5 Fundamentals

5.1 Meta-model Mapping Approach

5.1.1 General

ISA-95 defines the meta-models to describe object models using UML notation (See Annex E). This standard defines mapping between the UML notation and the OPC UA meta-model to transform the object model defined in ISA-95 into an OPC UA Address Space Model. (See OPC 10000-3, 0, OPC UA Meta Model)

5.1.2 ISA95Class

ISA95Class is a concept to represent a classification of ISA95 Resource and is represented by a UML Class and an OPC UA ObjectType (see Table 2).

5.1.3 ISA95Object

ISA95Object is a concept to represent resources like a Role Base Equipment and is represented by a UML Class and an OPC UA ObjectType and OPC UA Objects (see Table 3).

5.1.4 ISA95Attribute

ISA95Attribute is a minimum set of industry-independent information and is described in the attribute table defined in ISA-95. ISA-95 doesn’t describe an attribute in UML. In OPC UA it can be represented by Attributes, VariableTypes, Variables, and Properties (see Table 4),

5.1.5 ISA95Property

ISA95Property is a concept to represent characteristics for domain specific information. Accordingly ISA-95 defines that attributes that are application or industry specific are to be modelled in terms of properties and represented in property classes in the model. ISA-95 doesn’t describe a property as an attribute in UML, but describes a property as a Class. In OPC UA it can be represented by VariableTypes and Variables (see Table 5)

5.1.6 Complex Value

5.1.6.1 General

OPC UA allows information to be represented as complex Variables (Variable with nested sub-variable) and/or as complex DataTypes, where a DataType has a structure or other special meaning associated with it. Each of the nested Variables can have a value that represents a simple base DataType such as an Integer or can represent a custom DataType such as a Currency or a structure.

The format of a value is represented by Attributes of Variables. This standard maps all value formats defined in ISA-95 into those attributes.

5.1.6.2 Array value

Arrays of values are represented by DataType, ValueRank, ArrayDimensions, and MaxArrayLength attribute of a VariableType. (See OPC 10000-3). The following examples illustrate the usage of these Attributes:

1. A set of values for a single dimension array of integers with 6 values

2. EBNF: [ 1 , 2 , 3 , 4 , 5 , 6]

3. OPC UA: DataType=Int32(any), ValueRank=OneDimension(1), ArrayDimensions=6, MaxArrayLength=6.

4. A set of values for a two dimension array of size 2x3

5. EBNF: [ [1 , 2] , [3 , 4] ,[5 , 6]]

6. OPC UA: DataType=Int32(any), ValueRank= 2, ArrayDimensions=[2,3], MaxArrayLength=6

7. A set of values for a four dimension array of size 2x3x4x5

8. EBNF: omitted for simplicity

9. OPC UA: DataType=Int32(any), ValueRank= 4, ArrayDimensions=[2,3,4,5], MaxArrayLength=120

5.1.6.3 Range value

Ranges of values are represented by Range DataType defined in OPC 10000-8. If the Range is an array, then ValueRank, ArrayDimensions, and MaxArrayLength attributes are utilized to indicate an array.

1. A simple range of values

2. EBNF: {0..100}

3. OPC UA : DataType=Range, ValueRank= Scalar (−1)

4. A non-continuous range of values

5. EBNF: {0 .. 100 , 200 .. 300 , 500 , 600 .. 650}

6. OPC UA : DataType=Range, ValueRank= OneDimension (1), ArrayDimensions=4

5.1.6.4 Series value

A set of allowed values is defined in EnumStrings and the EnumValues Standard Property of Enumeration DataType.

1. A series of values that defines colours.

2. EBNF: <Red, Green, Yellow, Blue>

3. OPC UA : Array of LocalizedText that is a list of the enumeration strings is set to EnumStrings

5.1.6.5 Structured value

Structured data element is defined in custom DataType derived from Structure DataType or is represented by nested VariableType that has Variables as children.

1. A structured data element represented as flattened Property Name

2. Struct Simple {

3. Integer Position;

4. Float LastValue;

5. Boolean Exists;

6. String Comment;}

7. ISA-95: Simple.Position, Simple.LastValue, Simple.Exists, Simple.Comment

1. A structured data element represented by creating an ISA95Property with no data value with nested child ISA95Properties and identification of element.

2. Struct Simple {

3. public int Position;

4. public double LastValue;

5. public bool Exists;

6. public string Comment;}

7. ISA-95: Property [ID=”Simple”]

8. Property [ID=”Simple”]\ Property [ID=”Position”]

9. Property [ID=”Simple”]\ Property [ID=”LastValue”]

10. Property [ID=”Simple”]\ Property [ID=”Exists”]

11. Property [ID=”Simple”]\ Property [ID=”Comment”]

A combination of a) and b) where a structured data element represented by creating a ISA95 Property with a data value that is a structured data element and with nested child properties and identification of element (see Figure 14). This is the preferred method for modelling complex information. [Note: the figure flow the template defined in OPC 10000-3 with some extensions defined in Annex F]

5.1.7 ISA95Reference

5.1.7.1 General

ISA95Reference is a concept that represents a relationship between modelling targets and is represented by UML Association and by OPC UA ReferenceType (see Table 6).

5.1.7.2 UMLAssociation

UMLAssociation represents an association between elements of a class and elements of another or the same class. The UMLAssociation is transformed to subtypes of OPC UA NonHierarchicalReferences (see Table 7).

Instance Nodes that are referenced by NonHierarchicalReferences are not instantiated when an instance of an ObjectType or VariableType is created.

5.1.7.3 UMLGeneralization

UMLGeneralization is used to describe that an element of UMLClass is a specialized type of the super UML Class, it mapped to the OPC UA HasSubtype ReferenceType.

5.1.7.4 UMLDependence

UMLDependence is a weak association that is used to describe a modelling element that depends on another modelling element. This standard doesn’t support this concept in general terms. Depending on the nature of the dependence it may be modelled as a custom reference.

5.1.7.5 UMLAggregation

UMLAggregation is used to describe that an element of the class is made up of elements of other classes; it is mapped to subtypes of the OPC UA Aggregates ReferenceType (see Table 8).

5.1.7.6 UMLComposite

UMLComposite is used to describe a strong form of aggregation, it is mapped to OPC UA HasComponent or subtypes of OPC UA HasComponent ReferenceType (see Table 9).

5.2 Model Overview

Figure 15 illustrates an overview of ISA-95 OPC UA Information Model. This overview is not complete, additional figures in later section will provide additional details of the information model. ISA-95 Base Information Model defines all models that are commonly utilized in this standard. This model includes a data representation model that is based on UN/CEFACT Core Data Type (CDT) (see UN/ECE). ISA-95 Common Object Model defines the models that represent all ISA95Resources and relationship between them.