OPC UA Specification
OPC 10000-19
OPC Unified Architecture Part 19: Dictionary Reference     Release 1.05.03 2023-12-31

 

 

 

 

 

 

 

CONTENTS

Page

 

1       Scope. 1

2       Normative references 1

3       Terms, definitions, abbreviated terms, and conventions. 1

3.1         Terms and definitions. 1

4       Dictionary Reference Information Model overview. 2

4.1         General 2

4.2         Overview. 2

5       OPC UA ObjectTypes 3

5.1         DictionaryEntryType. 3

5.2         DictionaryFolderType. 4

5.3         IRDI ISO/IEC 11179-6 conformant DictionaryEntryType. 4

5.4         URI based dictionary entry type. 5

6       OPC UA ReferenceTypes 5

6.1         HasDictionaryEntry ReferenceType. 5

7       OPC UA VariableTypes. 6

7.1         MultiStateDictionaryEntryDiscreteBaseType VariableType. 6

7.2         MultiStateDictionaryEntryDiscreteType VariableType. 7

8       OPC UA Objects 7

8.1         Dictionaries Object 7

9       Examples (Informative) 7

 

 

Figures

 

Figure 1 – The dictionary reference types................................................................. 3

Figure 2 – IRDI overview....................................................................................... 4

Figure 3 – DeviceType Property example.................................................................. 7

Figure 4 – Example with references to classes and properties........................................ 8

Figure 5 – Example with two dictionaries.................................................................. 9

 

Tables

Table 1 – DictionaryEntryType definition. 3

Table 2 – DictionaryFolderType definition. 4

Table 3 – IrdiDictionaryEntryType Definition. 5

Table 4 – UriDictionaryEntryType Definition. 5

Table 5 – HasDictionaryEntry ReferenceType 6

Table 6 – MultiStateDictionaryEntryDiscreteBaseType Definition. 6

Table 7 – MultiStateDictionaryEntryDiscreteType Definition 7

Table 8 – Dictionaries Definition. 7

 

 

OPC Foundation

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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 © 2006-2023, OPC Foundation, Inc.

AGREEMENT OF USE

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HTUhttp://www.opcfoundation.org.

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COMPLIANCE

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GENERAL PROVISIONS

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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/errata.

 

Revision 1.05.03 Highlights

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

 

Mantis ID	Scope	Summary	Resolution
	Clarification	IEC Requested changes	Applied requested changes
8543	Clarification	eCl@sss is now ECLASS	Changed name throughout.

 

OPC Unified Architecture Specification

 

Part 19: Dictionary Reference

 

 

 

 

1     Scope

This specification defines an Information Model of the OPC Unified Architecture. The Information Model describes the basic infrastructure to reference from an OPC UA Information Model to external dictionaries like IEC Common Data Dictionary or ECLASS.

2     Normative references

The following referenced documents are indispensable for the application of this specification. 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 10000-3, OPC Unified Architecture - Part 3: Address Space Model

http://www.opcfoundation.org/UA/Part3/

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

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

OPC 10000-100, OPC Unified Architecture - Part 8: Data Access

http://www.opcfoundation.org/UA/Part100/

ISO/IEC 11179-6, Information technology – Metadata registries (MDR) – Part 6: Registration

https://www.iso.org/standard/60342.html

ISO 29002-5, Information automation systems and integration – Exchange of characteristic data – Part 5: Identification scheme

https://www.iso.org/standard/50773.html

ISO/IEC 6523, Information technology – Structure for the identification of organizations and organization parts

https://www.iso.org/standard/25773.html

 

3     Terms, definitions, abbreviated terms, and conventions

3.1      Terms and definitions

For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-3, and OPC 10000-5 apply.

All used terms are italicized in the specification.

4     Dictionary Reference Information Model overview

4.1      General

This document describes the basic infrastructure an OPC UA Information Model may use to reference external dictionaries like IEC Common Data Dictionary or ECLASS. It defines ObjectTypes, VariableTypes and a ReferenceType and explains how they should be used.

The ObjectTypes are used to represent an external dictionary in an OPC UA AddressSpace. The ReferenceType is used to reference from Nodes in the AddressSpace to the dictionary entries. Such dictionary entries can be seen as external classification or external semantic information.

The type system of OPC UA already provides means to express the semantic of an OPC UA Object. As an example, OPC 10000-100 defines the DeviceType ObjectType expressing that instances of this ObjectType represent devices. Subtypes of the DeviceType are used to add vendor specific semantic. However, the classification and additional semantic of the device in terms of an external data dictionary is not specified further. This document provides means to represent that an Object is for example a differential pressure transmitter in the context of an IEC Common Data Dictionary. This allows clients to automatically retrieve and identify such devices.

This document is an integral part of this standard, that is, the types defined in this document shall be used as defined. However, it is not required but strongly recommended that a Server use the types defined in this document to refer to external dictionaries. The defined types may be subtyped to refine their behaviour.

When a Server references external dictionaries using the types defined in this document, it refers from OPC UA Nodes to dictionary entries. The Server may optionally also provide the hierarchy and content of the external dictionary. Resource consumption needs to be considered, especially in scenarios where the OPC UA Server is part of the firmware of a device.

