3.4 Conventions used in this document
3.4.1 Conventions for Node descriptions
Node definitions are specified using tables (see Table 2 ).
Attributes are defined by providing the Attribute name and a value, or a description of the value.
References are defined by providing the ReferenceType name, the BrowseName of the TargetNode and its NodeClass.
If the TargetNode is a component of the Node being defined in the table the Attributes of the composed Node are defined in the same row of the table.
The DataType is only specified for Variables; “[<number>]” indicates a single-dimensional array, for multi-dimensional arrays the expression is repeated for each dimension (e.g. [2][3] for a two-dimensional array). For all arrays the ArrayDimensions is set as identified by <number> values. If no <number> is set, the corresponding dimension is set to 0, indicating an unknown size. If no number is provided at all the ArrayDimensions can be omitted. If no brackets are provided, it identifies a scalar DataType and the ValueRank is set to the corresponding value (see OPC 10000-3). In addition, ArrayDimensions is set to null or is omitted. If it can be Any or ScalarOrOneDimension, the value is put into “{<value>}”, so either “{Any}” or “{ScalarOrOneDimension}” and the ValueRank is set to the corresponding value (see OPC 10000-3) and the ArrayDimensions is set to null or is omitted. Examples are given in Table 1 .
| Notation | DataType | ValueRank | ArrayDimensions | Description |
| 0:Int32 | 0:Int32 | -1 | omitted or null | A scalar Int32. |
| 0:Int32[] | 0:Int32 | 1 | omitted or {0} | Single-dimensional array of Int32 with an unknown size. |
| 0:Int32[][] | 0:Int32 | 2 | omitted or {0,0} | Two-dimensional array of Int32 with unknown sizes for both dimensions. |
| 0:Int32[3][] | 0:Int32 | 2 | {3,0} | Two-dimensional array of Int32 with a size of 3 for the first dimension and an unknown size for the second dimension. |
| 0:Int32[5][3] | 0:Int32 | 2 | {5,3} | Two-dimensional array of Int32 with a size of 5 for the first dimension and a size of 3 for the second dimension. |
| 0:Int32{Any} | 0:Int32 | -2 | omitted or null | An Int32 where it is unknown if it is scalar or array with any number of dimensions. |
| 0:Int32{ScalarOrOneDimension} | 0:Int32 | -3 | omitted or null | An Int32 where it is either a single-dimensional array or a scalar. |
The TypeDefinition is specified for Objects and Variables.
The TypeDefinition column specifies a symbolic name for a NodeId, i.e. the specified Node points with a HasTypeDefinition Reference to the corresponding Node.
The ModellingRule of the referenced component is provided by specifying the symbolic name of the rule in the ModellingRule column. In the AddressSpace, the Node shall use a HasModellingRule Reference to point to the corresponding ModellingRule Object.
If the NodeId of a DataType is provided, the symbolic name of the Node representing the DataType shall be used.
Note that if a symbolic name of a different namespace is used, it is prefixed by the NamespaceIndex (see 3.4.2.2).
Nodes of all other NodeClasses cannot be defined in the same table; therefore only the used ReferenceType, their NodeClass and their BrowseName are specified. A reference to another part of this document points to their definition.
Table 2 illustrates the table. If no components are provided, the DataType, TypeDefinition and ModellingRule columns may be omitted and only a Comment column is introduced to point to the Node definition.
| Attribute | Value | ||||
| Attribute name | Attribute value. If it is an optional Attribute that is not set “--“ will be used. | ||||
| References | NodeClass | BrowseName | DataType | TypeDefinition | Other |
| ReferenceType name | NodeClass of the TargetNode. | BrowseName of the target Node | DataType of the referenced Node, only applicable for Variables. | TypeDefinition of the referenced Node, only applicable for Variables and Objects. | Additional characteristics of the TargetNode such as the ModellingRule or AccessLevel. |
| NOTE Notes referencing footnotes of the table content. | |||||
Components of Nodes can be complex that is containing components by themselves. The TypeDefinition, NodeClass and DataType can be derived from the type definitions, and the symbolic name can be created as defined in 3.4.3.1. Therefore, those containing components are not explicitly specified; they are implicitly specified by the type definitions.
The Other column defines additional characteristics of the Node. Examples of characteristics that can appear in this column are show in Table 3.
| Name | Short Name | Description |
| 0:Mandatory | M | The Node has the Mandatory ModellingRule. |
| 0:Optional | O | The Node has the Optional ModellingRule. |
| 0:MandatoryPlaceholder | MP | The Node has the MandatoryPlaceholder ModellingRule. |
| 0:OptionalPlaceholder | OP | The Node has the OptionalPlaceholder ModellingRule. |
| ReadOnly | RO | The Node AccessLevel has the CurrentRead bit set but not the CurrentWrite bit. |
| ReadWrite | RW | The Node AccessLevel has the CurrentRead and CurrentWrite bits set. |
| WriteOnly | WO | The Node AccessLevel has the CurrentWrite bit set but not the CurrentRead bit. |
If multiple characteristics are defined they are separated by commas. The name or the short name may be used.
3.4.2 NodeIds and BrowseNames
3.4.2.1 NodeIds
The NodeIds of all Nodes described in this standard are only symbolic names. Annex A defines the actual NodeIds.
