6.3.1 General Considerations on handling method processing

In OPC UA, each service call is executed asynchronously between Client and Server. This is also true for calling an OPC UA Method from a Client. However, a Method call is expected to return a result rather fast (milliseconds or seconds, when provided to a UI it should be milliseconds up to small fractions of a second), not after minutes. Therefore, in cases where the actual execution like creating a product may take longer, the Method is returning a result immediately, before the execution has been done, and the status of the execution is provided by some Variables. This is applied in various places in this specification.

In order to not lose any data, Clients should subscribe to the status Variables to get notified about all changes of the status.