W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

RE: Desirata for Symbols (was Re: What do the ontologists want)

From: Ziv Hellman <ziv@unicorn.com>
Date: Sun, 20 May 2001 16:33:26 +0200
Message-ID: <6194CD944604E94EB76F9A1A6D0EDD2310CAEA@calvin.unicorn.co.il>
To: "Sandro Hawke" <sandro@w3.org>, "pat hayes" <phayes@ai.uwf.edu>
Cc: <www-rdf-logic@w3.org>

> pat:
> > sandro:
> > >What possible advantage does "urn:elvis" (or any other 
> URI-like thing)
> > >have over "elvis" as a logic symbol?
> > >
> > >1.  We can prevent unintentional re-use.   This is like
> > >    com.sun.SomeJavaClass or w3c_some_C_library_function.  
> Doing this
> > >    allows us to skip a symbol translation stage in reasoning about
> > >    two different expressions.
> > 
> > Several problems with this include the fact that often, with names, 
> > one NEEDS to have 're-use' in order to refer to something. That is 
> > largely what names are for in social use of language, if you think 
> > about it. But I have argued this to death in earlier threads.
> Er yes -- that's why I said "prevent UNINTENTIONAL re-use."
> In logic terms, I believe this feature lets you make skolum
> functions/constants.

Skolem functions are simply tools for eliminating existential
quantifiers. For example, if one states that in a given population every
person has a brother

(ForAll x) (ThereExists y) Brother(x, y)

then defining a Skolem function f provides a way of expressing a
particular brother in each case -- given x, since you known that x has a
brother, you can use f(x) to refer to "x's brother"

(ForAll x)  [ (ThereExists y) Brother(x, y) --> Brother( x, f(x) ]

Which is all well and good ... but still has no bearing for the question
of 'what possible advantage does "urn:elvis" (or any other URI-like
have over "elvis" as a logic symbol?'


Received on Sunday, 20 May 2001 09:34:23 UTC

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