Methodsrepresent the function calls of Objects. They are defined in OPC 10000-3. Methodsare invoked and return only after completion (successful or unsuccessful). Execution times for Methodsmay vary, depending on the function that they perform.

The Method Service Setdefines the means to invoke Methods. A Methodshall be acomponentof an Object. Discovery is provided through the Browseand Query Services. Clientsdiscover the Methodssupported by a Serverby browsing for the owning Objects Referencesthat identify their supported Methods.

Because Methodsmay control some aspect of plant operations, Methodinvocation may depend on environmental or other conditions. This may be especially true when attempting to re-invoke a Methodimmediately after it has completed execution. Conditions that are required to invoke the Methodmight not yet have returned to the state that permits the Methodto start again.