# Re: More on XSD in RDF

From: pat hayes <phayes@ai.uwf.edu>
Date: Sat, 30 Nov 2002 21:57:20 -0600
Message-Id: <p05111b0aba0cefd4dcf4@[10.0.100.247]>
To: Jan Grant <Jan.Grant@bristol.ac.uk>

```
>On Tue, 26 Nov 2002, Patrick Stickler wrote:
>
>>     xsd:decimal rdfs:subClassOf xsd:float .
>
>This isn't true, because 0.1 does NOT occur in the xsd:float value
>space. (it's 2^-1 . 5^-1)
>
>>     xsd:float rdfs:subClassOf xsd:decimal .
>
>This is true if floats and decimal value spaces are just sets of
>numbers, as Jeremy described.

In mathematics, there is no such thing as a 'float'. The term was
invented for use in programming, and refers to a mode of
*representation*, not to a kind of number. So to just blandly assume
that it is obvious that the sets of 'floats' and 'decimals' are
supposed to be subsets of the positive rationals, is being very
casual with what might well be a rather delicate distinction, seems
to me. Many systems and even quite a few textbooks take it as obvious
that floats and integers, for example, are *disjoint* sets of
entities; SpecWare, the leading program-property proving logic,
assumes strong typing in which for example the real number zero and
the integer zero are considered to be distinct numbers. Some set
theoretic FOM formalizations make distinctions like this, and
category theory would also treat them as distinct entities (in
different categories, with morphisms between them.) In all of these
cases the subClassOf relationship above would be firmly rejected. I
honestly have no idea what XML schema thinks the relationship between
floats and decimals is, even after reading the specs. You can
understand phrases like 'set of numbers' in more than one way,
depending on what you think 'numbers' are. So I think we should be
careful, is all, not to jump the gun over issues like this. The
answers are NOT obvious from the published specs. At the very least,
we should refer such questions to a suitable authority. I really
don't think that we should be saying anything that depends on an
*interpretation* of the XSD spec. Instead, we should try to be very
clear what information we expect a datatype spec to give an RDF
engine, and what RDF takes it to mean, and then we should let the
authors of the XML Schema spec tell us what that information actually
is for the XSD class of datastructures. If that requires them to do
some more work, then fine, but let them do that work, not us for
them. We might very well get it wrong, and in any case we don't have
either the time or the authority to do it for them.

Pat

>
>
>--
>jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
>Tel +44(0)117 9287088 Fax +44 (0)117 9287112 http://ioctl.org/jan/
>"My army boots contain everything not in them." - Russell's pair o' Docs.

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Received on Saturday, 30 November 2002 23:53:57 UTC

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