...... the lecturer was right the second time !! ummm..... one has to
remember in UML we have what is called as a "weak relationship" - for
example: "Association" is a weak form of Aggregation". When a usecase is
talking to another secondary actor what if an acknowledgement is required !
In such a case a bi-directional flow would be necessary.
.... so ....... Moral of the story:
"If u are'nt sure use weak relationships" - (especially when u are'nt
coding !).......
Hope I have helped in enriching your knowledge.
T.C.Balachandra
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Anna Zee
Sent: Thursday, October 11, 2001 4:32 AM
To: 'Brian G. Lyons'
Cc: '[EMAIL PROTECTED]'
Subject: RE: (ROSE) Use case to actor Yes or No
++++++++++++++++++++++++++++++++++++++++++++++++++
Please read the disclaimer at the bottom of this e-mail.
++++++++++++++++++++++++++++++++++++++++++++++++++
I forgot to say - the lecturer also said that this was not a long-held
convention and not all of the Rational coursework followed it.
-----Original Message-----
From: Brian G. Lyons [mailto:[EMAIL PROTECTED]]
Sent: 10 October 2001 20:31
To: Eric D. Tarkington; Shukla, Susmita (CICG DTAG)
Cc: ROSE_FORUM; Kurt Bittner; Geri Winters
Subject: RE: (ROSE) Use case to actor Yes or No
hiho,
Heck, I was all ready to agree with Sushmita because I have been using a
convention of having the actor that initiates the use case have a directed
association to the use case in my use-case diagrams. But I am having
trouble finding reference to doing this in any 100% official UML source.
The directed association is a commonly observed pattern in use-case
literature. Applying Use Cases: A Practical Guide by Geri Schneider and
Jason Winters uses directed arrows in each direction between actors and use
cases (see p127 & 177 of the first edition). Furthermore the Rational
University training material for Requirements Management with Use Cases, for
Principles of Object Technology, for Object-Oriented Analysis and Design
with UML, and for Rational Unified Process Fundamentals (phew) all show the
communicates associations pointing from actors to use cases. These courses
mostly only show a directed arrow from an actor to a use case, but here and
there you'll find arrows from use case to actor. You'll also find directed
arrows going each direction in various articles such as this one from
Software Development Magazine
http://www.sdmagazine.com/documents/s=748/sdm0001d/ and this from the
Rational Edge
http://www.therationaledge.com/content/dec_00/t_ucnotfunctions.html
Rational's web-based RUP product specifies in its section entitled
"Guidelines: Communicates-Association": "Each role of a
communicate-association has a navigability property, indicating who
initiates communication in the interaction. Navigability is shown by an
open arrowhead. If the arrowhead points to a use case, the actor at the
other end of the association initiates the interaction with the system. If
the arrowhead points to an actor, the system initiates the interaction with
the actor. Two-way navigability is shown by a line with no arrow-heads."
(v2001A.04.00.13)
But then when I look at the UML Reference Manual I see all bi-directional
associations and no mention of using an association that would point one way
or the other. And I can't find an example or reference to a directed
association in the UML Spec either.
Oh well, I'll still keep using the convention of an arrow from the actor
initiating the use case (disregarding data flow). And I even use arrows
from use cases to secondary actors -- human or otherwise -- to show that the
use case initiates communcation with the actor (again disregarding actual
data flow). The use case diagram is there to communicate requirements and I
like to know who is calling whom.
-------- 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 Eric D. Tarkington
Sent: Wednesday, October 10, 2001 12:28 PM
To: Shukla, Susmita (CICG DTAG)
Cc: ROSE_FORUM
Subject: Re: (ROSE) Use case to actor Yes or No
Susmita Shukla wrote:
> Question: Can a use case "point to" an actor in a use case diagram?
>
> Answer: Yes. This would be a secondary actor. The actor provides
> information needed to execute the use case.
>
> Hope this is simple enough.
>
> Susmita Shukla
It's simple, but wrong, I think. The most important thing is that the
use case diagram cannot indicate the direction of data or control flow
between actors and use cases.
If you want to discuss pointing, you probably need to use an interaction
diagram or an activity diagram.
That's why I discussed the use of actors in the sequence diagram. In
that context, the question is: "Can an object point to an actor in a
sequence diagram?" There, you can say "yes", because the diagram is
capable of doing it.
Once you are talking about the right diagram, you can introduce other
nuances without confusion.
-Eric
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