views:

277

answers:

3

if A is extension use case (not base use case), can A be directly referenced by the actor?

A: 

You can make the case that there are two kinds of use cases:

  • Abstract -- not directly experience by an actor, but extensions ("subclasses") are.

  • Concrete -- experienced by an actor.

S.Lott
in use-case terminology, I don't think extensions are like subclasses, they're more like 'alternate paths'
Steven A. Lowe
@Steven A. Lowe: the "alternate" is roughly analogous to a subclass which overrides selected steps. Use Cases are defined as being object-oriented by Jacobson. They're not literally classes, but there are intentional parallels.
S.Lott
@[S.Lott]: use-cases have a Generalization relationship, different from Extends (see http://publib.boulder.ibm.com/infocenter/rsmhelp/v7r0m0/index.jsp?topic=/com.ibm.xtools.modeler.doc/topics/cextend.html) - but i think i agree with your analogy, extension points are like overridden methods...
Steven A. Lowe
Extension points are really like conditionally inserted methods, rather than overridden methods.
Doug Knesek
A: 

yes; the fact that A extends some other use-case does not 'hide' it from actors

Steven A. Lowe
+1  A: 

YES The user can as said above, but does not indirectly reference/use it, it must be explicitly modeled.

Drive Truck extends Drive Steering Based Vehicle. It make sense that the Actor could reference either.

Ted Johnson