Ed,
I am familiar with your distinctions of role kinds, it seems to me that there
is also a unification. That these are all "classification in a context". If you
consider each of these roles a type, individuals "play" the role (are of the
type) only in some restricted context - frequently a situation. That context
may be restricted a relation (teacher "sue" teaches student "Sam") or roles in
the context of an organization (Sam is president of the university) or roles in
society based on qualifications and responsibilities (Frank is a policeman, Sue
is a teacher). (01)
The interesting aspect is the relationship between roles at different levels of
context - Sue being a teacher and Sue being Sam's teacher. Certainly these
should be connected, the concepts the same or related. If we look at it in a
"4D sense", perhaps someone is "a teacher" if they ever have or will teach - if
so, is there one role here. We also want to make statements about the more
generic role - "Sue is a good teacher", this would seem to have some connection
to all relationship roles where Sue is teaching. (02)
In a conceptual modeling sense, how many concepts do people hold for roles with
the same term? (03)
So while the role distinctions you call out are interesting, we should also
explore their similarities and relationships. (04)
-Cory Casanave (05)
-----Original Message-----
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[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Edward Barkmeyer
Sent: Friday, October 16, 2015 6:26 PM
To: [ontolog-forum]
Subject: Re: [ontolog-forum] A Question About Mathematical Logic (06)
John, (07)
You have hit upon an issue that has troubled a lot of 'conceptual model' and
'ontology' developers for many years. I would describe that issue as the
ambiguity of the term 'role'. Pat's examples: employee, buyer, seller are
instances of what one might call a 'relational role' (there is probably a more
formal philosophical term). That is, such terms only make sense *relative* to
some specific situation or thing. One cannot be "a buyer"; one can only be "a
buyer of" something. (08)
Student, OTOH, can be a relational role -- one can be a "student of" a given
professor, or a "student at" a given school; but student can also be a
(temporal) class. The class is derived from the relational role by existential
quantification of the related object. Student = a human who is enrolled as a
"student at" *some* school. Museums, for example, often treat students and
'seniors' (another temporal category) as special classes of human when charging
entry fees. (Then again, one might treat 'student' as a specialization of the
relational role 'visitor' in that case, and it might be argued that every use
of the supposed class 'student' is actually a specialization of some other
relational role.) (09)
I have also sometimes found it important semantically to distinguish between a
'participation role' and a relational role. One can be 'the buyer in' a
specific purchase transaction, which is a relationship to the event/situation,
as distinct from 'the buyer of' the item that is purchased in that transaction.
The relationship between the person and the purchased item is derived from the
participation relationship. The concept of 'role' in process modeling is
always a participation. (010)
There is yet another kind of role which we might dub 'reified role', but most
organizations would call a 'position', such as Dean of the Engineering School.
Such a role exists as a thing in the UoD, even when no thing plays the role. (011)
Put another way, the different notions of 'role' can be modeled in OWL as a
Property, a Property slot, a Class, or an Individual, according to what one
intends by the term 'role' and how one expects to use it in making inferences. (012)
I do expect that an expert in one of the cognitive science disciplines can tell
us that 'role' is carefully defined in that discipline and should be used only
with that intent. (In particular, I'm pretty sure Pat used the term carefully,
with the accepted meaning in some discipline.) But the literature of the
information sciences is littered with uses of 'role' that appeal to the
intuition of the reader to determine what is meant. Even worse, some of the
literature "defines" the term in such a way that it is not clear which of the
above is intended. (013)
-Ed (014)
-----Original Message-----
From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F Sowa
Sent: Friday, October 16, 2015 4:31 PM
To: ontolog-forum@xxxxxxxxxxxxxxxx
Subject: Re: [ontolog-forum] A Question About Mathematical Logic (015)
On 10/16/2015 1:44 PM, Obrst, Leo J. wrote:
> Example: Student. Employee. Buyer. Seller. And so on.
> These are roles, and can be characterized in a role hierarchy, if one
> wishes. (016)
I agree that it's important to distinguish roles. In my CS book (1984), I
distinguished them as role type (e.g., Student) vs.
natural type (e.g., Human). Nouns that represent role types have more typical
or expected relationships than those that represent natural types. But natural
types also have expected relationships (e.g., Human vs Elephant vs Rose vs
Cabbage). (017)
> But e.g., Student is not a subclass of Person (or, more clearly Human). (018)
That is a prime example of a typical confusion. The phrase 'more clearly' is a
clue that it's not clear. (019)
A class is normally defined as a set that is characterized by some criterion
that may be stated by a monadic predicate. The students in a school form a set
that may be represented by a monadic predicate. (020)
Q: Why would anyone claim that 'Student' is not worthy of being a class? (021)
A: Some philosopher said so. (022)
Q: Does that distinction make a difference in how the term is
represented in ordinary language? (023)
A: Role types and natural types are both represented as nouns.
But a noun that represents a role may occur in some phrases
that are not expected for a natural type: e.g., "a student
of physics", "a teacher of physics", but it's unusual to say
"a man of physics". In any case, 'unusual' means "unexpected,
but not impossible". (024)
Q: Does it make a difference in how the term is represented in logic? (025)
A: Not in predicate calculus. But some people choose different
ways of making that distinction in some versions of logic. (026)
Q: Does it make a difference in a theorem prover? (027)
A: No. If you represent all the required, expected, and unusual
relationships, you get the same implications. (028)
Q: So why does anyone make that distinction? (029)
A: Because some philosopher said so. (030)
Q: Do all philosophers agree on that point? (031)
A: No. Some say it's a pseudo-problem. Others say there's
a continuum with many borderline cases. (032)
Summary: I have a high regard for good philosophy. But I have little patience
with those who make a fetish of distinctions that don't make a difference in
computing the implications. I have even less patience when those distinctions
create incompatibilities between systems that happen to make different choices. (033)
John (034)
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