The OPC UA Specification is a multi-part specification and consists of the following parts:
In particular, there are the following parts:
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.