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Re: Reification of Sets (of RDF Statement, for Queries)

From: Graham Klyne <GK@ninebynine.org>
Date: Wed, 11 Apr 2001 11:09:08 +0100
Message-Id: <5.0.2.1.2.20010411105142.03dbf460@joy.songbird.com>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-interest@w3.org
Sandro,

I think there may be a problem with this, if you are proposing defining a 
vocabulary of sets in the RDF core.

I don't think it makes sense much sense to talk about sets in RDF without 
talking about the properties of sets, and operations on sets.  At least, 
the concept of equality of sets that you touch on.  I think it's fairly 
clear that RDF core defines (at least) an abstract syntax.  And the 
constructs corresponding to x={4,3} and x={3,4} are clearly syntactically 
different.

The definition you suggest depends upon an _interpretation_ of the RDF 
statements into the constructs of set theory (and I think I'm using that 
term in a correct model theoretic sense).  I think it would be premature to 
try and define such an interpretation without first having clear 
interpretations for the more fundamental constructs of RDF.

I think it may be fine to define a vocabulary for sets, with associated 
interpretation, that is not part of the RDF core.  This view is based on an 
idea that the RDF core is ultimately only an abstract syntax, without 
semantics (which I agree is not universally held, but I suspect that this 
is the way that the RDF-logic discussion is leading:  half-hearted 
semantics is worse than no semantics).

#g
--

At 07:24 PM 4/9/01 -0400, Sandro Hawke wrote:

>Issue 1: RDF M&S Does Not Provide Sets
>
>The argument against them I've heard is "we don't have an enforcement
>mechanism" (for duplicates, so use bags) or "we have to provide them
>in some order" (so use lists).
>
>I think those arguments against defining a vocabulary for
>communicating information about set membership are, to put it mildly,
>weak.
>
>On the first point, you don't need to provide an enforcement
>mechanism.  If someone says "X contains 3" and then "X contains 3"
>again, well, you know "X contains 3".  No problem.
>
>On the second: it doesn't matter if you have extraneous data.  In set
>theory, people say "x={3,4}" and they know it's the same as "x={4,3}".
>Yes, syntacticly the elements appear as a list, but the set whose
>elements were enumerated by the list is the name no matter what order
>of enumeration is used.  The extraneous ordering information is simply
>ignored.
Received on Wednesday, 11 April 2001 07:52:29 GMT

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