Interface to represent an external application that requires the
workflow execution context in order for it to complete its tasks. The
developer of the application will need to implement the interface and
the engine will deliver the context before the application is called. If
the workflow execution context is not needed by the application, then this
interface is not required. The call made to the application to execute its
tasks does not require a signature defined in this or any other interface,
because the workflow engine can adapt to the native signature of the
application as identified in the workflow process definition. This
interface is provided only as a utility for clients that need information
from the workflow engine in order to execute.