEncodingType. Each DataType can have several DataTypeEncoding, for example “Default”, “UA Binary” and “XML” encoding. Services in OPC 10000-4 allow Clients to request an encoding or choosing the “Default” encoding. Each DataTypeEncoding is used by exactly one DataType, that is, it is not permitted for two DataTypes to point to the same DataTypeEncoding.

Figure15_

Figure 11 – DataType Model

Since the NodeId of the DataTypeEncoding will be used in some Mappings to identify the DataType and it’s encoding as defined in OPC 10000-6, those NodeIds may also be well-known for well-known DataTypeIds.

5.8.2   Encoding Rules for different kinds of DataTypes

Different kinds of DataTypes are handled differently regarding their encoding and according to whether this encoding is represented in the AddressSpace.

Built-in DataTypes are a fixed set of DataTypes (see OPC 10000-6 for a complete list of Built-in DataTypes). They have no encodings visible in the AddressSpace since the encoding should be known to all OPC UA products. Examples of Built-in DataTypes are Int32 (see 8.26) and Double (see 8.12).

Simple DataTypes are subtypes of the Built-in DataTypes. They are handled on the wire like the Built-in DataType, i.e. they cannot be distinguished on the wire from their Built-in supertypes. Since they are handled like Built-in DataTypes regarding the encoding they cannot have encodings defined in the AddressSpace. Clients can read the DataType Attribute of a Variable or VariableType to identify the Simple DataType of the Value Attribute. An example of a Simple DataType is Duration. It is handled on the wire as a Double but the Client can read the DataType Attribute and thus interpret the value as defined by Duration (see 8.13).

Structured DataTypes are DataTypes that represent structured data and are not defined as Built-in DataTypes. Structured DataTypes inherit directly or indirectly from the DataType Structure defined in 8.33. Structured DataTypes may have several encodings and the encodings are exposed in the AddressSpace. How the encoding of Structured DataTypes is handled on the wire is defined in OPC 10000-6. The encoding of the Structured DataType is transmitted with each value, thus Clients are aware of the DataType without reading the DataType Attribute. The encoding has to be transmitted so the Client is able to interpret the data. An example of a Structured DataType is Argument (see 8.6).

Enumeration DataTypes are DataTypes that represent discrete sets of named values. Enumerations are always encoded as Int32 on the wire as defined in OPC 10000-6. Enumeration DataTypes inherit directly or indirectly from the DataType Enumeration defined in 8.14. Enumerations have no encodings exposed in the AddressSpace. To expose the human-readable representation of an enumerated value the DataType Node may have the EnumStrings Property that contains an array of LocalizedText. The Integer representation of the enumeration value points to a position within that array. EnumValues Property can be used instead of the EnumStrings to support integer representation of enumerations that are not zero-based or have gaps. It contains an array of a Structured DataType containing the integer representation as well as the human-readable representation. An example of an enumeration DataType containing a sparse list of Integers is NodeClass which is defined in 8.30.

In addition to the DataTypes described above, abstract DataTypes are also supported, which do not have any encodings and cannot be exchanged on the wire. Variables and VariableTypes use abstract DataTypes to indicate that their Value may be any one of the subtypes of the abstract DataType. An example of an abstract DataType is Integer which is defined in 8.24.

5.8.3   DataType NodeClass

The DataType NodeClass describes the syntax of a Variable Value. DataTypes are defined using the DataType NodeClass, as specified in Table 16.

Table 16 – DataType NodeClass

Name

Use

Data Type

Description

Attributes

 

 

 

    Base NodeClass Attributes

M

--

Inherited from the Base NodeClass. See 5.2.

    IsAbstract

M

Boolean

A boolean Attribute with the following values:

    TRUE          it is an abstract DataType.

     FALSE       it is not an abstract DataType.

    DataTypeDefinition

O

DataTypeDefinition

The DataTypeDefinition Attribute is used to provide the meta data and encoding information for custom DataTypes. The abstract DataTypeDefinition DataType is defined in 8.48.

Structure and Union DataTypes

The Attribute is mandatory for DataTypes derived from Structure and Union. For such DataTypes, the Attribute contains a structure of the DataType StructureDefinition. The StructureDefinition DataType is defined in 8.49. It is a subtype of DataTypeDefinition.

Enumeration and OptionSet DataTypes

The Attribute is mandatory for DataTypes derived from Enumeration, OptionSet and subtypes of UInteger representing an OptionSet. For such DataTypes, the Attribute contains a structure of the DataType EnumDefinition. The EnumDefinition DataType is defined in 8.50. It is a subtype of DataTypeDefinition.

 

 

 

 

References

 

 

 

    HasProperty

0..*

 

HasProperty References identify the Properties for the DataType.

    HasSubtype

0..*

 

HasSubtype References may be used to span a data type hierarchy.

    HasEncoding

0..*

 

HasEncoding References identify the encodings of the DataType represented as Objects of type DataTypeEncodingType.

Only concrete Structured DataTypes may use HasEncoding References. Abstract, Built-in, Enumeration, and Simple DataTypes are not allowed to be the SourceNode of a HasEncoding Reference.

Each concrete Structured DataType shall point to at least one DataTypeEncoding Object with the BrowseName “Default Binary” or “Default XML” having the NamespaceIndex 0. The BrowseName of the DataTypeEncoding Objects shall be unique in the context of a DataType, i.e. a DataType shall not point to two DataTypeEncodings having the same BrowseName.

 

 

 

 

Standard Properties

 

 

 

    NodeVersion

O

String

The NodeVersion Property is used to indicate the version of a Node.

The NodeVersion Property is updated each time a Reference is added or deleted to the Node the Property belongs to. Attribute value changes do not cause the NodeVersion to change. Clients may read the NodeVersion Property or subscribe to it to determine when the structure of a Node has changed. Clients shall not use the content for programmatic purposes except for equality comparisions.

    EnumStrings

O

LocalizedText[]

The EnumStrings Property only applies for Enumeration DataTypes. It shall not be applied for other DataTypes. If the EnumValues Property is provided, the EnumStrings Property shall not be provided.

Each entry of the array of LocalizedText in this Property represents the human-readable representation of an enumerated value. The Integer representation of the enumeration value points to a position of the array.

    EnumValues

O

EnumValueType[]

The EnumValues Property only applies for Enumeration DataTypes. It shall not be applied for other DataTypes. If the EnumStrings Property is provided, the EnumValues Property shall not be provided.

