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Re: Action needed: subClassOf on datatypes

From: Graham Klyne <gk@ninebynine.org>
Date: Tue, 02 Sep 2003 16:00:45 +0100
Message-Id: <>
To: pat hayes <phayes@ihmc.us>, w3c-rdfcore-wg@w3.org

I agree and prefer (a) or (c), whichever presents best.  I incline towards 
(a), mainly as I'm not sure how we do test cases for "(D-)consistency".


Just saw Jan's post:

I'm happy with that, which (I think) is effectively (c).

[can't find the WG archives for September to replace above reference]


At 20:08 01/09/03 -0700, pat hayes wrote:

>Guys, this is to point out a recently identified buglet in the datatype 
>semantics and to outline  alternative ways to deal with it. Mia culpa for 
>not catching this earlier, but we need to fix it somehow.
>Recall that we weakened the conditions on rdfs:subClassOf a while back, so 
>that being a subset was a necessary but not sufficient condition for being 
>a subClass. This means that the inference rule rdfD4  is not valid, since 
>even ddd's value space is a subset of eee's value space and they are both 
>datatypes, it still doesn't necessarily *follow* that one is an 
>rdfs:subClassOf the other.
>This means in turn that the text case we discussed 2 weeks ago which says that
>xsd:integer rdfs:SubClassOf xsd:number .
>is XSD-entailed by the empty graph, is wrong. In fact, the only subclass 
>assertions which follow from the empty graph are those of the form
>aaa rdfs:subClassOf aaa .
>aaa rdfs:subClassOf rdf:Resource .
>even in D-interpretations.
>I can think of four ways to fix this.
>(a) modify the test case doc by deleting the test case;
>(b) modify the test case to say that this only follows under the 
>strengthened extensional semantic conditions on rdfs:subClassOf described 
>in section 4.1 of the semantics document;
>(c) modify  the test case to say that the case is D-consistent with the 
>empty graph, not that it is D-entailed by it;
>(d) modify the semantics of D-interpretations to insist that datatype 
>class subsetting *is* treated extensionally, so that the rule rdfD4 is 
>valid and the test case is OK. This can be done by adding the following 
>semantic condition on D-interpretations:
>if <aaa, x> and <bbb, y> are in D and the value space of x is a subset of 
>the value space of y, then <x,y> is in IEXT(I(rdfs:subClassOf))
>I would vote against (b), and think that (c) is wimpy; I think (a) (or (c) 
>) is the best solution, but would be willing to go with (d) if the WG 
>feels that we *ought* to impose extensional conditions on datatype 
>classes.  In rule terms, do y'all think that rdfD4 *ought* to be a valid 
>rule (ie to be undeniably true under all circumstances), or would it be 
>better to allow people to make, but also be free to not make, subClassOf 
>assertions about 'external' datatypes? I like that latter approach, 
>myself, because it is more in line with the intensional approach we have 
>adopted generally, and it neatly sidesteps issues involving identity 
>versus equality and other wierd stuff that seem to arise in XSD 
>discussions. On the other hand, it means work for some other editors, 
>rather than for me.
>I have versions of the semantics document ready for both alternatives (a 
>or c) and (d).
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Graham Klyne
Received on Tuesday, 2 September 2003 11:15:04 UTC

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