Methodsare “lightweight” functions, whose scope is bounded by an owning (see Note) Object, similar to the methods of a class in object-oriented programming or an owning ObjectType, similar to static methods of a class. Methodsare invoked by a client, proceed to completion on the Serverand return the result to the client. The lifetime of the Method’sinvocation instance begins when the client calls the Methodand ends when the result is returned.

NOTE The owning Objector ObjectTypeis specified in the service call when invoking the Method.

While Methodsmay affect the state of the owning Object, they have no explicit state of their own. In this sense, they are stateless. Methodscan have a varying number of input arguments and return resultant arguments. Each Methodis described by a Nodeof the Method NodeClass. This Nodecontains the metadata that identifies the Method’sarguments and describes its behaviour.

Methodsare invoked by using the Call Servicedefined in OPC 10000-4.

Clientsdiscover the Methodssupported by a Serverby browsing for the owning Objects Referencesthat identify their supported Methods.