Using the EnumValues Property it is possible to represent Enumerations with integers that are not zero-based or have gaps (e.g. 1, 2, 4, 8, and 16).

Each entry of the array of EnumValueType in this Property represents one enumeration value with its integer notation, human-readable representation and help information.

    OptionSetValues

O

LocalizedText[]

The OptionSetValues Property only applies for OptionSet DataTypes and UInteger DataTypes.

An OptionSet DataType is used to represent a bit mask and the OptionSetValues Property contains the human-readable representation for each bit of the bit mask.

The OptionSetValues Property provides an array of LocalizedText containing the human-readable representation for each bit.

 

The DataType NodeClass inherits the base Attributes from the Base NodeClass defined in 5.2. The IsAbstract Attribute specifies if the DataType is abstract or not. Abstract DataTypes can be used in the AddressSpace, i.e. Variables and VariableTypes can point with their DataType Attribute to an abstract DataType. However, concrete values can never be of an abstract DataType and shall always be of a concrete subtype of the abstract DataType.

HasProperty References are used to identify the Properties of a DataType. The Property NodeVersion is used to indicate the version of the DataType. The Property EnumStrings contains human-readable representations of enumeration values and is only applied to Enumeration DataTypes. Instead of the EnumStrings Property an Enumeration DataType can also use the EnumValues Property to represent Enumerations with integer values that are not zero-based or containing gaps. There are no additional Properties defined for DataTypes in this standard. Additional parts of this series of standards may define additional Properties for DataTypes.

HasSubtype References may be used to expose a data type hierarchy in the AddressSpace. The semantic of subtyping is only defined to the point, that a Server may provide instances of the subtype instead of the DataType. Clients should not make any assumptions about any other semantic with that information. For example, it might not be possible to cast a value of one data type to its base data type. Servers need not provide HasSubtype References, even if their DataTypes span a type hierarchy. Some restrictions apply for subtyping enumeration DataTypes as defined in 8.14.

HasEncoding References point from the DataType to its DataTypeEncodings. Each concrete Structured DataType can point to many DataTypeEncodings, but each DataTypeEncoding shall belong to one DataType, that is, it is not permitted for two DataType Nodes to point to the same DataTypeEncoding Object using HasEncoding References.

An abstract DataType is not the SourceNode of a HasEncoding Reference. The DataTypeEncoding of an abstract DataType is provided by its concrete subtypes.

DataType Nodes shall not be the SourceNode of other types of References. However, they may be the TargetNode of other References.

5.8.4   DataTypeEncoding and Encoding Information

If a DataType Node is exposed in the AddressSpace, it shall provide its DataTypeEncodings using HasEncoding References. These References shall be bi-directional. Figure 12 provides an example how DataTypes are modelled in the AddressSpace.

Figure16_

Figure 12 – Example of DataType Modelling

The information on how to encode the DataType is provided in the Attribute DataTypeDefinition of the DataType Node. The content of this Attribute shall not be changed once it had been provided to Clients since Clients might persistently cache this information. If the encoding of a DataType needs to be changed conceptually a new DataType needs to be provided, meaning that a new NodeId shall be used for the DataType. Since Clients identify the DataType via the DataTypeEncodings, also the NodeIds for the DataTypeEncodings of the DataType shall be changed, when the encoding changes.

5.9    Summary of Attributes of the NodeClasses

Table 17 summarises all Attributes defined in this document and points out which NodeClasses use them either in an optional (O) or mandatory (M) way.

Table 17 – Overview of Attributes

Attribute

Variable

Variable Type

Object

Object Type

Reference Type

DataType

Method

View

AccessLevel

M

 

 

 

 

 

 

 

AccessLevelEx

O

 

 

 

 

 

 

 

ArrayDimensions

O

O

 

 

 

 

 

 

AccessRestrictions

O

O

O

O

O

O

O

O

BrowseName

M

M

M

M

M

M

M

M

ContainsNoLoops

 

 

 

 

 

 

 

M

DataType

M

M

 

 

 

 

 

 

DataTypeDefinition

 

 

 

 

 

O

 

 

Description

O

O

O

O

O

O

O

O

DisplayName

M

M

M

M

M

M

M

M

EventNotifier

 

 

M

 

 

 

 

M

Executable

 

 

 

 

 

 

M

 

Historizing

M

 

 

 

 

 

 

 

InverseName

 

 

 

 

O

 

 

 

IsAbstract

 

M

 

M

M

M

 

 

MinimumSamplingInterval

O

 

 

 

 

 

 

 

NodeClass

M

M

M

M

M

M

M

M

NodeId

M

M

M

M

M

M

M

M

RolePermissions

O

O

O

O

O

O

O

O

Symmetric

 

 

 

 

M

 

 

 

UserAccessLevel

M

 

 

 

 

 

 

 

UserExecutable

 

 

 

 

 

 

M

 

UserRolePermissions

O

O

O

O

O

O

O

O

UserWriteMask

O

O

O

O

O

O

O

O

Value

M

O

 

 

 

 

 

 

ValueRank

M

M

 

 

 

 

 

 

WriteMask

O

O

O

O

O

O

O

O

 

6    Type Model for ObjectTypes and VariableTypes

6.1    Overview

In the remainder of 6 the type model of ObjectTypes and VariableTypes is defined regarding subtyping and instantiation.

6.2    Definitions

6.2.1   InstanceDeclaration

An InstanceDeclaration is an Object, Variable or Method that references a ModellingRule with a HasModellingRule Reference and is the TargetNode of a hierarchical Reference from a TypeDefinitionNode or another InstanceDeclaration. The type of an InstanceDeclaration may be abstract, however the instance must be of a concrete type.

6.2.2   Instances without ModellingRules

If no ModellingRule exists then the Node is neither considered for instantiation of a type nor for subtyping.

If a Node referenced by a TypeDefinitionNode does not reference a ModellingRule it indicates that this Node only belongs to the TypeDefinitionNode and not to the instances. For example, an ObjectType Node may contain a Property that describes scenarios where the type could be used. This Property would not be considered when creating instances of the type. This is also true for subtyping, that is, subtypes of the type definition would not inherit the referenced Node.

6.2.3   InstanceDeclarationHierarchy

The InstanceDeclarationHierarchy of a TypeDefinitionNode contains the TypeDefinitionNode and all InstanceDeclarations that are directly or indirectly referenced from the TypeDefinitionNode using forward hierarchical References.

