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Re: [ontolog-forum] Defining everything in terms of relations (was Charl

To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: John McClure <jmcclure@xxxxxxxxxxxxxx>
Date: Tue, 25 Feb 2014 11:39:21 -0800
Message-id: <530CF169.3020205@xxxxxxxxxxxxxx>
Hi Ed,
I agree much with the thrust of your complaint. I'm thinking that the underspecification implicit in a role like 'Teacher' is at the root of a few of the problems you're citing. It surely wouldn't be a recommended practice to subtype Person with Teacher! A computer program can be a teacher too in an educational setting, but surely can never be an assigned-person-to-teacher-role. Anyway, there are different names for such assigned persons, eg Staff Teacher, Substitute Teacher, Special Teacher, Summer Instructor, and so on, rarely just Teacher. It'd sure be interesting to see a hierarchy of Role meta-classes that reflect these different types, eg GenericRole, InheritedRole and AssignedRole to name a few.

On 2/25/2014 10:08 AM, Barkmeyer, Edward J wrote:
Of the above, as a type, only (5) is properly a subtype of whatever kind of thing plays the role. It is a common error to see type (2),(3),(4) roles modeled as subtypes of the class of individuals that can play the role.  Teacher, defined as in (5), is a subtype of person.   ‘teacher of (c)’ where c is a class, i.e., ‘teacher’ as a (2), is not a subtype of person; it is a role of person with respect to a ‘given’ class c.  (teacher(2) is not a unary predicate, it is a function.)  It “becomes” a (5) when you ‘give’ the class c, either as a constant or as an existential, i.e., when you fill the (c) argument slot.  ‘Principal’ is a (4).  It is not a subtype of ‘person’; it is a subtype of ‘organizational position’ and it is related to ‘person’ by something like ‘job of (person)’.  But there is also a role (5) ‘School Principal’, which is the class of persons who hold, or have held, those positions.

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