5 OPC UA ObjectTypes

5.1 DictionaryEntryType

This abstract ObjectType defines the minimum information needed to identify the data dictionary entry for a respective standard (e.g. IEC Common Data Dictionary). It is formally defined in Table 1.

Concrete dictionary entry types shall inherit from the abstract DictionaryEntryType defining additional Properties and Objects as necessary and specified by the standard body (e.g. further definitions, versioning information etc.).

An instance of such a concrete dictionary entry ObjectType represents an entry in an external data dictionary.

Instances of the DictionaryEntryType can be nested in order to create hierarchies of dictionary entries

5.2 DictionaryFolderType

This ObjectType provides means to structure dictionary entry Objects. Multiple Objects of the DictionaryFolderType can be nested in order to create hierarchies. The DictionaryFolderType is formally defined in Table 2.

5.3 IRDI ISO/IEC 11179-6 conformant DictionaryEntryType

The IrdiDictionaryEntryType defined in Table 3 is used to represent dictionary entries that use standardized semantic identifiers that conform with International Registration Data Identifiers (IRDI) defined in ISO/IEC 11179-6.

Standardized semantic identifiers are locale independent strings typically specified in international standards like IEC CDD (Common Data Dictionary) (IEC 61987). In order to avoid conflict with various name spaces in these identifiers, the registration authority identifier part of the string used shall be based on ISO 29002-5.

Figure 2 shows the general structure and syntax defined by ISO/IEC 11179-6, ISO 29002-5 and ISO/IEC 6523.

Examples for IRDI strings defined by standards using the IRDI format

The identifier in the respective external dictionary shall be a unique string. This identifier is used for the NodeId and the BrowseName Attributes of instances of the DictionaryEntryType. The IdentifierType of the NodeId shall be STRING_1 with the identifier from the external dictionary as the value.

The namespace “http://opcfoundation.org/UA/Dictionary/IRDI” shall be used for instance of the IrdiDictionaryEntryType. Subtypes may define different namespaces.

The identifier shall be immutable; meaning that it shall not be reassigned to a different dictionary entry within the scope of the namespace in future versions. Data dictionaries may be publicly defined by standard bodies such as IEC or proprietary (e.g. vendor-specific dictionaries).

5.4 URI based dictionary entry type

The UriDictionaryEntryType defined in Table 4 is used to represent dictionary entries that use URIs as unique identifiers.

The identifier in the respective external dictionary shall be a unique URI string. This identifier is used for the NodeId and the BrowseName Attributes of instances of the DictionaryEntryType. The IdentifierType of the NodeId shall be STRING_1 with the identifier from the external dictionary as the value.

The namespace “http://opcfoundation.org/UA/Dictionary/URI” shall be used for instance of the UriDictionaryEntryType. Subtypes may define different namespaces.

The identifier shall be immutable; meaning that it shall not be reassigned to a different dictionary entry within the scope of the namespace in future versions. Data dictionaries may be publicly defined by standard bodies such as IEC or proprietary (e.g. vendor-specific dictionaries).