6.2.4   Similar Node of InstanceDeclaration

A similar Node of an InstanceDeclaration is a Node that has the same BrowseName and NodeClass as the InstanceDeclaration and in cases of Variables and Objects the same TypeDefinitionNode or a subtype of it.

6.2.5   BrowsePath

All targets of forward hierarchical References from a TypeDefinitionNode shall have a BrowseName that is unique within the TypeDefinitionNode. The same restriction applies to the targets of forward hierarchical References from any InstanceDeclaration. This means that any InstanceDeclaration within the InstanceDeclarationHierarchy can be uniquely identified by a sequence of BrowseNames. This sequence of BrowseNames is called a BrowsePath.

6.2.6   Attribute Handling of InstanceDeclarations

Some restrictions exist regarding the Attributes of InstanceDeclarations when the InstanceDeclaration is overridden or instantiated. The BrowseName and the NodeClass shall never change and always be the same as the original InstanceDeclaration.

In addition, the rules defined in 6.2.7 apply for InstanceDeclarations of the NodeClass Variable.

6.2.7   Attribute Handling of Variable and VariableTypes

Some restrictions exist regarding the Attributes of a VariableType or a Variable used as an InstanceDeclaration with regard to the data type of the Value Attribute.

When a Variable used as InstanceDeclaration or a VariableType is overridden or instantiated the following rules apply:

a)    The DataType Attribute can only be changed to a new DataType if the new DataType is a subtype of the DataType originally used.

b)   The ValueRank Attribute may only be further restricted

1)   ‘Any’ may be set to any other value;

2)   ‘ScalarOrOneDimension’ may be set to ‘Scalar’ or ‘OneDimension’;

3)   ‘OneOrMoreDimensions’ may be set to a concrete number of dimensions (value > 0).

4)   All other values of this Attribute shall not be changed.

c)    The ArrayDimensions Attribute may be added if it was not provided or when modifying the value of an entry in the array from 0 to a different value. All other values in the array shall remain the same.

6.2.8   NodeIds of InstanceDeclarations

InstanceDeclarations are identified by their BrowsePath. Different Servers might use different NodeIds for the InstanceDeclarations of common TypeDefinitionNodes, unless the definition of the TypeDefinitionNode already defines a NodeId for the InstanceDeclaration. All TypeDefinitionNodes defined in OPC 10000-5 already define the NodeIds for their InstanceDeclarations and therefore shall be used in all Servers.

6.3    Subtyping of ObjectTypes and VariableTypes

6.3.1   Overview

The HasSubtype ReferenceType defines subtypes of types. Subtyping can only occur between Nodes of the same NodeClass. Rules for subtyping ReferenceTypes are described in 5.3.3.3. There is no common definition for subtyping DataTypes, as described in 5.8.3. The remainder of 6.3 specify subtyping rules for single inheritance on ObjectTypes and VariableTypes.

6.3.2   Attributes

Subtypes inherit the parent type’s Attribute values, except for the NodeId. Inherited Attribute values may be overridden by the subtype, the BrowseName and DisplayName values should be overridden. Special rules apply for some Attributes of VariableTypes as defined in 6.2.7. Optional Attributes, not provided by the parent type, may be added to the subtype.

6.3.3   InstanceDeclarations

6.3.3.1   Overview

Subtypes inherit the fully-inherited parent type’s InstanceDeclarations.

As long as those InstanceDeclarations are not overridden they are not referenced by the subtype. InstanceDeclarations can be overridden by adding References, changing References to reference different Nodes, changing References to be subtypes of the original ReferenceType, changing values of the Attributes or adding optional Attributes. In order to get the full information about a subtype, the inherited InstanceDeclarations have to be collected from all types that can be found by recursively following the inverse HasSubtype References from the subtype. This collection of InstanceDeclarations is called the fully-inherited InstanceDeclarationHierarchy of a subtype.

The remainder of 6.3.3 define how to construct the fully-inherited InstanceDeclarationHierarchy and how InstanceDeclarations can be overridden.

6.3.3.2   Fully-inherited InstanceDeclarationHierarchy

An instance of a TypeDefinitionNode is described by the fully-inherited InstanceDeclaration­Hierarchy of the TypeDefinitionNode. The fully-inherited InstanceDeclarationHierarchy can be created by starting with the InstanceDeclarationHierarchy of the TypeDefinitionNode and merging the fully-inherited InstanceDeclarationHierarchy of its parent type.

The process of merging InstanceDeclarationHierarchies is straightforward and can be illustrated with the example shown in Figure 13 which specifies a TypeDefinitionNode “BetaType” which is a subtype of “AlphaType”. The name in each box is the BrowseName and the number is the NodeId.

Figure17_

Figure 13 – Subtyping TypeDefinitionNodes

An InstanceDeclarationHierarchy can be fully described as a table of Nodes identified by their BrowsePaths with a corresponding table of References. The InstanceDeclarationHierarchy for “BetaType” is described in Table 18 where the top half of the table is the table of Nodes and the bottom half is the table of References (the HasModellingRule references have been omitted from the table for the sake of clarity; all Nodes except for 1, 6, and 5 have ModellingRules). All InstanceDeclarations of the InstanceDeclarationHierarchy and all Nodes referenced with a non-hierarchical Reference from such an InstanceDeclaration are added to the table. Hierarchical References to Nodes without a ModellingRule are not considered.

Table 18 – The InstanceDeclarationHierarchy for BetaType

BrowsePath

NodeId

 

 

/

6

 

 

/F

7

 

 

/B

8

 

 

/F/H

9

 

 

/B/J

10

 

 

/B/H

9

 

 

 

Source Path

ReferenceType

Target Path

TargetNodeId

/

HasComponent

/F

-

/

HasComponent

/B

-

/

Z

/B

-

/

HasTypeDefinition

-

BetaType

/F

HasComponent

/F/H

-

/F

HasTypeDefinition

-

BaseObjectType

/B

HasProperty

/B/J

-

/B

HasTypeDefinition

-

BaseObjectType

/F/H

HasTypeDefinition

-

PropertyType

/B/J

HasTypeDefinition

-

PropertyType

/B

HasComponent

/B/H

-

/B/H

HasTypeDefinition

-

BaseDataVariableType

 

Multiple BrowsePaths to the same Node shall be treated as separate Nodes. An Instance may provide different Nodes for each BrowsePath.

The fully-inherited InstanceDeclarationHierarchy for “BetaType” can now be constructed by merging the InstanceDeclarationHierarchy for “AlphaType”. The result is shown in Table 19 where the entries added from “AlphaType” are shaded with grey.

