This specification defines the OPC Unified Architecture (OPC UA) Services. The Services described are the collection of abstract Remote Procedure Calls (RPC) that are implemented by OPC UA Servers and called by OPC UA Clients. All interactions between OPC UA Clients and Servers occur via these Services. The defined Services are considered abstract because no particular RPC mechanism for implementation is defined in this part. OPC 10000-6 specifies one or more concrete mappings supported for implementation. For example, one mapping in OPC 10000-6 is to XML Web Services. In that case the Services described in this part appear as the Web service methods in the WSDL contract.
Not all OPC UA Servers will need to implement all of the defined Services. OPC 10000-7 defines the Profiles that dictate which Services need to be implemented in order to be compliant with a particular Profile.