Glossary · Semantic interoperability and information models
OPC UA companion specification
Also known as: Companion specification, OPC UA information model
German: OPC-UA-Companion-Spezifikation
In OPC UA, a companion specification is a standardized information model for a particular domain, device type or industry, developed by the OPC Foundation, often jointly with other organizations such as VDMA, that defines object types, variables and methods on top of the OPC UA base model. Examples are OPC UA for Machinery and OPC UA for Robotics.
- Information models
- Standards
In one sentence
An OPC UA companion specification is a standardized information model for a domain or device type built on the OPC UA base model.
Example
Because both injection molding machines implement the same companion specification, the MES reads their cycle data with one configuration instead of two.
How it applies
- Engineering: Implementing a companion specification means exposing data in the defined structure and with the defined names and types. Check which parts are mandatory and which are optional.
- Integration: Companion specifications give semantic interoperability between devices from different vendors. They are distributed as OPC UA NodeSet files that tools can import.
- Documentation: State exactly which companion specifications and versions a product supports, including optional parts and vendor-specific extensions. Vague claims such as OPC UA compatible are not enough for integrators.
Protocol vs. data model
OPC UA as such provides the communication and the base modeling concepts. A companion specification provides the domain data model. Two OPC UA devices can communicate perfectly and still expose incompatible data if they do not share a companion specification.