[Modeling] Modeling an Agent Class- register your opinion

[Dr. Hong Zhu]

Gerd,

The point is: the destroying of the whole (i.e. a department) cause the
parts (i.e. the members) to lost its class membership to an 'agent class'
(i.e. member of the department). What I am saying is that, the definition of
part-whole relationship in UML in terms of shareability is not adequate.
Even shareability plus lifetime cannot define the kind of part-whole
relationship we need to deal with agent's part-whole relationships.

I agree with you that, in agent-orientation, shareability does not imply
lifetime dependency. However, I think, in object orientation, shareability
does imply lifetime dependence. Because, if a part object is not shareable,
then when the whole object is destroyed, the part objects become garbage. It
life is then also finished. Am I right?

-Hong

----- Original Message ----- 
From: "Wagner, G.R." <G.R.Wagner@tm.tue.nl>
To: "Dr. Hong Zhu " <hzhu@brookes.ac.uk>; "Wagner, G.R."
<G.R.Wagner@tm.tue.nl>; "James Odell " <email@jamesodell.com>; "ModelingTC "
<modeling@fipa.org>
Sent: Thursday, June 19, 2003 5:57 PM
Subject: RE: [Modeling] Modeling an Agent Class- register your opinion


> > The relationship between the department and it members is different from
> > composite in UML, because the agent is still alive after the owner is
> > destroyed. It is also different from aggregation because the destroy of
> > the owner (the department) affects the behaviour of the member agents
(they
> > lost the membership of department members and the associated capability
and
> > accessible resources). If an object is a part of another object as an
> > aggregate, the destroy of the owner will not affect the part object's
> > membership to any class, so does not affect its behaviour.
>
> Hong,
>
> again, the difference between aggregaion and composition is simply
> the property of shareable parts. The property of lifetime dependency
> you refer to is orthogonal to this.
>
> Obviously, in your example, there is an aggregation relationship between
> the members of a department  and the department (because a member
> can be also a member of another department, i.e. members can be
> shared). An aggregation relationship does not imply anything wrt
> lifetime dependency and it does neither imply that it would not affect
> its parts. These are additional, othogonal issues.
>
> So, your conclusion that we need a "third" part-whole relationship is
> unfounded.
>
> -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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