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RE: isa and hasa in UML

From: <Daniel_Austin@grainger.com>
Date: Fri, 30 May 2003 14:25:36 -0500
To: martin.chapman@oracle.com
Cc: fgm@fla.fujitsu.com, RogerCutler@chevrontexaco.com, www-ws-arch@w3.org, www-ws-arch-request@w3.org
Message-ID: <OFE5D51454.F1A594CE-ON86256D36.006A88C4@grainger.com>

UML isn't exactly the model we want to emulate anyhow; and set theory -
well, that's simply trying to boil the world's biggest trout pond. I've
spent my entire career thinking about set theory (and the continuum
hypothesis) and it's still trout to me...let's not go there.



Dr. Daniel Austin
Sr. Technical Architect / Architecture Team Lead
daniel_austin@notes.grainger.com <----- Note change!
847 793 5044
Visit http://www.grainger.com

"If I get a little money, I buy books. If there is anything left over, I
buy clothing and food."

                      "Martin Chapman"                                                                                           
                      <martin.chapman@o        To:       "Cutler, Roger (RogerCutler)" <RogerCutler@chevrontexaco.com>, "Francis 
                      racle.com>                McCabe" <fgm@fla.fujitsu.com>, www-ws-arch@w3.org                                
                      Sent by:                 cc:                                                                               
                      www-ws-arch-reque        Subject:  RE: isa and hasa in UML                                                 
                      05/30/2003 01:33                                                                                           

and how is is-a and has-a as defined in our doc any less or more powerful
than uml.
its all about set theory and if you choose to model bad sets thats up to


> -----Original Message-----
> From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On
> Behalf Of Cutler, Roger (RogerCutler)
> Sent: Friday, May 30, 2003 10:43 AM
> To: Francis McCabe; www-ws-arch@w3.org
> Subject: RE: isa and hasa in UML
> This is REALLY discouraging.  I thought that the UML experts in the room
> at Rennes were saying that "everybody knows" what has-a means in UML,
> and all you have to do is strip it out of your favorite undergraduate
> textbook.
> I have a strong feeling of distaste for ditching the definition of
> "has-a" currently in the document, which at least has the virtue that I
> can understand and apply it, in favor of a definition that appears to be
> like the Indian rope trick -- something that everybody knows exists
> because somebody else has seen it.
> -----Original Message-----
> From: Francis McCabe [mailto:fgm@fla.fujitsu.com]
> Sent: Friday, May 30, 2003 12:01 PM
> To: www-ws-arch@w3.org
> Subject: isa and hasa in UML
> This is in partial fulfillment of my action item re is-a and has-a
> w.r.t. UML
> 0. There is a rather (unintentionally) funny comment in the UML 2.0
> spec:
> Semantics
>    The meanings of the constructs are defined using natural language.
> ...
> (This is after a lot of promises of being formal.)
>    However, UML uses OCL for those cases where natural language is not
> enough. OCL is similar to a first order predicate calculus. Having said
> that, the spec does not use OCL very often; including for the
> definition of relationships such as generalization (is-a) and
> association (has-a kind of)
> 1. As I have indicated earlier, UML does not have a precise notion of
> is-a. The closest is the generalization relationship. This is defined
> in 3.50:
> Generalization is the taxonomic relationship between a more general
> element and a more specific element that is fully consistent and that
> adds additional information.
> A couple of comments:
> 1. Basing is-a on taxonomics raises some serious logical issues. This
> is analogous to basing everything on sets: every member of the penguin
> set is also a member of the bird set.
> The problem is that it becomes really difficult to talk about weird or
> abstract sets. Basing is-a on this would lead to the following
> counter-intuitive result: every unicorn is a yeti. (There are no
> documented instances of either, so the set of unicorns and yetis is
> indistinguishable.)
> A more serious issue, sticking with birds for the moment, is that it is
> similarly hard to talk about properties of birds such as flying: we
> could not express the fact that all birds except penguins fly.
> An even more serious issue is that we need to capture the following
> situation:
> A service has an identifier
> A Web service is a service
> A Web service has a URI
> The Web service's URI counts_as the service identifier
> It is that counts_as that is beyond the capabilities of UML's
> generalization. We *could* extend UML's generalization, and that may be
> the best overall approach. In fact, we would really need to do that for
> all our relationships, use <is-a> and <has-a> and *never* rely on UML's
> built-in relationships. <is-a> and <has-a> could probably be defined in
> OCL.
> More to follow....
> Frank
Received on Friday, 30 May 2003 15:25:27 UTC

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