Table 19 – The Fully-Inherited InstanceDeclarationHierarchy for BetaType

BrowsePath

NodeId

 

 

/

6

 

 

/F

7

 

 

/B

8

 

 

/F/H

9

 

 

/B/J

10

 

 

/B/H

9

 

 

/B/D

4

 

 

/C

3

 

 

 

Source Path

ReferenceType

Target Path

TargetNodeId

/

HasComponent

/F

-

/

HasComponent

/B

-

/

Z

/B

-

/

HasTypeDefinition

-

BetaType

/F

HasComponent

/F/H

-

/F

HasTypeDefinition

-

BaseObjectType

/B

HasProperty

/B/J

-

/B

HasTypeDefinition

-

BaseObjectType

/F/H

HasTypeDefinition

-

PropertyType

/B/J

HasTypeDefinition

-

PropertyType

/B

HasComponent

/B/H

-

/B/H

HasTypeDefinition

-

BaseDataVariableType

/

HasNotifier

/B

-

/B

HasProperty

/B/D

-

/

HasComponent

/C

-

/

Y

/C

-

/C

HasTypeDefinition

-

BaseDataVariableType

/B/D

HasTypeDefinition

-

PropertyType

/B/D

X

/C

-

 

The BrowsePath “/B” already exists in the table so it does not need to be added. However, the HasNotifier reference from “/” to “/B” does not exist and was added.

The Nodes and References defined in Table 19 can be used to create the fully-inherited InstanceDeclarationHierarchy shown in Figure 14. The fully-inherited InstanceDeclarationHierarchy contains all necessary information about a TypeDefinitionNode regarding its complex structure without needing any additional information from its supertypes.

Figure18_

Figure 14 – The Fully-Inherited InstanceDeclarationHierarchy for BetaType

6.3.3.3   Overriding InstanceDeclarations

A subtype overrides an InstanceDeclaration by specifying an InstanceDeclaration with the same BrowsePath. An overridden InstanceDeclaration shall have the same NodeClass and BrowseName. The TypeDefinitionNode of the overridden InstanceDeclaration shall be the same or a subtype of the TypeDefinitionNode specified in the supertype.

When overriding an InstanceDeclaration it is necessary to provide hierarchical References that link the new Node back to the subtype (the References are used to determine the BrowsePath of the Node).

It is only possible to override InstanceDeclarations that are directly referenced from the TypeDefinitionNode. If an indirect referenced InstanceDeclaration, such as “J” in Figure 14, has to be overridden, then the directly referenced InstanceDeclarations that includes “J”, in that case “B”, have to be overridden first and then “J” can be overridden in a second step.

A Reference is replaced if it goes between two overridden Nodes and has the same ReferenceType as a Reference defined in the supertype. The Reference specified in the subtype may be a subtype of the ReferenceType used in the parent type.

Any non-hierarchical References specified for the overridden InstanceDeclaration are treated as new References unless the ReferenceType only allows a single Reference per SourceNode. If this situation exists the subtype can change the target of the Reference but the new target shall have the same NodeClass and for Objects and Variables also the same type or a subtype of the type specified in the parent.

The overriding Node may specify new values for the Node Attributes other than the NodeClass or BrowseName, however, the restrictions on Attributes specified in 6.2.6 apply. Any Attribute provided by the overridden InstanceDeclaration has to be provided by the overriding InstanceDeclaration, additional optional Attributes may be added.

The ModellingRule of the overriding InstanceDeclaration may be changed as defined in 6.4.4.3.

Each overriding InstanceDeclaration needs its own HasModellingRule and HasTypeDefinition References, even if they have not been changed.

A subtype should not override a Node unless it needs to change it.

The semantics of certain TypeDefinitionNodes and ReferenceTypes may impose additional restrictions with regard to overriding Nodes.

6.4    Instances of ObjectTypes and VariableTypes

6.4.1   Overview

Any Instance of a TypeDefinitionNode will be the root of a hierarchy which mirrors the InstanceDeclarationHierarchy for the TypeDefinitionNode. Each Node in the hierarchy of the Instance will have a BrowsePath which may be the same as the BrowsePath for one of the InstanceDeclarations in the hierarchy of the TypeDefinitionNode. The InstanceDeclaration with the same BrowsePath is called the InstanceDeclaration for the Node. If a Node has an InstanceDeclaration then it shall have the same BrowseName and NodeClass as the InstanceDeclaration and, in cases of Variables and Objects, the same TypeDefinitionNode or a subtype of it.

Instances may reference several Nodes with the same BrowsePath. Clients that need to distinguish between the Nodes based on the InstanceDeclarationHierarchy and the Nodes that are not based on the InstanceDeclarationHierarchy can accomplish this using the TranslateBrowsePathsToNodeIds service defined in OPC 10000-4.

6.4.2   Creating an Instance

Instances inherit the initial values for the Attributes that they have in common with the TypeDefinitionNode from which they are instantiated, with the exceptions of the NodeClass and NodeId.

When a Server creates an instance of a TypeDefinitionNode it shall create the same hierarchy of Nodes beneath the new Object or Variable depending on the ModellingRule of each InstanceDeclaration. Standard ModellingRules are defined in 6.4.4.5. The Nodes within the newly created hierarchy may be copies of the InstanceDeclarations, the InstanceDeclaration itself or another Node in the AddressSpace that has the same TypeDefinitionNode and BrowseName. If new copies are created, then the Attribute values of the InstanceDeclarations are used as the initial values.

Figure 15 provides a simple example of a TypeDefinitionNode and an Instance. Nodes referenced by the TypeDefinitionNode without a ModellingRule do not appear in the instance. Instances may have children with duplicate BrowseNames; however, only one of those children will correspond to the InstanceDeclaration.

 

Figure19_

Figure 15 – An Instance and its TypeDefinitionNode

It is up to the Server to decide which InstanceDeclarations appear in any single instance. In some cases, the Server will not define the entire instance and will provide remote references to Nodes in another Server. The ModellingRules described in 6.4.4.5 allow Servers to indicate that some Nodes are always present; however, the Client shall be prepared for the case where the Node exists in a different Server.