4.2      Overview

The types and instances defined in this document are illustrated in Figure 1. The DictionaryEntryType is an abstract base type for dictionary entries. The IrdiDictionaryEntryType and the UriDictionaryEntryType provide concrete types that can be used to represent dictionary entries. The HasDictionaryEntry ReferenceType is used to refer an OPC UA Node to a dictionary entry. The DictionaryFolderType and the Dictionaries Object provide an optional capability to expose the hierarchy of a referenced dictionary.

Figure 1 – The dictionary reference types

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.

Table 1 – DictionaryEntryType definition

 

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.

Table 2 – DictionaryFolderType definition

 

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.

Figure 2 – IRDI overview

Examples for IRDI strings defined by standards using the IRDI format

IEC CDD            0112/2//a/61360_4#AAE867#001    Proximity switch, Output current

ISO 5598           0112-1-a-18582#KAA802#s           Pneumatic value

ECLASS            0173/1///#02-8AD792#s                 Inductive distance sensor, Design of analog output

Table 3 – IrdiDictionaryEntryType Definition

 

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.

Table 4 – UriDictionaryEntryType Definition

 

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).

6     OPC UA ReferenceTypes

6.1      HasDictionaryEntry ReferenceType

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

The Reference to the dictionary entry for any Node is provided by HasDictionaryEntry.

The SourceNode of this ReferenceType can be any Node. The TargetNode of this ReferenceType shall be an Object of DictionaryEntryType or one of its subtypes.

Each Node can be the SourceNode of multiple HasDictionaryEntry References pointing to multiple dictionary entry Objects.

The HasDictionaryEntry ReferenceType is specified in Table 5.

Table 5 – HasDictionaryEntry ReferenceType

Attributes	Value
BrowseName	HasDictionaryEntry
InverseName	DictionaryEntryOf
Symmetric	False
IsAbstract	False
References	NodeClass	BrowseName	Comment
Subtype of the NonHierarchicalReferences ReferenceType defined in OPC 10000-3
Conformance Units
Address Space Dictionary Entries

 

 

 

 

7     OPC UA VariableTypes

7.1      MultiStateDictionaryEntryDiscreteBaseType VariableType

The MultiStateDictionaryEntryDiscreteBaseType VariableType is a subtype of the MultiStateValueDiscreteType. It provides dictionary entries for each of the possible states as well as the current state of the MultiStateValueDiscreteType. It is formally defined in Table 6.

Table 6 – MultiStateDictionaryEntryDiscreteBaseType Definition

 

The normal approach of associating DictionaryEntryType Nodes with HasDictionaryEntry References cannot be used with a MultiStateValueDiscreteType VariableType due to the EnumValues Property being an Array, making this Type necessary. References can however be used for other VariableTypes. For example, the TwoStateDiscreteType can use HasDictionaryEntry References with SourceNode being the TrueState and FalseState Properties and TargetNode being the DictionaryEntry Nodes.

EnumDictionaryEntries is a two-dimensional array of NodeIds. The first dimension is used to list all possible dictionary entry values for the related variable in a specific dictionary (e.g. CDD or ECLASS). The second dimension is used to reference this dictionary. The size of the first array dimension shall be the same size as the EnumValues Property.

ValueAsDictionaryEntries provides a list of all dictionary entry values in the different dictionaries related to the current value of the variable. The order of the array entries shall be in the same order used by the EnumDictionaryEntries Property.

If an instance of this type is writeable and the optional ValueAsDictionaryEntries Property is implemented, it shall be writeable as well. Clients writing to the ValueAsDictionaryEntries Property shall use one of the DictionaryEntryType NodeIds defined by the EnumDictionaryEntries Property. This will have the same result as writing the value attribute, but the client does not require knowledge of the values.

The NodeIds represent the dictionary entries and can be generated with dictionary knowledge.

7.2      MultiStateDictionaryEntryDiscreteType VariableType

The MultiStateDictionaryEntryDiscreteType VariableType is a subtype of the MultiStateDictionaryEntryDiscreteBaseType. It requires the ValueAsDictionaryEntries Property. It is formally defined in Table 7.

Table 7 – MultiStateDictionaryEntryDiscreteType Definition

 

8     OPC UA Objects

8.1      Dictionaries Object

The Dictionaries Object is used as the browse entry point for dictionaries referenced in the Server. The Object is optional and can be used to expose the hierarchy of the referenced dictionaries or dictionary entries referenced by other Nodes.

The Dictionaries Object is a component of the Server Object defined in OPC 10000-5. The Dictionaries Object references DictionaryEntryType and DictionaryFolderType Object Nodes. It is formally defined in Table 8.

Table 8 – Dictionaries Definition

 

9     Examples (Informative)

The example in Figure 3 shows how OPC UA Properties of the DeviceType defined in OPC 10000-100 refer dictionary entries in the IEC 61987 Common Data Dictionary.

Figure 3 – DeviceType Property example

The example in Figure 4 shows how OPC UA Objects could refer to classes in the IEC 61987 Common Data Dictionary and OPC UA Properties to properties in the data dictionary.

In this example, the weight property is referenced from two OPC UA Properties and the different semantic is provided by the referenced classes Transmitter housing or Transmitter body of the parent OPC UA Objects.

Figure 4 – Example with references to classes and properties

The example in Figure 5 shows how a server can expose the hierarchy of two dictionaries below the optional Dictionaries Object.

Figure 5 – Example with two dictionaries

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