6 Systems concepts

6.3 OPC UA Servers

6.3.6 OPC UA Service Interface

6.3.6.1 General 
The Services defined for OPC UA are described in Clause 6.4, and specified in OPC 10000-4.
6.3.6.2 Request/response Services 
Request/response Services are Services invoked by the Client through the OPC UA Service Interface to perform a specific task on one or more Nodes in the AddressSpace and to return a response.
6.3.6.3 Subscription Services 
The Publish Service is invoked through the OPC UA Service Interface for the purpose of periodically sending Notifications to Clients. Notifications include Events, Alarms, data changes and Program outputs.