On Sun, Jan 22, 2006 at 11:26:52AM -0500, John Sowa wrote:
> 5. The word 'type' has a long history of use as a technical
> term whose meaning was very close to its use as a common
> English word. Unfortunately, Bertrand Russell gave it a
> very narrow sense in logic, which caused many logicians
> to introduce the word 'sort' with a slightly different
> technical sense. Meanwhile computer language designers
> adopted the word 'type' for the kinds of data structures
> used in their systems. All these uses fall within the
> scope of the informal senses of the word 'type', and it
> seems possible to adopt 'type' as a generalization that
> would include all the technical senses and most, if not
> all of the common senses. (01)
The notion of "type" in ramified type theory falls within the scope of
the informal senses of "type"? You appear to be drawing upon the usage
of a very sophisticated community of speakers of informal English! (02)
> 6. In another unfortunate twist, the object-oriented group
> adopted the word 'class' to distinguish their thingies,
> which have associated procedures called 'methods', from
> the more static data types of the older languages. More
> recently the Semantic Webbers adopted 'class' for the
> thingies used in OWL, but as Chris, Michael, and others
> have pointed out, OWL also uses the word 'type', (03)
More exactly, OWL incorporates the term "rdf:type" from the RDF
language. And, contrary to your implications, there is no problem with
that whatsoever. As clearly and explicitly stated in the OWL model
theory, "rdf:type" denotes a relation whose range is rdfs:Class.
owl:Class is, in general, a subclass of rdfs:Class, and the two are
explicitly identified in OWL Full. (04)
It's pretty clear that the anti-W3C philosophers around here haven't
done their homework. These languages are expressively limited and
rather horrible to look at, but they have a lot of important virtues,
are in wide adoption, and are ignored by this group at its peril. (05)
> and all of its definitions are very confused and confusing. (06)
The documentation often leaves a lot to be desired, but the syntax and
model theories for the W3C languages are not the least bit confused or
confusing (aside from being a bit of a trial to slog through). John,
when you speak out against the W3C languages without really
understanding them, as you evidently do not, you are misusing your
authoritative position in this community. (07)
> The major argument for using the word 'class' is that it has
> been adopted by the Semantic Web movement, which currently
> has a great deal of momentum. But one could also say that
> the Semantic Web has also adopted the word 'type' in a way
> that seems to be very closely linked to the word 'class'. (08)
Yes, closely linked in pretty much exactly the same way that
"instance-of" is. Do you have a problem with *that* connection? (09)
> Summary, I strongly believe that the word 'class' is the
> *worst* possible choice to represent the intensional side
> of the distinction between intensions and extensions:
>
> 1. Logicians use the word 'class' in the same extensional
> sense as the word 'set'. (010)
Right, that is due to how they axiomatize the terms. We would not adopt
the same axioms. (011)
> 2. Object-oriented programmers use the word 'class' as
> something that has associated procedures, and that
> is definitely *not* a meaning we want to suggest. (012)
OO programmers are also smart enough to know when they are programming
and when they are reading an ontology. (013)
> 3. The OWL group uses both 'class' and 'type' in ways that
> are related, but it seems safe to say that there is
> probably nobody in the OWL community who could give
> a clear argument for any distinction between them. (014)
Actually, just about anyone in the OWL community could. And I gave you
the precise difference between them above. What is safe to say is that
you are irresponsibly trashing the W3C languages when you don't really
know what you are talking about. (015)
> In short, the distinction between intension and extension
> is fundamental to ontology, and it *must* be highlighted.
> The word 'class' would hopelessly confuse the issue. (016)
Properly axiomatized, it simply wouldn't. I can't believe that the
members of this ONTOLOGY and Taxonomy Coordinating WG have so little
faith in the power of axioms -- you know, like in an ontology -- to
clarify the meaning of so fundamental a term. If people want to know
what a class is, they'll look at the axioms, just like any other term.
What do you people believe, anyway? (017)
I fear this group is looking less and less like a WG and more and more
like other ideological war zones we've seen over the past 15 years. (018)
-chris (019)
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