Objects of the class can be used to define the resources used by background
activities and by wait actions in a process. The definition of resources for
this activities has the advantage, that all activities using the same resource
are pooled in a separate thread pool in the AT service.
As a special case if a wait action using a resource blocks the
execution of a process (maybe because the resource is not available) all
background activities, that share this resource are blocked also (not only the
activities in the process of the wait action).