The YAWL control center is an indispensable application. It can be used by administrators to perform administrative tasks like loading new specifications, cancelling cases, adding new users etc. It can also be used by ordinary users to process their worklist.
But who starts workflows in practice? Suppose that you are an employee in an enterprise and you want to start the workflow for an application for leave. You would not want to go to the central workflow admin for that. In YAWL you cannot give the right to start workflows selectively to users. Either you cannot start workflows at all or you can start all workflows (because you are admin).
The solution is that the YAWL engine is always running under an application (e. g. a web-portal) that has its own user administration and that can start workflows. Thus you can selectively provide users with "buttons" to start the workflows they need.