John, (01)
If you look at some of the standard textbooks on data modelling you will
find that: (02)
a) They recognise that some systems fudged the distinction between employee
and role (as you note)
b) that it is not a good idea to do it, and
c) offer their own way of modelling this. (03)
My experience with legacy systems re-engineering is that not all (or even
many modern) systems make this mistake. But am sure my sample is not
representative. (04)
See (for example),
Data Model Patterns: Conventions of Thought by David C. Hay
http://www.amazon.com/Data-Model-Patterns-Conventions-Thought/dp/0932633293/
ref=pd_bbs_2/002-8927839-5907206?ie=UTF8&s=books&qid=1174246335&sr=8-2 (05)
The Data Model Resource Book, Vol. 1: A Library of Universal Data Models for
All Enterprises by Len Silverston
http://www.amazon.com/Data-Model-Resource-Book-Vol/dp/0471380237/ref=sr_1_1/
002-8927839-5907206?ie=UTF8&s=books&qid=1174246404&sr=1-1 (06)
(As an aside, I seem to recall Matthew West's 'High Quality Data Models
paper' notes this - or something similar as a common modelling error -
Matthew can confirm whether this is the case.) (07)
To return to an old topic: one can regard employee as a role or a temporal
stage of a person - depending upon your 3D/4D inclinations. A description of
the 4D approach is in my book. (08)
http://www.amazon.com/Business-Objects-Re-Engineering-Computer-Professional/
dp/075062082X/ref=sr_1_1/002-8927839-5907206?ie=UTF8&s=books&qid=1174246688&
sr=1-1 (09)
Regards,
Chris (010)
-----Original Message-----
From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F. Sowa
Sent: 18 March 2007 14:27
To: [ontolog-forum]
Subject: Re: [ontolog-forum] Common Logic Controlled English (CLCE) (011)
Peter, (012)
That's the way most businesses handle their personnel: (013)
> Since when is an "employee" a sub-type of "person"?! (014)
However, one of the major mining companies used mules
to pull ore out of the mines. (They didn't want to use
anything that might create sparks that could trigger
an explosion if there were any stray gasses around.) (015)
When they computerized their system, they assigned
employee numbers to the mules. For that company, you
could generalize the ontology in either of two ways: (016)
1. Assume that Employee is a subtype of Animal. (017)
2. Assume that Person could include nonhuman animals. (018)
But in any case, whenever you say X is a subtype of Y,
you mean "every X is a Y." That is all it says. (019)
John (020)
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