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Back to Has-A [was UML Question]

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Fri, 6 Jun 2003 11:50:28 -0500
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E01817E69@bocnte2k3.boc.chevrontexaco.net>
To: michael.mahan@nokia.com, martin.chapman@oracle.com, www-ws-arch@w3.org

Very useful, Mike.  Thank you.

Somewhat amusingly, it seems to me that this reference contains simple,
if slightly inscrutable, definitions of "has-a", "is-a" and "comprises".
Notably:

<quote>
[triangle] ... identifies derivation The derived class is the base
class, but with additional (or modified) properties. Derived (sub) class
is a specialization of (extends) the base (super) class.

[open diamond] ... Aggregation (comprises) relationship. Destroying the
"whole" does not destroy the parts. 

[solid diamond] ... Composition (has) relationship. The parts are
destroyed along with the "whole."
</quote>

Although slightly cryptic in our context, these definitions seem clear
enough to me to move forward with -- at least until finding a situation
where they are confusing.  I realise that they don't have the
philosophical rigor that Frank is drawn to, and they may be more rooted
in programming constructions than might be strictly comfortable -- but
at least they are a LOT better than NOTHING.  Although the "destroys"
seems to refer to what happens in memory when a program runs, if I kind
of squint my eyes a bit it seems to me that the "has-a" relationship
implies a dependency of the children on the parent that need not be
there in the "comprises" relationship.  I believe that this was probably
the basis of the objection to my use of the term "has-a" in Rennes.

-----Original Message-----
From: michael.mahan@nokia.com [mailto:michael.mahan@nokia.com] 
Sent: Friday, June 06, 2003 8:40 AM
To: Cutler, Roger (RogerCutler); martin.chapman@oracle.com;
www-ws-arch@w3.org
Subject: RE: UML Question


Roger,

* means 0 or more. 

Here's a crib sheet:

http://www.holub.com/goodies/uml/index.html

MikeM

>-----Original Message-----
>From: ext Cutler, Roger (RogerCutler) 
>[mailto:RogerCutler@chevrontexaco.com]
>Sent: June 05, 2003 10:02 PM
>To: Martin Chapman; www-ws-arch@w3.org
>Subject: UML Question
>
>
>
>Martin -
>
>Do the *'s in your diagram (at least, I think that's what they are, 
>although with the font you are using it's hard to tell) mean
>
>1 - 0 or more (as in regular expressions)
>
>2 - 1 or more (like + in regular expressions)
>
>3 - Something completely different
>
>I am guessing 2 or conceivably 3 because you seem to have an explicit 
>0..., but I'd like to check because that seems a bit odd to me.  
>Perhaps this is just because I've written a lot of Perl code.
>
>
>
Received on Friday, 6 June 2003 12:52:45 GMT

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