W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > February 2003

Re: response to semantics comment pfps-01

From: Frank Manola <fmanola@mitre.org>
Date: Tue, 04 Feb 2003 09:10:13 -0500
Message-ID: <3E3FC9C5.9040107@mitre.org>
To: Patrick.Stickler@nokia.com
CC: phayes@ai.uwf.edu, w3c-rdfcore-wg@w3.org

Guys--

This seems like something we could clarify a bit.  On the one hand, we 
have some "explicit characteristics" (to use Patrick's term) we define 
for datatypes to be considered instances of rdfs:Datatype, and which 
these datatypes don't (entirely) possess.  On the other hand, we seem to 
say that any of these datatypes need to be processed by "datatype-aware" 
processors that grok both RDF and the datatypes in question, and are 
capable of doing useful things with them (consistent with the semantics 
of the datatypes).  Now, presumably XML Schema processors can do useful 
things with those datatypes, so it must be possible to build other 
processors to handle those datatypes in appropriate ways, whether they 
satisfy the characteristics we've identified for rdfs:Datatypes or not. 
    So, given that we, in effect, "hand off" processing the datatypes to 
separate processors that are suppoed to be fully capable of handling 
them (whatever their definitional defects as far as RDF is concerned), 
what is the problem?  I'm not denying that there may *be* a problem, but 
it seems to me could clarify this some.  This would seem to be of 
particular interest to people who are interested in using RDF together 
with datatypes *other* than XML Schema datatypes, that aren't defined 
according to its abstract framework (which we claim they can do).

--Frank

Patrick.Stickler@nokia.com wrote:

>  
> 
>     -----Original Message-----
>     From: ext pat hayes [mailto:phayes@ai.uwf.edu]
>     Sent: 04 February, 2003 00:51
>     To: w3c-rdfcore-wg@w3.org
>     Subject: response to semantics comment pfps-01
> 
>     Some XML Schema primitive datatypes are impossible to use as RDF
>     datatypes.  Therefore XSD intepretations are ill-defined.
> 
>     The problematic datatypes include:
>     duration - because equality in its value space is not well defined
>     QName - because there is no fixed lexical-to-value mapping
>     ENTITY - because there is no fixed value space
>     NOTATION - because there is no fixed lexical space
> 
>     ----
> 
> 
>     I don't consider these to be fatal problems which make it
>     'impossible' to use these datatypes.  
> 
>  
> 
> I'm not particularly confortable with that statement. RDF Datatyping is 
> based on explicit characteristics
> 
> which should be embodied by each and every member of rdfs:Datatype. If 
> some XML Schema datatype
> 
> fails to have any of those characteristics, then they are not valid 
> instances of rdfs:Datatype and I
> 
> would expect not usable with RDF. I.e., I would consider those to be 
> fatal problems.
> 
>  
> 
> To use a datatype with RDF, i.e. to specify it as the value of the 
> attribute rdf:datatype is to assert that
> 
> it is a member of rdfs:Datatype. And to assert that a datatype is a 
> member of rdfs:Datatype is to
> 
> assert that it has a value space, a lexical space, and an N:1 mapping 
> from lexical to value space
> 
> where N >= 1.
> 
>  
> 
> Thus rdf:datatype="&xsd;ENTITY" would be an error, if so asserted, as it 
> in fact has no fixed value
> 
> space, etc.
> 
>  
> 
>      
> 
>      What is true however is that these are examples of
>     *underdetermined* datatypes, ie datatypes about which the available
>     information is incomplete in some way.
> 
>  
> 
> My hope is that it is the specs which are incomplete and that the XML 
> Schema WG could clarify the definitions
> 
> of these datatypes in a manner that would allow them to be treated as 
> valid members of rdfs:Datatype.
> 
>  
> 
> 
>     For example, the set of durations is underdetermined; what this
>     means is that *any* set which conforms to the XSD spec will suffice
>     as a value space of xsd:duration, and there may be more than one
>     such set. There may therefore be more XSD interpretations than the
>     XML authors intended. As usual in such situations, the effect on
>     inference is that some inferences simply cannot be made, eg it is
>     simply unknown whether or not one xsd:duration literal can be
>     substituted for another, so to this extent the corresponding
>     inference rule does not apply. The text makes it clear that these
>     rules apply only in cases where certain kinds of information are
>     provided by the datatype information source.
> 
> 
>     In sum, I don't think there is any need to do anything about this
>     issue, except possibly to add some explanatory prose to clarify the
>     point.
> 
>  
> 
>  
> 
> Explanations, yes, but let's be careful about exactly what we're saying.
> 
>  
> 
> Cheers,
> 
>  
> 
> Patrick
> 
> 
>     Pat
> 
> 
> -- 
> 
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-- 
Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Tuesday, 4 February 2003 08:51:11 EST

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