hiho,
Well, there is the issue of which is concrete and which is abstract. And
then there is the issue of which one points to which as participants in this
relationship.
So first off, in an extend relationship the arrow goes from "an extenion use
case to a base use case specifying how the behavior defined for the
extension use case can be inserted into the behavior defined for the base
use case" [The Unified Modeling Language Reference Manual by Rumbaugh et al,
p272]. The arrow goes from the use case with the extra behavior to the base
use case.
The use case with the extra behavior should be abstract. The extension use
case depends upon the base one and is expetected to exist within the context
of the base one already running. At some extension point, based on some
condition, the extension use case behavior will occur. But it is just a
snippet of behavior, not a concrete use case.
The base use case should be concrete. It should represent a perfectly good
use case that just does not bother to explain any special behavior that
occurs at the extension point when the condition is true.
If one was tempted to have a base use case that is abstract and actually
cannot be considered complete without having the extension, then the
generalization relationship would be more appropriate.
So, in summary, the arrow goes from an abstract use case with the snippet of
extra behavior to the concrete base use case.
-------- b
--
Brian G. Lyons
Number Six Software - Voted Rational's Best Complementary Service Provider
1655 North Fort Myer Drive, Suite 1100
Arlington, VA 22209-3196
http://www.numbersix.com
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Jeroen JANSSENS
Sent: Monday, April 09, 2001 7:33 AM
To: [EMAIL PROTECTED]
Subject: (ROSE) extends relationship question
Hi,
I've read two books about UML recently. The first one states that when you
have an extends
relationship between two use cases, the relationship arrow is drawn from the
concrete use
case to the abstract use case. The other book states the opposite. In Rose,
the two are
possible. Could someone please explain extends relationships some more and
how to model it
correctly in Rose?
Thanks
Jeroen Jansssens
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