IEC 62541-3:2020

Overview - IEC 62541-3:2020 (OPC UA Address Space Model)

IEC 62541-3:2020 defines the OPC Unified Architecture (OPC UA) AddressSpace Model - the meta-model on which OPC UA information models are built. This third edition replaces the 2015 edition and formalizes how nodes, node classes, references, types, variables, methods, events and data types are modeled inside an OPC UA server. The standard is essential for consistent, interoperable OPC UA information modeling used in industrial automation, IIoT and Industry 4.0 solutions.

Key topics and technical changes

• AddressSpace concepts and Node Model: defines NodeClasses (Object, Variable, Method, DataType, ReferenceType, View), attributes, and reference structures used to browse and organize information.
• Type and Instance models: rules for ObjectTypes, VariableTypes, subtyping, instance declarations and instantiation constraints.
• Variables and DataTypes: definitions for Variables, DataVariables, Properties and encodings for complex and built‑in data types.
• Event and Method models: event types, event categorization and modelling of Methods (including OptionalPlaceHolder and MandatoryPlaceHolder usage).
• Security and authorization: introduction of Roles and Permissions to enable role‑based authorization and evaluation of permissions.
• Significant edits in Edition 3:
  • New, improved approach for exposing structure definitions: a DataType Node attribute contains a binary description.
  • New Variable flags to indicate atomicity for read/write operations.
  • Roles and Permissions for role‑based access control.
  • Added data types: Union, Decimal, OptionSet, DateString, TimeString, DurationString, NormalizedString, DecimalString, and AudioDataType.
  • Defined use of ModellingRules OptionalPlaceHolder and MandatoryPlaceHolder for Methods.
  • Optional Properties MaxCharacters and MaxByteStringLength on Variable Nodes.

Applications and practical value

• Use for designing OPC UA information models for: PLCs, DCS, SCADA, sensors, controllers, digital twins and data historians.
• Enables interoperability across vendors by standardizing node, type and data type definitions.
• Guides implementers building OPC UA servers and clients, model authors creating companion specifications, system integrators mapping legacy systems to OPC UA.
• Supports secure, role‑based access control and accurate data encoding for complex IIoT scenarios.

Who should use this standard

• OPC UA implementers (server/client developers)
• Device manufacturers and industrial software vendors
• System integrators and automation architects
• Companion Specification authors and information model designers
• Security and IIoT architects

Related standards

• Other parts of the IEC 62541 (OPC UA) series covering core services, security, encodings and mappings - referenced when implementing full OPC UA stacks and companion specifications.

Keywords: IEC 62541-3:2020, OPC UA AddressSpace, OPC Unified Architecture, Address Space Model, NodeClasses, DataTypes, Roles and Permissions, ModellingRules, industrial automation, IIoT.