The symbolic name of each Node defined in this document is its BrowseName, or, when it is part of another Node, the BrowseName of the other Node, a “.”, and the BrowseName of itself. In this case “part of” means that the whole has a HasProperty or HasComponent Reference to its part. Since all Nodes not being part of another Node have a unique name in this document, the symbolic name is unique.
The NamespaceUri for all NodeIds defined in this document is defined in Annex A. The NamespaceIndex for this NamespaceUri is vendor-specific and depends on the position of the NamespaceUri in the server namespace table.
Note that this document not only defines concrete Nodes, but also requires that some Nodes shall be generated, for example one for each Session running on the Server. The NodeIds of those Nodes are Server-specific, including the namespace. But the NamespaceIndex of those Nodes cannot be the NamespaceIndex used for the Nodes defined in this document, because they are not defined by this document but generated by the Server.
3.4.2.2 BrowseNames
The text part of the BrowseNames for all Nodes defined in this document is specified in the tables defining the Nodes. The NamespaceUri for all BrowseNames defined in this document is defined in Annex A.
If the BrowseName is not defined by this document, a namespace index prefix is added to the BrowseName (e.g., prefix '0' leading to ‘0:EngineeringUnits’ or prefix '2' leading to ‘2:DeviceRevision’). This is typically necessary if a Property of another specification is overwritten or used in the OPC UA types defined in this document. Table 36 provides a list of namespaces and their indexes as used in this document.
3.4.3 Common Attributes
3.4.3.1 General
The Attributes of Nodes, their DataTypes and descriptions are defined in OPC 10000-3. Attributes not marked as optional are mandatory and shall be provided by a Server. The following tables define if the Attribute value is defined by this specification or if it is server-specific.
For all Nodes specified in this specification, the Attributes named in Table 4 shall be set as specified in the table.
| Attribute | Value |
| DisplayName | The DisplayName is a LocalizedText. Each server shall provide the DisplayName identical to the BrowseName of the Node for the LocaleId “en”. Whether the server provides translated names for other LocaleIds is server-specific. |
| Description | Optionally a server-specific description is provided. |
| NodeClass | Shall reflect the NodeClass of the Node. |
| NodeId | The NodeId is described by BrowseNames as defined in 3.4.2.1. |
| WriteMask | Optionally the WriteMask Attribute can be provided. If the WriteMask Attribute is provided, it shall set all non-server-specific Attributes to not writable. For example, the Description Attribute may be set to writable since a Server may provide a server-specific description for the Node. The NodeId shall not be writable, because it is defined for each Node in this specification. |
| UserWriteMask | Optionally the UserWriteMask Attribute can be provided. The same rules as for the WriteMask Attribute apply. |
| RolePermissions | Optionally server-specific role permissions can be provided. |
| UserRolePermissions | Optionally the role permissions of the current Session can be provided. The value is server-specifc and depend on the RolePermissions Attribute (if provided) and the current Session. |
| AccessRestrictions | Optionally server-specific access restrictions can be provided. |
3.4.3.2 Objects
For all Objects specified in this specification, the Attributes named in Table 5 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.
| Attribute | Value |
| EventNotifier | Whether the Node can be used to subscribe to Events or not is server-specific. |
3.4.3.3 Variables
For all Variables specified in this specification, the Attributes named in Table 6 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.
| Attribute | Value |
| MinimumSamplingInterval | Optionally, a server-specific minimum sampling interval is provided. |
| AccessLevel | The access level for Variables used for type definitions is server-specific, for all other Variables defined in this specification, the access level shall allow reading; other settings are server-specific. |
| UserAccessLevel | The value for the UserAccessLevel Attribute is server-specific. It is assumed that all Variables can be accessed by at least one user. |
| Value | For Variables used as InstanceDeclarations, the value is server-specific; otherwise it shall represent the value described in the text. |
| ArrayDimensions | If the ValueRank does not identify an array of a specific dimension (i.e. ValueRank <= 0) the ArrayDimensions can either be set to null or the Attribute is missing. This behaviour is server-specific. If the ValueRank specifies an array of a specific dimension (i.e. ValueRank > 0) then the ArrayDimensions Attribute shall be specified in the table defining the Variable. |
| Historizing | The value for the Historizing Attribute is server-specific. |
| AccessLevelEx | If the AccessLevelEx Attribute is provided, it shall have the bits 8, 9, and 10 set to 0, meaning that read and write operations on an individual Variable are atomic, and arrays can be partly written. |
3.4.3.4 VariableTypes
For all VariableTypes specified in this specification, the Attributes named in Table 7 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.
| Attributes | Value |
| Value | Optionally a server-specific default value can be provided. |
| ArrayDimensions | If the ValueRank does not identify an array of a specific dimension (i.e. ValueRank <= 0) the ArrayDimensions can either be set to null or the Attribute is missing. This behaviour is server-specific. If the ValueRank specifies an array of a specific dimension (i.e. ValueRank > 0) then the ArrayDimensions Attribute shall be specified in the table defining the VariableType. |
3.4.3.5 Methods
For all Methods specified in this specification, the Attributes named in Table 8 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.
| Attributes | Value |
| Executable | All Methods defined in this specification shall be executable (Executable Attribute set to “True”), unless it is defined differently in the Method definition. |
| UserExecutable | The value of the UserExecutable Attribute is server-specific. It is assumed that all Methods can be executed by at least one user. |