A Client can use the information of TypeDefinitionNodes to access Nodes which are in the hierarchy of the instance. It shall pass the NodeId of the instance and the BrowsePath of the child Nodes based on the TypeDefinitionNode to the TranslateBrowsePathsToNodeIds service (see OPC 10000-4). This Service returns the NodeId for each of the child Nodes. If a child Node exists then the BrowseName and NodeClass shall match the InstanceDeclaration. In the case of Objects or Variables, also the TypeDefinitionNode shall either match or be a subtype of the original TypeDefinitionNode.

6.4.3   Constraints on an Instance

Objects and Variables may change their Attribute values after being created. Special rules apply for some Attributes as defined in 6.2.6.

Additional References may be added to the Nodes, and References may be deleted as long as the ModellingRules defined on the InstanceDeclarations of the TypeDefinitionNode are still fulfilled.

For Variables and Objects the HasTypeDefinition Reference shall always point to the same TypeDefinitionNode as the InstanceDeclaration or a subtype of it.

If two InstanceDeclarations of the fully-inherited InstanceDeclarationHierarchy have been connected directly with several References, all those References shall connect the same Nodes. An example is given in Figure 16. The instances A1 and A2 are allowed since B1 references the same Node with both References, whereas A3 is not allowed since two different Nodes are referenced. Note that this restriction only applies for directly connected Nodes. For example, A2 references a C1 directly and a different C1 via B1.

Figure20_

Figure 16 – Example for several References between InstanceDeclarations

6.4.4   ModellingRules

6.4.4.1   General

For a definition of ModellingRules, see 6.4.4.5. Other parts of this series of standards may define additional ModellingRules. ModellingRules are an extendable concept in OPC UA; therefore vendors may define their own ModellingRules.

Note that the ModellingRules defined in this standard do not define how to deal with non-hierarchical References between InstanceDeclarations, i.e. it is Server-specific if those References exist in an instance hierarchy or not. Other ModellingRules may define behaviour for non-hierarchical References between InstanceDeclaration as well.

ModellingRules are represented in the AddressSpace as Objects of the ObjectType ModellingRuleType. There are some Properties defining common semantic of ModellingRules. This edition of this standard only specifies one Property for ModellingRules. Future editions may define additional Properties for ModellingRules. OPC 10000-5 specifies the representation of the ModellingRule Objects, their Properties and their type in the AddressSpace. The semantic of the Properties for ModellingRules is defined in 6.4.4.2.

Subclause 6.4.4.4 defines how the ModellingRule may be changed when instantiating InstanceDeclarations with respect to the Properties. Subclause 6.4.4.3 defines how the ModellingRule may be changed when overriding InstanceDeclarations in subtypes with respect to the Properties.

6.4.4.2   Properties describing ModellingRules

6.4.4.2.1   NamingRule

NamingRule is a mandatory Property of a ModellingRule. It specifies the purpose of an InstanceDeclaration. Each InstanceDeclaration references a ModellingRule and thus the NamingRule is defined per InstanceDeclaration.

Three values are allowed for the NamingRule of a ModellingRule: Optional, Mandatory, and Constraint.

The following semantic is valid for the entire life-time of an instance that is based on a TypeDefinitionNode having an InstanceDeclaration.

For an instance A1 of a TypeDefinitionNode AlphaType with an InstanceDeclaration B1 having a ModellingRule using the NamingRule Optional the following rule applies: For each BrowsePath from AlphaType to B1 the instance A1 may or may not have a similar Node (see 6.2.4) for B1 with the same BrowsePath. If such a Node exists then the TranslateBrowsePathsToNodeIds Service (see OPC 10000-4) returns this Node as the first entry in the list.

For an instance A1 of a TypeDefinitionNode AlphaType with an InstanceDeclaration B1 having a ModellingRule using the NamingRule Mandatory the following rule applies: For each BrowsePath from AlphaType to B1 the instance A1 shall have a similar Node (see 6.2.4) for B1 using the same BrowsePath if all Nodes of the BrowsePath exist. For example, if a Node in the BrowsePath has a NamingRule Optional and is omitted in the instance, then all children of this Node would also be omitted, independent of their ModellingRules.

If an InstanceDeclaration has a ModellingRule using the NamingRule Constraint it identifies that the BrowseName of the InstanceDeclaration is of no significance but other semantic is defined with the ModellingRule. The TranslateBrowsePathsToNodeIds Service (see OPC 10000-4) can typically not be used to access instances based on those InstanceDeclarations.

6.4.4.3   Subtyping Rules for Properties of ModellingRules

It is allowed that subtypes override ModellingRules on their InstanceDeclarations. As a general rule for subtyping, constraints shall only be tightened, not loosened. Therefore, it is not allowed to specify on the supertype that an instance shall exist with the name (NamingRule Mandatory) and on the subtype make this optional (NamingRule Optional).
Table 20 specifies the allowed changes on the Properties when exchanging the ModellingRules in the subtype.

Table 20 – Rule for ModellingRules Properties when Subtyping

 

Value on supertype

Value on subtype

NamingRule

Mandatory

Mandatory

NamingRule

Optional

Mandatory or Optional

NamingRule

Constraint

Constraint

 

6.4.4.4   Instantiation Rules for Properties of ModellingRules

There are two different use cases when creating an instance ‘A’ based on a TypeDefinitionNode ‘A_Type’. Either ‘A’ is used as normal instance or it is used as InstanceDeclaration of another TypeDefinitionNode.

In the first case, it is not required that newly created or referenced instances based on InstanceDeclarations have a ModellingRule, however, it is allowed that they have any ModellingRule independent of the ModellingRule of their InstanceDeclaration.

In Figure 17 an example is given. The instances A1, A2, and A3 are all valid instances of Type_A, although B of A1 has no ModellingRule and B of A3 has a different ModellingRule than B of Type_A.

Figure21_

Figure 17 – Example on changing instances based on InstanceDeclarations

In the second case, all instances that are referenced directly or indirectly from ‘A’ based on InstanceDeclarations of ‘A_Type’ initially maintain the same ModellingRule as their InstanceDeclarations. The ModellingRules may be updated; the allowed changes to the ModellingRules of these Nodes are the same as those defined for subtyping in 6.4.4.3.

In Figure 18 an example of such a scenario is given. Type_B uses an InstanceDeclaration based on Type_A (upper part of the Figure). Later on the ModellingRule of the InstanceDeclaration A1 is changed (lower part of the Figure). A1 has become the NamingRule of Mandatory (changed from Optional).

Figure22_

Figure 18 – Example on changing InstanceDeclarations based
on an InstanceDeclaration

6.4.4.5   Standard ModellingRules

6.4.4.5.1   Titles of Standard ModellingRules

The remainder of 6.4.4.5 defines ModellingRules. In Table 21 the Properties of those ModellingRules are summarized.

