DAMl "Thing" should be Top, Universal class - including concrete types

From: Tim Berners-Lee (timbl@w3.org)
Date: 01/30/01

I am concerned about the suggestions that what DAML
calls a daml:Thing, and RDF (unfortunately) a rdf:Resource
should not include concrete types.

I feel RDF should be fixed so that literal strings are regarded
as particular resources, and I think even a mapping into URI space
should be specified using the "data:" scheme which has been defined
exactly for this purpose.  (<data:logic/rdf;10> = "10")

But the main point of this email is to counter suggestions that
concreete types and abstract types should be made quite distinct
and properties only be allowed to hve a range and domain
which are subclasses of one or the other.

The basic fundamental raeson why this is bad is that it is not minimalist
design.  It is fine for an individual project, but for the semnatic web
it can't be an assumption you force in theunderlying infrastructure.
Essentially this says, "All things, whatever they are are one of two
distinct classes, at a more fundamental level than any other
distinction".  This sort of statement must only be made when it
is absolutely necessary to create an infrastructure which will stand up
on its own feet.

It is more difficult to give examples which will appeal to an arbitrary
as to why one might need properties whose range or domain contain both
abstract and concrete types.

One example is the title of a book.  The property foo:title, say related
an abstract work and something which is a human-oriented description
of it.  A simple use is to say

title(mybook, "The cat in the hat")

A more complicated use is to say

title(mybook, mybooktitle)
english(mybooktitle, "The cat in the hat")
french(mybooktitle, "Le chat dans le chapeau")   %%  or whatever

Annother is that I might genericly want to write logic to deal with the
values of fields in an address book.  I might want to talk about the
validity and caretion date and author of fields and their
values, when some values are concrete (date of birth, an xmldt:date)
and some are complex (office, a location, which has properties
such as address and phone number and so on).

I actually find the idea so odd that I find it difficult to explain why it
weird.  It shows how different woldviews can be, I suppose. I hope this
makes sense.

If the logic is set up so that there is no set which includes both leaves
and branches, we have an arbitrary constraint underpinning all our
work, and I find that unacceptable.  Unless I have missed something.


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