Dear John, (01)
> MW> So for example, there are ontologies where you will find employee
> > as a subtype of person, and others that understand it is not.
>
> I don't know which way you are advocating, but I'll summarize my
> position:
>
> 1. There is a fundamental distinction between natural types, such
> as Cat or HumanBeing, and role types, such as Pet or Employee.
>
> 2. Every instance of a role type is a subytpe of some natural type,
> but it may also be a subtype of other role types.
> HeartSpecialist
> is a subtype of Physician, which is a subtype of HumanBeing.
>
MW: I do mean that employee is not a subtype of person (or human being). (02)
MW: If we remind ourselves of what being a subtype means, it means that
each instance of a subtype is an instance of the supertype. Now ler us
look at an example. I am an employee of both Shell and Leeds University.
I have different employee numbers, very different salaries, and
different start dates. Now if employee is a subtype of person then
each of these is a person, i.e. there are two of me. (03)
MW: This kind of situation is true of roles generally, you can play
multiple roles at the same time and the same role multiple times
(and at the same time). These do not all generate new people. (04)
MW: So the question is: what is the relationship between a role
and the person who plays is. Fortunately, as a 4-dimensionalist, there
is a simple answer. The role is a temporal part of the person that
plays the role, or if you prefer, the person for a period of time,
rather than for the whole of their life. (05)
MW: This is not so different from the question of the vase and the
piece of clay. Are pots subtypes of clay? Or is the pot a different
object than the piece of clay it is made from? (06)
Regards (07)
Matthew West
Reference Data Architecture and Standards Manager
Shell International Petroleum Company Limited
Registered in England and Wales
Registered number: 621148
Registered office: Shell Centre, London SE1 7NA, United Kingdom (08)
Tel: +44 20 7934 4490 Mobile: +44 7796 336538
Email: matthew.west@xxxxxxxxx
http://www.shell.com
http://www.matthew-west.org.uk/ (09)
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