Table 21 – Properties of ModellingRules

Title

NamingRule

Mandatory

Mandatory

Optional

Optional

ExposesItsArray

Constraint

OptionalPlaceholder

Constraint

MandatoryPlaceholder

Constraint

 

6.4.4.5.2   Mandatory

An InstanceDeclaration marked with the ModellingRule Mandatory fulfils exactly the semantic defined for the NamingRule Mandatory. That means that for each existing BrowsePath on the instance a similar Node shall exist, but it is not defined whether a new Node is created or an existing Node is referenced.

For example, the TypeDefinitionNode of a functional block “AI_BLK_TYPE” will have a setpoint “SP1”. An instance of this type “AI_BLK_1” will have a newly-created setpoint “SP1” as a similar Node to the InstanceDeclaration SP1. Figure 19 illustrates the example.

Figure23_

Figure 19 – Use of the Standard ModellingRule Mandatory

In 6.4.4.5.3 a complex example combining the Mandatory and Optional ModellingRules is given.

6.4.4.5.3   Optional

An InstanceDeclaration marked with the ModellingRule Optional fulfils exactly the semantic defined for the NamingRule Optional. That means that for each existing BrowsePath on the instance a similar Node may exist, but it is not defined whether a new Node is created or an existing Node is referenced.

In Figure 20 an example using the ModellingRules Optional and Mandatory is shown. The example contains an ObjectType Type_A and all valid combinations of instances named A1 to A13. Note that if the optional B is provided, the mandatory E has to be provided as well, otherwise not. F is referenced by C and D. On the instance, this can be the same Node or two different Nodes with the same BrowseName (similar Node to InstanceDeclaration F). Not considered in the example is if the instances have ModellingRules or not. It is assumed that each F is similar to the InstanceDeclaration F, etc.

If there would be a non-hierarchical Reference between E and F in the InstanceDeclaration­Hierarchy, it is not specified if it occurs in the instance hierarchy or not. In the case of A10, there could be a reference from E to one F but not to the other F, or to both or none of them.

Figure24_

Figure 20 – Example using the Standard ModellingRules Optional and Mandatory

6.4.4.5.4   ExposesItsArray

The ExposesItsArray ModellingRule exposes a special semantic on VariableTypes having a single- or multidimensional array as the data type. It indicates that each value of the array will also be exposed as a Variable in the AddressSpace.

The ExposesItsArray ModellingRule can only be applied on InstanceDeclarations of NodeClass Variable that are part of a VariableType having a single- or multidimensional array as its data type.

The Variable A having this ModellingRule shall be referenced by a forward hierarchical Reference from a VariableType B. B shall have a ValueRank value that is equal to or larger than zero. A should have a data type that reflects at least parts of the data that is managed in the array of B. Each instance of B shall reference one instance of A for each of its array elements. The used Reference shall be of the same type as the hierarchical Reference that connects B with A or a subtype of it. If there are more than one forward hierarchical References between A and B, then all instances based on B shall be referenced with all those References.

Figure 21 gives an example. A is an instance of Type_A having two entries in its value array. Therefore it references two instances of the same type as the InstanceDeclaration ArrayExpose. The BrowseNames of those instances are not defined by the ModellingRule. In general, it is not possible to get a Variable representing a specific entry in the array (e.g. the second). Clients will typically either get the array or access the Variables directly, so there is no need to provide that information.

Figure25_

Figure 21 – Example on using ExposesItsArray

It is allowed to reference A by other InstanceDeclarations as well. Those References have to be reflected on each instance based on A.

Figure 22 gives an example. The Property EUUnit is referenced by ArrayExpose and therefore each instance based on ArrayExpose references the instance based on the InstanceDeclaration EUUnit.

Figure26_

Figure 22 – Complex example on using ExposesItsArray

6.4.4.5.5   OptionalPlaceholder

For Object and Variable the intention of the ModellingRule OptionalPlaceholder is to expose the information that a complex TypeDefinition expects from instances of the TypeDefinition to add instances with specific References without defining BrowseNames for the instances. For example, a Device might have a Folder for DeviceParameters, and the DeviceParameters should be connected with a HasComponent Reference. However, the names of the DeviceParameters are specific to the instances. The example is shown in Figure 23, where an instance Device A adds two DeviceParameters in the Folder.

Figure27_

Figure 23 – Example using OptionalPlaceholder with an Object and Variable

The ModellingRule OptionalPlaceholder adds no additional constraints on instances of the TypeDefinition. It just provides useful information when exposing a TypeDefinition. When the InstanceDeclaration is complex, i.e. it references other InstanceDeclarations with hierarchical References, these InstanceDeclarations are not further considered for instantiating the TypeDefinition.

It is recommended that the BrowseName and the DisplayName of InstanceDeclarations having the OptionalPlaceholder ModellingRule should be enclosed within angle brackets.

When overriding the InstanceDeclaration, the ModellingRule shall remain OptionalPlaceholder.

For Methods, the ModellingRule OptionalPlaceholder is used to define the BrowseName where subtypes and instances provide more information. The Method definition with the OptionalPlaceholder only defines the BrowseName. An instance or subtype defines the InputArguments and OutputArguments. A subtype shall also change the ModellingRule to Optional or Mandatory. The Method is optional for instances. For example, a Device might have a Method to perform calibration however the specific arguments for the Method depend on the instance of the Device. In this example Device A does not implement the Method, Device B implements the Method with no arguments and Device C implements the Method accepting a mode argument to select how the calibration is to be performed. The example is shown in Figure 24.

Figure28_

Figure 24 – Example using OptionalPlaceholder with a Method

6.4.4.5.6   MandatoryPlaceholder

For Object and Variable the ModellingRule MandatoryPlaceholder has a similar intention as the ModellingRule OptionalPlaceholder. It exposes the information that a TypeDefinition expects of instances of the TypeDefinition to add instances defined by the InstanceDeclaration. However, MandatoryPlaceholder requires that at least one of those instances shall exist.

For example, when the DeviceType requires that at least one DeviceParameter shall exist without specifying the BrowseName for it, it uses MandatoryPlaceholder as shown in
Figure 25. Device A is a valid instance as it has the required DeviceParameter. Device B is not valid as it uses the wrong ReferenceType to reference a DeviceParameter (Organizes instead of HasComponent) and Device C is not valid because it does not provide a DeviceParameter at all.

