Definition of use case and scenario

Please remind me if we have discussed this before.  If not, I propose the
following text for the usage document:

In the context of Web services, a use case is a sequence of interactions
between a service requestor and one or more services, which achieve
measurable results for the requestor. Highlighting either architectural or
technical significance, a usage scenario represents an atomic step in a path
through a use case. By combining and adopting different usage scenarios, one
can thus produce different paths for the same use case. 


Hao