John:
I don't think you read to the end of my post, and I would contend that
my general point is still valid. (01)
As to the specific example: my main irk is that the process is awry: if
a mule can be considered as a person, then something is seriously out of
kilter. Your modeller is no longer modelling the real world but
attempting to re-create the world to fit his/her model. My message would
be: "Dear modeller: get out a bit more..." Both a mule and a human play
the *role* of employee in your example, they are *not* both subtypes of
person. (You could push out the boat further, and argue about the
concept "employee" when applied in this context - I'm sure they would
have had fun "explaining" to the IT systems that the mule doesn't get a
pay check or statement, is not enrolled in healthcare, etc.). If you
establish as an axiom that "every employee is a person" then, sure, it's
going to go bust when you have non-people as employees. It's like the
European Commission having to classify a carrot as a fruit because,
according to their *policy* (and there's the key) "jams and marmalades"
are defined as being manufactured from fruit. The fundamental error was
in the original definition not in the subsequent, and necessary, twist
on reality needed to preserve (no pun intended) the policy when carrot
jam came on the market. (02)
Facts change over time, so do roles. Laws do not. You state that, (03)
"By definition, X is a subtype of Y if and only if
every instance of X is also an instance of Y" (04)
This must always be true or it isn't a definition, it's a
time-constrained assertion. applying your definition, it is not always
true that employee is always a subtype of person, unless you move the
goal posts. And in most formal rule-based games, that's called cheating.
A lot of modellers cheat because it's easier to get the job done. If
reality rears its ugly head, then tell reality to take a hike. But "what
a wicked web we weave, once we started to deceive"... (05)
The issue for me is not about the rights and wrongs of logic. It is
about the good and the bad of modelling practices. (06)
All the best, (07)
Peter (08)
-----Original Message-----
From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F.
Sowa
Sent: 18 March 2007 18:18
To: [ontolog-forum]
Subject: Re: [ontolog-forum] Ontology and methodology (new thread off
"Common Logic Controlled English (CLCE)") (09)
Peter, (010)
Are you sure that you are interpreting the word "subtype"
the way it is usually used? (011)
By definition, X is a subtype of Y if and only if
every instance of X is also an instance of Y. (012)
Therefore, "Employee < Person" or "Employee is as subtype of Person"
means nothing more nor less than every employee is a person. (013)
That is certainly true of most businesses. And if you wish to
allow mules to be considered persons, it would also be true
of the mining company. (014)
John (015)
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