Figure29_

Figure 25 – Example on using MandatoryPlaceholder for Object and Variable

The ModellingRule MandatoryPlaceholder requires that each instance provides at least one instance with the TypeDefinition of the InstanceDeclaration or a subtype, and is referenced with the same ReferenceType or a subtype as the InstanceDeclaration. It does not require a specific BrowseName and thus cannot be used for the TranslateBrowsePathsToNodeIds Service (see OPC 10000-4).

When the InstanceDeclaration is complex, i.e. it references other InstanceDeclarations with hierarchical References, these InstanceDeclarations are not further considered for instantiating the TypeDefinition.

It is recommended that the BrowseName and the DisplayName of InstanceDeclarations having the MandatoryPlaceholder ModellingRule should be enclosed within angle brackets.

When overriding the InstanceDeclaration, the ModellingRule shall remain MandatoryPlaceholder.

For Methods, the ModellingRule MandatoryPlaceholder is used to define the BrowseName where subtypes and instances provide more information. The Method definition with the MandatoryPlaceholder only defines the BrowseName. An instance or subtype defines the InputArguments and OutputArguments. A subtype shall also change the ModellingRule to Mandatory. The Method is mandatory for instances.

6.5    Changing Type Definitions that are already used

There is no behaviour specified regarding subtypes and instances when changing ObjectTypes and VariableTypes. It is Server-dependent, if those changes are reflected on the subtypes and instances of the types. However, all constraints defined for subtypes and instances have to be fulfilled. For example, it is not allowed to add a Property using the ModellingRule Mandatory on a type if instances of this type exist without the Property. In that case, the Server either has to add the Property to all instances of the type or adding the Property on the type has to be rejected.

7    Standard ReferenceTypes

7.1    General

This standard defines ReferenceTypes as an inherent part of the OPC UA Address Space Model. Figure 26 informally describes the hierarchy of these ReferenceTypes. Other parts of this series of standards may specify additional ReferenceTypes. The remainder of 7 defines the ReferenceTypes. OPC 10000-5 defines their representation in the AddressSpace.

Figure30_

Figure 26 – Standard ReferenceType Hierarchy

7.2    References ReferenceType

The References ReferenceType is an abstract ReferenceType; only subtypes of it can be used.

There is no semantic associated with this ReferenceType. This is the base type of all ReferenceTypes. All ReferenceTypes shall be a subtype of this base ReferenceType – either direct or indirect. The main purpose of this ReferenceType is allowing simple filter and queries in the corresponding Services of OPC 10000-5.

There are no constraints defined for this abstract ReferenceType.

7.3    HierarchicalReferences ReferenceType

The HierarchicalReferences ReferenceType is an abstract ReferenceType; only subtypes of it can be used.

The semantic of HierarchicalReferences is to denote that References of HierarchicalReferences span a hierarchy. It means that it may be useful to present Nodes related with References of this type in a hierarchical-like way. HierarchicalReferences does not forbid loops. For example, starting from Node “A” and following HierarchicalReferences it may be possible to browse to Node “A”, again.

It is not permitted to have a Property as SourceNode of a Reference of any subtype of this abstract ReferenceType.

It is not allowed that the SourceNode and the TargetNode of a Reference of the ReferenceType HierarchicalReferences are the same, that is, it is not allowed to have self-references using HierarchicalReferences.

7.4    NonHierarchicalReferences ReferenceType

The NonHierarchicalReferences ReferenceType is an abstract ReferenceType; only subtypes of it can be used.

The semantic of NonHierarchicalReferences is to denote that its subtypes do not span a hierarchy and should not be followed when trying to present a hierarchy. To distinguish hierarchical and non-hierarchical References, all concrete ReferenceTypes shall inherit from either hierarchical References or non-hierarchical References, either direct or indirect.

There are no constraints defined for this abstract ReferenceType.

7.5    HasChild ReferenceType

The HasChild ReferenceType is an abstract ReferenceType; only subtypes of it can be used. It is a subtype of HierarchicalReferences.

The semantic is to indicate that References of this type span a non-looping hierarchy.

Starting from Node “A” and only following References of the subtypes of the HasChild ReferenceType it shall never be possible to return to “A”. But it is allowed that following the References there may be more than one path leading to another Node “B”.

7.6    Aggregates ReferenceType

The Aggregates ReferenceType is an abstract ReferenceType; only subtypes of it can be used. It is a subtype of HasChild.

The semantic is to indicate a part (the TargetNode) belongs to the SourceNode. It does not specify the ownership of the TargetNode.

There are no constraints defined for this abstract ReferenceType.

7.7    HasComponent ReferenceType

The HasComponent ReferenceType is a concrete ReferenceType that can be used directly. It is a subtype of the Aggregates ReferenceType.

The semantic is a part-of relationship. The TargetNode of a Reference of the HasComponent ReferenceType is a part of the SourceNode. This ReferenceType is used to relate Objects or ObjectTypes with their containing Objects, DataVariables, and Methods. This ReferenceType is also used to relate complex Variables or VariableTypes with their DataVariables.

Like all other ReferenceTypes, this ReferenceType does not specify anything about the ownership of the parts, although it represents a part-of relationship semantic. That is, it is not specified if the TargetNode of a Reference of the HasComponent ReferenceType is deleted when the SourceNode is deleted.

The TargetNode of this ReferenceType shall be a Variable, an Object or a Method.

If the TargetNode is a Variable, the SourceNode shall be an Object, an ObjectType, a DataVariable or a VariableType. By using the HasComponent Reference, the Variable is defined as DataVariable.

If the TargetNode is an Object or a Method, the SourceNode shall be an Object or ObjectType.

7.8    HasProperty ReferenceType

The HasProperty ReferenceType is a concrete ReferenceType that can be used directly. It is a subtype of the Aggregates ReferenceType.

The semantic is to identify the Properties of a Node. Properties are described in 4.4.2.

The SourceNode of this ReferenceType can be of any NodeClass. The TargetNode shall be a Variable. By using the HasProperty Reference, the Variable is defined as Property. Since Properties shall not have Properties, a Property shall never be the SourceNode of a HasProperty Reference.

7.9    HasOrderedComponent ReferenceType

The HasOrderedComponent ReferenceType is a concrete ReferenceType that can be used directly. It is a subtype of the HasComponent ReferenceType.

