Follow these steps to produce a use case:                   09/22/1996

 - Determine the "boundary" of the system; that is, define which
   objects are part of the system, which ones interact whith it, and
   which ones are disconnected from it. Develop the use case by
   considering the system itself as a single object, a black box.

 - Determine the actors that interface with the system. An actor is
   one role that outside objects play with respect to the
   system. Start by examining physical objects that interact with the
   sytem; in many cases each object plays multiple roles. For example,
   a given person might be a User, an Operator, and an Administrator
   of a computer operating system. Each role represents a different
   actor.

 - For each actor, determine the fundamentally different ways in which
   the actor uses the system. Each of these is a use case. You must be
   able to enumerate the use cases. If you have too many, approach
   things at a higher level.

 - Identify the initial event that starts each use case.

 - Determine the termination condition that concludes the use case.
   Often a use case can be approached at several different levels, so
   pick the level of detail that is compatible with other use cases in
   the system.

 - List a prototypical scenario that describes the transaction.

 - If there are variations, list additional prototypical scenarios or
   decribe these variations in words. Feel free to use ordinary
   language; a use case is not meant to be highly formalized.

 - Identify and describe all the exceptions that are logically
   associated with a given use case.

When you are done, check that the set of use cases encompasses all the
functionality of the system.


Copyright 1995 Rational Software Corporation. Rational Rose -
Application Notes p. 71