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RE: Literals: lexical spaces and value spaces

From: <Patrick.Stickler@nokia.com>
Date: Wed, 14 Nov 2001 13:57:44 +0200
Message-ID: <2BF0AD29BC31FE46B788773211440431621793@trebe003.NOE.Nokia.com>
To: phayes@ai.uwf.edu
Cc: w3c-rdfcore-wg@w3.org, pfps@research.bell-labs.com


> -----Original Message-----
> From: ext Pat Hayes [mailto:phayes@ai.uwf.edu]
> Sent: 14 November, 2001 03:39
> To: Stickler Patrick (NRC/Tampere)
> Cc: w3c-rdfcore-wg@w3.org; Peter F. Patel-Schneider
> Subject: RE: Literals: lexical spaces and value spaces
> 
> 
> >........
> >>  >This, of course, presumes that we are not asserting the
> >>  >global constraint on data types that the lexical space of
> >>  >any data type must be a proper subset of the lexical space
> >>  >of all of its superordinate types.
> >>
> >>  Ah, but we must make that assumption; I have already conceded
> >>  that point.
> >
> >But XML Schema simple data types fail that requirement. Thus,
> >we cannot make that assumption. Only value spaces for XML
> >Schema simple types are proper subsets of the value spaces
> >of their superordinate types. Lexical space is specific to
> >each type. I had hoped that was not the case, but it is.
> 
> Can you please elaborate on this point, with an example, as it seems 
> rather important.
> 
> I was under the impression that XML Schema datatypes DID satisfy the 
> required conditions. To fail, we need the following circumstances: 
> two datatypes D1 and D2 with the value space of D1 being a subset of 
> that of D2, and the lexical space of D1 intersecting that of D2, and 
> D1 having a different, and incompatible, lexical-to-value mapping on 
> that intersection from that used by D2.

If we consider only lexical spaces, none of the lexical spaces for types 
derived-by-list (NMTOKENS, IDREFS, and ENTITIES) are proper subsets of 
the lexical spaces of their immediate superclasses.
 
If we consider canonical lexical spaces, then in addition to the above,
none of the canonical lexical spaces of xsd:integer and its subclasses
are proper subsets of the canonical lexical space of xsd:decimal.

Finally, such a constraint would prohibit the definition of e.g. a
subclass of xsd:integer -- e.g. scm:integer -- that has a perfect
intersection with regards to value space but does not have a lexical
space that is a perfect subset of xsd:integer.

Thus, to enforce that the rdfs:subClassOf relation between data type
classes includes proper subset intersection of lexical spaces not
only excludes XML Schema as-is, but also the means by which disparate
data type schemes can be related in terms of value space.

Cheers,

Patrick
Received on Wednesday, 14 November 2001 06:57:50 EST

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