W3C home > Mailing lists > Public > public-rif-wg@w3.org > February 2008

Re: ACTION-432: ugly ill-formed literals use case...

From: Axel Polleres <axel.polleres@deri.org>
Date: Fri, 22 Feb 2008 11:42:09 +0100
Message-ID: <47BEA701.7050509@deri.org>
To: Michael Kifer <kifer@cs.sunysb.edu>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>

Michael Kifer wrote:
>> Ok, here another use case where one might get ill-formed literals.
>>
>> I have some RDF data.
>>
>> :a :age "old".
>> :b :age "33".
>> :c :age "young".
>> :d :age "88".
>>
>> and want to write a rule which converts the untyped
>> literals to xsd:integer typed ones where possible.
>>
>> Ideally, I would like to have the option to write something in
>> RIF like:
>>
>>    ?X[:age->&ex:createTypedLiteral(?Y,"xsd:integer"^^xsd:anyURI)] :-
>>        ?X[:age->?Y] and &isInteger(?Y).
>>
>> where ex:createTypedLiteral is a built-in function creating
>> a typed literal from a string and a datatype IRI and
>> isInteger is a type checking builtin.
>>
>> Now if I drop the last condition
>>
>>    ?X[:age->&ex:createTypedLiteral(?Y,"xsd:integer"^^xsd:anyURI)] :-
>>        ?X[:age->?Y].
>>
>> I will get ill-formed literals. :-(
>>
>>   you might argue, that functions to "construct"
>> new literals are not so nice, but I think in practical
>> RDF transformation use cases they are important.
>>   Well, one could argue also of course that the definition of
>> ex:createTypedLiteral should be in a way that returns an error
>> on an ill-formed result... but I don't know whether we can prevent that, 
>> if we allow built-ins to be extensible.
> 
> A constructor should return valid literals. So, it should give an error here.

basically that is what I discussed with Jos.
Maybe we should have in the datatypes and built-ins document that:

- new datatypes have to define their lexical and value space.
- any built-in function are expected to return only well-formed literals
- any built-in predicates should return an error when any of it's 
argument is bound to an ill-formed literal
- the predefined interpretation of any built-in predicate should not 
include any tuple involving ill-formed literals

ok? because that is what I we have to put in rather the
BLD or the DTB document?

... all that might relate to the just ongoing error-discussion.

Axel

-- 
Dr. Axel Polleres
email: axel@polleres.net  url: http://www.polleres.net/

rdfs:Resource owl:differentFrom xsd:anyURI .
Received on Friday, 22 February 2008 10:42:35 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 2 June 2009 18:33:45 GMT