IEC 62541-8:2020

Overview

IEC 62541-8:2020 is Part 8 of the OPC Unified Architecture (OPC UA) series and defines the information model for Data Access (DA). It specifies the VariableTypes, NodeClass and Attribute descriptions, additional Properties, DataTypes and behavior needed to represent and expose real-time automation data in an OPC UA address space. This third edition (2020) is a technical revision of the 2015 edition and clarifies Data Access semantics and mappings to legacy OPC COM DA.

Key topics and technical requirements

• VariableTypes and DataItems: Defines DataItemType and specialized VariableTypes such as AnalogItem, DiscreteItem, ArrayItem, YArrayItem/XYArrayItem, ImageItem, CubeItem and NDimensionArrayItem for modeling automation signals and multi-dimensional measurements.
• Attributes and AddressSpace usage: Specifies how DataItems are represented in the OPC UA address space and the attributes required to describe value, quality, timestamp and metadata.
• DataTypes and metadata: Includes structured DataTypes such as Range, EUInformation, ComplexNumberType, DoubleComplexNumberType, AxisInformation and XVType to capture engineering units, limits, axes and complex values.
• Quality, status codes and behavior: Defines DA-specific status codes, PercentDeadband handling and operation-level result codes for GOOD/UNCERTAIN/BAD quality conditions. The ambiguous description of Bad_NotConnected was clarified in this edition.
• Interop with OPC COM DA: An informative Annex provides a recommended mapping between OPC UA DataAccess and OPC COM DataAccess, aiding migration and interoperability.
• Standards alignment: EUInformation reference updated to the latest UN/CEFACT units. The full address space model and service semantics remain tied to IEC 62541-3 and IEC 62541-4 respectively.

Applications and practical value

• Modernizing industrial systems: Model sensors, actuators, telemetry and multi-dimensional process data in SCADA, DCS, PLC and IIoT platforms using OPC UA DA VariableTypes.
• Interoperability and migration: Use the COM DA-to-UA mapping to bridge legacy OPC Classic servers/clients to OPC UA without losing DA semantics.
• Software and device development: Implement consistent metadata (units, ranges, axis info) for reliable visualization, alarming, historization and analytics.
• System integration: Ensure standardized representation of engineering units, quality, and timestamps across diverse vendors and tools.

Who should use this standard

• Automation and control system vendors, OPC UA stack and SDK developers
• Device manufacturers and sensor vendors
• System integrators, OT engineers and SCADA architects
• Test laboratories and certification bodies validating OPC UA DA interoperability

Related standards

• IEC 62541-3 - OPC UA: Address space model (complete NodeClasses and Attributes)
• IEC 62541-4 - OPC UA: Services (data access and interaction services)
• Other OPC UA Parts (security, profiles and transport) relevant to implementation and deployment

Keywords: IEC 62541-8, OPC UA, Data Access, AnalogItem, VariableTypes, EUInformation, OPC COM DA mapping, address space, DataItems, industrial automation.