The Base: OPC UA infrastructure
OPC UA has been designed for scalability and supports a wide range of application domains, ranging from field level (e.g. devices for measurement or identification, PLCs), to enterprise management support. To achieve these design goals, the OPC UA standard provides a multi-layered architecture as shown in the following figure:
OPC UA is built on the following Infrastructure:
- Discovery which allows Clients to find OPC UA Servers, their supported protocols, security policies and other capabilities.
- Transport which defines protocol mappings that allow establishing a connection and exchanging well-formed messages between OPC UA Applications.
- Information Access which comprises the means to expose object-based Information Models in an Address Space and the Services to access this information.
- Security and Robustness, which are integrated into Transport and Information Access.
Information models are layered on top of this infrastructure. OPC UA specifies a number of base information models (DataAccess – DA, Alarms&Conditions – AC, and more) that define commonly used objects including both real-time and historical data variables and alarms.
New Information Models can be created based on the OPC UA Data Model and eventually derived from OPC UA Base Information Models. The specifications of such Information Models (“Industry standard models” because they typically address a dedicated industry problem) are called Companion Specifications. The synergy of the OPC UA infrastructure to exchange such industry information models enables interoperability at the semantic level.
A number of companion specifications have already been created.
OPC Foundation differentiate three ways of producing companion specifications:
These are models created by OPC-internal working groups. They can be found here https://opcfoundation.org/developer-tools/specifications-unified-architecture following the core OPC UA parts.
These are models that are created in a joint working group between the OPC Foundation and another organization. These joint specifications represent the majority. The released joint companion specifications can be found here: https://opcfoundation.org/developer-tools/specifications-opc-ua-information-models
The JOINT working group program is defined here: https://opcfoundation.org/joint-working-groups/
Companion specifications can also be created independent of the OPC Foundation.
To support creating companion specifications, the OPC Foundation created a template. It is available for download here: https://opcfoundation.org/developer-tools/specifications-unified-architecture/opc-ua-companion-specification-template/
Furthermore, this list of experts (https://opcfoundation.org/experts/) offer services to vendors or organizations.