The first OPC Unified Architecture Book, written by Wolfgang Mahnke, Stefan-Helmut Leitner and Matthias Damm one of the co-founders of ascolab.

OPC UA Specifications

The OPC UA Specification is a multi-part specification and consists of the following parts:

  1. Core Specifications
  2. Access Type Specifications
  3. Utility Type Specifications


In particular, there are the following parts:

  1. Concepts
  2. Security Model
  3. Address Space Model
  4. Services
  5. Information Model
  6. Service Mappings
  7. Profiles
  8. Data Access
  9. Alarms and Conditions
  10. Programs
  11. Historical Access
  12. Discovery
  13. Aggregates

In contrast to the COM based specifications, which were mostly released as API reference, the UA specifications are not pure application specs. They describe mainly UA internal mechanisms which are handled through the communication stack and are only of interest for those who port the stack to a specific target platform or those who want to implement their own UA stack.

The application developer will use the OPC UA stack available in his or her preferred programming language. Apart from language specific differences, the APIs for calling services are identical. Thus, parts 3, 4, and 5 may be most interesting for the application developer.