[Modeling] Modeling an Agent Class- register your opinion

[Wagner, G.R.]

> I am now more confused about UML's aggregation. The definition of
> aggregation kinds in UML 2.0 is far from clear. 

I agree. It's confused.

> It states that the compoite object has responsibility for the existence 
> and storage of the composed objects (parts)'. 

This is just a  confusing remark. Better don't take it serious. In one
sentence they say, that the components must be destroyed whenever
the composite is destroyed (this is inseparability), but in the next
sentence they say that it would be also OK to attach the component to
another composite (this would be the property of a mandatory whole)  
The real defining property of  composition is that it is a kind of aggregation 
with *non-shareable* parts. Those other properties (inseparable part and
mandatory whole etc.) are orthogonal to it.

> Could you please let me know your web address so that I can download
> your paper?

Please use google and search for "Gerd Wagner" (I'm currently on holidays
and  don't know my web page by heart :-)

> However, I feel that you have missed my point, which is, the aggregation
> kinds in UML seems not suitable for agents. 

Why should this be so? I didn't get the point.

> There are only two disjoint aggregation types in UML no matter how they are 
> defined, but we need a third type for agents.

Why?

-Gerd


----- Original Message ----- 
From: "Wagner, G.R." <G.R.Wagner@tm.tue.nl>
To: "Dr. Hong Zhu " <hzhu@brookes.ac.uk>; "James Odell "
<email@jamesodell.com>; "ModelingTC " <modeling@fipa.org>
Sent: Tuesday, June 17, 2003 9:03 PM
Subject: RE: [Modeling] Modeling an Agent Class- register your opinion


> > The part-whole relationship between agents are also different:
> > The aggregation relationships between the whole and part is
different in
> > agent classes from that in object class. In object orientation,
there
are two
> > types of whole-part relations:
> > (1) composition, in which the lifespan of the whole and the part is
the
> > same, and (2) aggregation, in which the lifespan of the whole and
part
> > is independent. Having two whole-part relations is inadequate for
> > agent-orientation due to agent's autonomous behaviour. For example,
we
> > have a agent which represents a department in a university, and a
number
of
> > agents as members of the department. When the department is
destroyed,
> > the members as individuals still exist, but their class membership
as
the
> > member of the department are lost.
>
> This is a misunderstanding of the UML aggregation concept. Composition
> is defined as a "non-shareable" aggregation, and not via lifetime
dependency.
> There are some misleading remarks about lifetime dependency in UML
1.4.
> Lifetime dependency is implied in aggregations with inseparable parts.
> It's not related to shareability. Please see my ODBASE'2002 paperr on
> ontological foundations of UML (on my homepage) for further
explanattions.
>
> Of course, all general ontological isssues of the part-whole
relationship
> apply to all things, no matter if they are agents or objects.
>
> -Gerd
>
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