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Re: Input sought on datatyping tradeoff

From: Jerome Euzenat <Jerome.Euzenat@inrialpes.fr>
Date: Fri, 12 Jul 2002 12:45:13 +0200
Message-Id: <a05111b09b9545d71e93e@[]>
To: Brian McBride <bwm@hplb.hpl.hp.com>, "Thomas B. Passin" <tpassin@comcast.net>, www-rdf-logic@w3.org


In his message (Re: Input sought on datatyping tradeoff) of 12/07/2002,
Brian McBride wrote:
>>[Brian McBride]
>>  >    <Jenny> <ageInYears> "10" .
>>>     <Jenny> <testScore>  "10" .
>>>  Should an RDF processor conclude that the value of Jenny's ageInYears
>>>  property is the same as the value of Jenny's testScore property?
>>[Thomas B. Passin]
>>I do not think this question is well posed.

I might be a bit aside here. But, what an RDF processor is entitled 
to conclude?

I would consider two options:
- sets of (RDF-)triples
	(or, it is able to answer yes/no to a query which is a set of
		RDF triples,
	 or, it is able to answer by an assignment to ...);
- arbitrary (or defined somewhere) predicates
	(or, it is able to answer yes/no to a query which is a ...,
	 or, it is able to answer by an assignment to ...);

In the former, the answer to Brian's question is "no" because the 
query is not an RDF-triple (the first component is a litteral).

In the latter, it depends on the querying predicate. For equality (of 
values) I would say "yes" if both litterals have the same (or 
comparison-compatible) type(s). So, as Tom presented it, this is for 
Schema-aware processors. Schema-unaware processors, if they cast 
everything to "string" would answer "yes". And this raises another 
problem: we often think that a Schema-aware processor will enable to 
conclude more fact than a Schema-unaware one... Here we will have 
something strange: The Schema-unaware processor concludes equality, 
where the Schema-aware concludes inequality (in case the case of the 
film-title example). So do Schema-unaware processor do not conclude 
anything about litterals?

>Secondly, consider a query processor which queries an RDF graph 
>based on subgraph match:
>   ?x <ageInYears> "10" .
>   ?x <testScore> "10" .
>where the intent of the query is to find the x's where the denotions 
>of the values of the properties are the same.

Isn't the intent of this query better given by:

?x <ageInYears> ?y .
?x <testScore> ?y .

  Jérôme Euzenat                  __
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Received on Friday, 12 July 2002 06:45:49 UTC

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