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RE: hasa in UML

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Fri, 30 May 2003 21:54:06 -0500
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E01817E5F@bocnte2k3.boc.chevrontexaco.net>
To: "Francis McCabe" <fgm@fla.fujitsu.com>, www-ws-arch@w3.org

Good grief.

I had assumed from Martin's posting that aggregation is a well-known,
standard term in UML.  If it is, and you have just missed it, perhaps he
should chime in.  If not ...

If not, perhaps somebody -- anybody -- could give us some rough idea
what "has a" means to UML people?  I recall that the UML folk seemed to
be real clear (well, at least Martin seemed to be real clear) that
usages of "has a" consistent with your definition were inconsistent with
UML usage -- so surely SOMEBODY must have some idea why or how????  If
it is clearly different, could somebody give a hint in what way it is
different?

If not -- could we please just forget about it?

On another tack -- did your definitions of "is-a" and "has-a" just come
out of your imagination, or are they consistent with some standard usage
in a discipline other than UML?  If the latter, would it be possible to
provide citations?

-----Original Message-----
From: Francis McCabe [mailto:fgm@fla.fujitsu.com] 
Sent: Friday, May 30, 2003 4:42 PM
To: www-ws-arch@w3.org
Subject: hasa in UML



UML does not, in fact, has a direct notion of aggregation.

There are three concepts that might be pressed into the service of 
aggregation:

Association (3.41 and following)
Composite Object (3.40)
Collaboration diagrams (3.65 and following)

Association is simply a relationship. There is no additional semantics 
built-in. We can define our own form of association called has-a (but 
we are trying to avoid that right?)

"A composite object represents a high-level object made of tightly 
bound parts. This is an instance of a composite class, which implies 
the composition aggregation between the class and its parts. A 
composite object is similar to (but simpler and more restricted than) a 
collaboration; ..."

I do not think that this meets our needs. It is not accurate to say 
that a service is composed of X + an identifier.

Collaborations on the other hand are not what is going on either:

"A collaboration is used for describing the realization of an Operation 
or Classifier."

Frank

On Friday, May 30, 2003, at 02:10  PM, Cutler, Roger (RogerCutler) 
wrote:

>
> Well, that's progress of a sort.  Now what do "generalization" and 
> "aggregation" mean, and how does this differ from the current 
> definition?
>
Received on Friday, 30 May 2003 22:54:27 GMT

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