[Modeling] Modeling an Agent Class- composition
Thu, 26 Jun 2003 13:27:20 +0200
>>> Maybe a better example is that: when a person is an employee
>>> of a company, where both the employee and the company are agents,
>>> and the person is a part of the company. When the compnay
>>> goes bust, (i.e. the agent company is destroyed), the person
>>> lost his job and become an umployed.
>>> Which part-whole relation of UML is applicable to this situation?
>> Why should this not be aggregation (with shareable parts)?
>> It has the form
>> Person isPartOf Company [playingTheRoleOf Employee]
>> It's shareable since a person can be employed by many
>> companies (at the same time).
> Shared or not shared is about whether one entity can be a part of
> many others entities. Lifetime is about whether the part will be
> killed when the whole is killed. Am I right?
Yes, you are.
> If yes, then, none of the above features tells that if a part
> quit from the whole or the whole is destroyed (it is possible
> in dynamic classification), what happens to its roles played
> in the whole.
Yes, this question refers to additional properties of the
aggregation relationship. An aggregation, and also a compositiom,
can have lifetime dependency (= inseparability of parts) or not.
What is your problem? Would you like to be able to specify
this lifetime dependency in a model? Then you can use a Boolean-
valued tag "inseparable=true" for the part association end (as
proposed in the paper mentioned below).
We can simply define such as tag in our AUML Profile. But
it is not related to the distinction between agents and objects;
it applies to all composed entities.
> ----- Original Message -----
> From: "Wagner, G.R." <G.R.Wagner@tm.tue.nl>
> To: "Stephen Cranefield"
> <email@example.com>; "ModelingTC"
> Sent: Thursday, June 26, 2003 9:19 AM
> Subject: RE: [Modeling] Modeling an Agent Class- composition
> > > Hong Zhu wrote (on 19 June):
> > >> We have a agent that represents a department in a university,
> > >> and a number of agents as members of the department. When the
> > >> department is destroyed, ...
> > > Composition seems to work perfectly well to me.
> > Yes, I don't see any problem either.
> > And contrary to Hong's appeal, we cannot rely on the UML2 spec for
> > the semantics of aggregation/composition (especially wrt lifetime
> > dependency), because it is unclear/confused and not well-defined.
> > They say themselves:
> > -----------------
> > Semantic Variation Points (p.40 of the current UML2 document)
> > The precise lifecycle semantics of aggregation is a semantic
> > variation point.
> > Semantic Variation Points (p.75 of the current UML2 document)
> > Precise semantics of shared aggregation varies by application
> > area and modeler.
> > ------------------
> > So we better rely on well-justified theories of the part-whole
> > relationsip, such as sketched in my paper
> > Towards Ontological Foundations for UML Conceptual Models
> > http://tmitwww.tm.tue.nl/staff/gwagner/ODBASE-2002.pdf
> > which is also a recommended reading in OMG's RFP for an Ontology
> > Definition Metamodel.
> > -Gerd
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