The semantic of the HasOrderedComponent ReferenceType – besides the semantic of the HasComponent ReferenceType – is that when browsing from a Node and following References of this type or its subtype all References are returned in the Browse Service defined in OPC 10000-4 in a well-defined order. The order is Server-specific, but the Client can assume that the Server always returns them in the same order.

There are no additional constraints defined for this ReferenceType.

7.10    HasSubtype ReferenceType

The HasSubtype ReferenceType is a concrete ReferenceType that can be used directly. It is a subtype of the HasChild ReferenceType.

The semantic of this ReferenceType is to express a subtype relationship of types. It is used to span the ReferenceType hierarchy, whose semantic is specified in 5.3.3.3; a DataType hierarchy is specified in 5.8.3, and other subtype hierarchies are specified in Clause 6.

The SourceNode of References of this type shall be an ObjectType, a VariableType, a DataType or a ReferenceType and the TargetNode shall be of the same NodeClass as the SourceNode. Each ReferenceType shall be the TargetNode of at most one Reference of type HasSubtype.

7.11    Organizes ReferenceType

The Organizes ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of HierarchicalReferences.

The semantic of this ReferenceType is to organise Nodes in the AddressSpace. It can be used to span multiple hierarchies independent of any hierarchy created with the non-looping Aggregates References.

The SourceNode of References of this type shall be an Object or a View. If it is an Object then it should be an Object of the ObjectType FolderType or one of its subtypes (see 5.5.3).

The TargetNode of this ReferenceType can be of any NodeClass.

7.12    HasModellingRule ReferenceType

The HasModellingRule ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of NonHierarchicalReferences.

The semantic of this ReferenceType is to bind the ModellingRule to an Object, Variable or Method. The ModellingRule mechanisms are described in 6.4.4.

The SourceNode of this ReferenceType shall be an Object, Variable or Method. The TargetNode shall be an Object of the ObjectType “ModellingRule” or one of its subtypes.

Each Node shall be the SourceNode of at most one HasModellingRule Reference.

7.13    HasTypeDefinition ReferenceType

The HasTypeDefinition ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of NonHierarchicalReferences.

The semantic of this ReferenceType is to bind an Object or Variable to its ObjectType or VariableType, respectively. The relationships between types and instances are described in 4.5.

The SourceNode of this ReferenceType shall be an Object or Variable. If the SourceNode is an Object, then the TargetNode shall be an ObjectType; if the SourceNode is a Variable, then the TargetNode shall be a VariableType.

Each Variable and each Object shall be the SourceNode of exactly one HasTypeDefinition Reference.

7.14    HasEncoding ReferenceType

The HasEncoding ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of NonHierarchicalReferences.

The semantic of this ReferenceType is to reference DataTypeEncodings of a subtype of the Structure DataType.

The SourceNode of References of this type shall be a subtype of the Structure DataType.

The TargetNode of this ReferenceType shall be an Object of the ObjectType DataTypeEncodingType or one of its subtypes (see 5.8.4).

7.15    GeneratesEvent

The GeneratesEvent ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of NonHierarchicalReferences.

The semantic of this ReferenceType is to identify the types of Events instances of ObjectTypes or VariableTypes may generate and Methods may generate on each Method call.

The SourceNode of References of this type shall be an ObjectType, a VariableType or a Method.

The TargetNode of this ReferenceType shall be an ObjectType representing EventTypes, that is, the BaseEventType or one of its subtypes.

7.16    AlwaysGeneratesEvent

The AlwaysGeneratesEvent ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of GeneratesEvent.

The semantic of this ReferenceType is to identify the types of Events Methods have to generate on each Method call.

The SourceNode of References of this type shall be a Method.

The TargetNode of this ReferenceType shall be an ObjectType representing EventTypes, that is, the BaseEventType or one of its subtypes.

7.17    HasEventSource

The HasEventSource ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of HierarchicalReferences.

The semantic of this ReferenceType is to relate event sources in a hierarchical, non-looping organization. This ReferenceType and any subtypes are intended to be used for discovery of Event generation in a Server. They are not required to be present for a Server to generate an Event from its source (causing the Event) to its notifying Nodes. In particular, the root notifier of a Server, the Server Object defined in OPC 10000-5, is always capable of supplying all Events from a Server and as such has implied HasEventSource References to every event source in a Server.

The SourceNode of this ReferenceType shall be an Object that is a source of event subscriptions. A source of event subscriptions is an Object that has its “SubscribeToEvents” bit set within the EventNotifier Attribute.

The TargetNode of this ReferenceType can be a Node of any NodeClass that can generate event notifications via a subscription to the reference source.

Starting from Node “A” and only following References of the HasEventSource ReferenceType or of its subtypes it shall never be possible to return to “A”. But it is permitted that, following the References, there may be more than one path leading to another Node “B”.

7.18    HasNotifier

The HasNotifier ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of HasEventSource.

The semantic of this ReferenceType is to relate Object Nodes that are notifiers with other notifier Object Nodes. The ReferenceType is used to establish a hierarchical organization of event notifying Objects. It is a subtype of the HasEventSource ReferenceType defined in 7.16.

The SourceNode of this ReferenceType shall be Objects or Views that are a source of event subscriptions. The TargetNode of this ReferenceType shall be Objects that are a source of event subscriptions. A source of event subscriptions is an Object that has its “SubscribeToEvents” bit set within the EventNotifier Attribute.

If the TargetNode of a Reference of this type generates an Event, then this Event shall also be provided in the SourceNode of the Reference.

An example of a possible organization of Event References is represented in Figure 27. In this example an unfiltered Event subscription directed to the “Pump” Object will provide the Event sources “Start” and “Stop” to the subscriber. An unfiltered Event subscription directed to the “Area 1” Object will provide Event sources from “Machine B”, “Tank A” and all notifier sources below “Tank A”.

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Figure 27 – Event Reference Example

A second example of a more complex organization of Event References is represented in Figure 28. In this example, explicit References are included from the Server’s Server Object, which is a source of all Server Events. A second Event organization has been introduced to collect the Events related to “Tank Farm 1”. An unfiltered Event subscription directed to the “Tank Farm 1” Object will provide Event sources from “Tank B”, “Tank A” and all notifier sources below “Tank B” and “Tank A”.

Figure32_

Figure 28 – Complex Event Reference Example

8    Standard DataTypes

8.1    General

The remainder of 8 defines DataTypes. Their representation in the AddressSpace and the DataType hierarchy is specified in OPC 10000-5. Other parts of this series of standards may specify additional DataTypes.

8.2    NodeId