Integrated automation facilities manage their operations through the exchange of data and the coordinated invocation of system Functionsas illustrated in Figure 1. Servicesare required to perform the data exchanges and to invoke the Functionsthat constitute system operation. These Functionsmay be invoked through Human Machine Interfaces, cell controllers, or other supervisory control and data acquisition type systems. UA defines Methodsand Programsas an interoperable way to advertise, discover, and request these Functions. They provide a normalizing mechanism for the semantic description, invocation, and result reporting of these Functions. Together Methodsand Programscomplement the other UA Servicesand ObjectTypesto facilitate the operation of an automation environment using a client-server hierarchy.
Methodsand Programsmodel Functionstypically have different scopes, behaviours, lifetimes, and complexities in Serversand the underlying systems. These Functionsare not normally characterized by the reading or writing of data which is accomplished with the UA Attributeservice set.
Methodsrepresent basic Functionsin the Serverthat can be invoked by a Client. Programs, by contrast,model more complex and stateful functionality in the system. For example, a method call may be used to perform a calculation or reset a counter. A Programis used to run and control a batch process, execute a machine tool part program, or manage a domain download. Methodsand their invocation mechanism are described in OPC 10000-3and OPC 10000-4.