Matthew, (01)
Sorry to resume with one of your messages from far back in this
thread. But this matter did not clear up subsequently, in my
mind at least, and it still bothers me. (02)
On 19 March you were answering PatC:
>> "Employee" is also a subtype of Person,
>
> MW: Now there you go and spoil it. If employee is a subtype of
> person, it means that each instance of employee is a separate
> instance of person, i.e. there are two of me. There is a
> relationship between employee and person of course, but you
> need to let go of the popular myth that it is
> subtype/supertype. (03)
I must confess to subscribing to that "myth"! And certainly, as
you say, it is popular, being a classic or textbook example of
OO's inheritance. (04)
I am sure that there must other ways of interrelating Employee
and Person (even assuming that by Person we mean HumanBeing),
but I cannot for the life of me see how the subtype relationship
should imply your second sentence above, which I extract and
quote again: (05)
> If employee is a subtype of person, it means that each
> instance of employee is a separate instance of person, i.e.
> there are two of me. (06)
In my book (and certainly in MACK) in such subtyping there are
not at all two separate instances (except perhaps in a RDBMS
with a historical legacy of separate and uninterrelated
relations for Employee and Person), but one instance of two
types, just as any entity at all can be (and in MACK virtually
always is) an instance of many types, with or without a subtype
relationship between any pair of them. As is often said, "A
type is merely a predicate." And some predicates can specialize
others. (07)
And of course polymorphism and the Liskov Substitution Principle
apply, in recognition of the singular nature of the entity with
the multiple IsA relationship. And a search on Employee or
Person would reveal just one result in respect of any one
individual. And the identity criteria for Person would apply to
Employee too, even though Employee might have further criteria
(as in "the Manager of Department X"). (08)
I also find that "4D" has no bearing on the matter, even though
the Employee status or predicate might only hold for a limited
period of time. At least in MACK, dynamic subtyping is even
happening literally all the time, as change is the irreducible
measure of time and every new predicate is always a candidate
for triggering further state changes, so no new subtyping = no
change = no perceptible time! (09)
Furthermore, all the above is timeless in the sense of PatH's
criterion which I have already approvingly quoted (in my "2nd
instalment" of Feb 21) in this way: (010)
> .Pat Hayes had earlier insisted (now at
> http://ontolog.cim3.net/forum/ontolog-forum/2008-01/msg00385.html)
> that
>
>> The ideal ontology framework is one in which all
>> contextual sensitivity has been _eliminated_ as far as
>> possible. (011)
(There, of course, I regard time-dependence - or "lack of
timelessness" - as part of PatH's "contextual sensitivity".) (012)
That whole perspective just seems to me so plain and simple and
everyday (even though for this forum I describe it with the help
of some fancy words!).. (013)
Furthermore, as such, that setup well satisfies the
intelligibility criterion that PatH drew to our attention with
this (also on March 19) in this thread: (014)
> There are formal inconsistencies, which can be detected by
> logical machinery. But there are also what one might call
> mismatches, where a formal ontology, while internally
> consistent, fails to conform to a human user's intuition so
> strongly that it becomes incomprehensible to them. Typically
> this is what gives rise to formally incompatible ontologies,
> when they are separately developed by folk with these
> divergent intuitions.
>
> Simply being internally consistent does not guarantee that an
> ontology is intuitive or even comprehensible. (015)
PatH's comment was not directed specifically at the issue I
raise here, but it certainly should apply to it, and I maintain
that (in PatH's words) your view "fails to conform to a human
user's intuition so strongly that it becomes incomprehensible
to" me at least! (016)
(Or, PatH, am I misinterpreting you in those two quotes of your
words above?) (017)
But that's enough from me on the subject. Please, Matthew, let
me (and - I don't doubt -others) have the benefit of your
perspective here? (018)
Christopher (019)
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