W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > November 2001

Re: heading toward datatyping telecon

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Mon, 5 Nov 2001 20:25:09 -0600
Message-Id: <p05101032b80cf5508524@[65.212.118.166]>
To: Patrick.Stickler@nokia.com
Cc: w3c-rdfcore-wg@w3.org
>
>The lexical validity of sub-types with regards to their super-types
>is important in the context of ontological transparency whereby
>a given value may be defined in terms of a very specific data
>type yet a given query (and the resultant knowledge) is defined
>in terms of a more general data type, and the response must be
>encoded in a *lexical* form that is valid.
>
>Thus, it is not acceptable to e.g. create a sub-type hexInteger
>of type integer which has a lexical form that is invalid for
>integer because a system may recieve a query for the value of
>a property that has a range of 'integer' yet the knowledge
>is defined via a sub-property having a range of hexInteger, and
>the resultant response would encode a hexInteger literal as
>the value of a integer property, which is invalid.

Wait a minute. How could this happen, again? Suppose indeed I define 
a datatype class called xxd:hexInteger which is a rdfs:subClassOf 
Integer, say. .And suppose that the property eg:hexish is defined to 
have hexIntegers as its range:

eg:hexish rdfs:range xxd:hexInteger .

And suppose the graph also contains

aaa eg:hexish "37" .

 From which it follows that the value of hexish on aaa is 55, in the 
MT extension, but we get a query like:

aaa eg:hexish _:x .
_:x rdf:type Integer .

Then, if I follow your point, it would be erroneous to return the 
binding _:x/"37", since neither the query nor the response would 
indicate the datatyping information which tells one that this numeral 
should be understood to mean 55 rather than 37. Is that right? But 
this is indeed a binding that would satisfy the query, following the 
usual rdfs closure rules for subClassOf.

Please confirm if I have this right, because it does indeed seem like 
a rather serious matter for the proposed modification to the model 
theory, which would only work if the datatype scheme satisfies the 
mandatory validity of instances of subclasses, which you tell us XML 
Schema does:

>Thus, per the XML Schema specification, a nonNegativeInteger
>lexical form is also a valid integer lexical form is also a valid
>decimal lexical form, etc. These data types are very well defined,
>and the hierarchical equivalence issues were obviously well
>understood by the folks who wrote it -- and of course, the whole
>concept of manditory validity of instances of sub-classes in
>super-classes is at the very heart of the XML Schema model. Sub-types
>are defined only be restriction, not by deviation which does not
>conform to all superclasses. This characteristic should *not*
>be discarded by RDF in the interpretation of literals by defined
>data type by assuming that rdf:type only applies to value space
>and not also to lexical space.

Pat

PS. I now understand why you reacted as you did to the 
octal/decimal/binary examples, and I see your point.
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Received on Monday, 5 November 2001 21:25:10 EST

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