Overview
IEC 62541-19:2025 - OPC Unified Architecture, Part 19: Dictionary Reference defines an OPC UA Information Model that standardizes how OPC UA AddressSpaces reference external data dictionaries (for example IEC Common Data Dictionary (IEC CDD) or ECLASS). The standard specifies ObjectTypes, VariableTypes and a ReferenceType to represent dictionary entries and to link OPC UA Nodes to external semantic identifiers (IRDI or URI-based). It enables consistent, machine-readable references from OPC UA models to external classification systems for improved semantic interoperability in industrial automation and IIoT.
Key topics and technical requirements
- Dictionary reference Information Model: Defines the base infrastructure an OPC UA Information Model uses to reference external dictionaries.
- ObjectTypes:
- DictionaryEntryType (abstract) - minimum identification for a dictionary entry.
- IrdiDictionaryEntryType - supports IRDI identifiers conformant with ISO/IEC 11179-6 and ISO 29002-5.
- UriDictionaryEntryType - supports URI-based dictionary entries.
- DictionaryFolderType and a Dictionaries Object - optional hierarchy and foldering for exposing dictionary content.
- ReferenceType:
- HasDictionaryEntry - standardized reference for linking OPC UA Nodes to dictionary entries.
- VariableTypes:
- Multi-state variable types for representing enumerated dictionary-based values (e.g., MultiStateDictionaryEntryDiscreteType).
- Conformance guidance:
- Types are defined for reuse and may be subtyped. Use of these types by servers is strongly recommended (not mandatory).
- Servers may optionally expose dictionary hierarchies; resource constraints (e.g., firmware in field devices) should be considered.
- Normative links: Relies on other OPC UA parts (IEC 62541-1, -3, -5, -8) and metadata standards like ISO/IEC 11179-6.
Applications and who should use it
- Device vendors and firmware developers who want devices to reference standardized semantic dictionaries (IEC CDD, ECLASS).
- OPC UA server and information model designers seeking robust, interoperable semantic linking of nodes.
- System integrators and asset managers who need automated classification, discovery, and validation of device types and properties across systems.
- IIoT and Industry 4.0 solution architects aiming to enhance data semantics for analytics, digital twins, and cross-vendor interoperability.
Practical benefits include automated identification of device types and properties, consistent semantic enrichment, easier integration between engineering tools and runtime systems, and improved data harmonization across enterprise and field levels.
Related standards
- IEC 62541 series (OPC UA): Parts 1, 3, 5, 8 (informative for address space, information model, data access)
- ISO/IEC 11179-6 (IRDI / metadata registries)
- ISO 29002-5 (identification scheme)
Keywords: OPC UA, IEC 62541-19, Dictionary Reference, Information Model, IEC CDD, ECLASS, IRDI, ISO/IEC 11179-6, semantic interoperability, HasDictionaryEntry, DictionaryEntryType, industrial automation, IIoT.
