[Modeling] Modeling an Agent Class- register your opinion

Dr. Hong Zhu hzhu@brookes.ac.uk
Wed, 18 Jun 2003 08:56:24 +0100

Hi, Gerd,

I am now more confused about UML's aggregation. The definition of
aggregation kinds in UML 2.0 is far from clear. It states that 'composite
indicates that the property is aggregated compitely, i.e. the compoite
object has responsibility for the existence and storage of the composed
objects (parts)'. Does 'existence' means lifetime? If a composite is
deleted, how could it be responsbile for the existence of the parts?

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

However, I feel that you have missed my point, which is, the aggregation
kinds in UML seems not suitable for agents. There are only two disjoint
aggregation types in UML no matter how they are defined, but we need a third
type for agents.


----- 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
> > agents as members of the department. When the department is destroyed,
> > the members as individuals still exist, but their class membership as
> > 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
> 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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