[Versa] Issue 1, better literal and datatype support

[Michael Olson]

On Aug 12, 2005, at 7:23 AM, Chimezie Ogbuji wrote:

> On 8/12/05, Michael Olson <Mike.Olson at fourthought.com> wrote:
>>
>> I'd like to propose adding better literal and data type support to
>> Versa.  I don't think we need to do too much to the spec itself to
>> support this.  One thing we need is a literal data type.  This would  
>> be
>> a representation of a plain (with or without language) or typed
>> literal.  I think we leave hard issues like comparison and sorting
>> between typed literals to the underlying model.  If the model support
>> D-entailment then it can properly compare "01"^^xsd:int and
>> "1"^^xsd:int.  If it doesn't....
>
> I had exactly the same suggestion.  So your suggestion a literal
> datatype as a *replacement* for strings and numbers?

No.  I still think numbers are important in Versa

eq(.,5) as an example.  My suggetion is that literals become the  
objects of statements in versa.

> If so, I'd
> agree, since that would completely cover all literals (especially if
> we include the capablity to associate xsd - or other - datatypes to
> the underlying model) and would be more inline with RDF Literals.
>

Right.  But Versa does not do anything extra WRT XSD.  For example, it  
just asks the model, are these literals equal.

>> Besides the addition of the literal datatype, I think all that is
>> needed is to determine how the conversions work (should be pretty
>> straight forward) and some functions.  ie. it would be nice to filter
>> on language and/or datatype in a traversal.
>
> Luckily, I think there is alot of precedent on this (with XQuery's use
> of datatypes and SPARQL's - the latter simply burrows from XQuery):
>
> http://www.w3.org/TR/xpath-functions/#casting-from-primitive-to- 
> primitive
>
>> One last thing, we would need to allow these literals as "subjects" in
>> traversals.  This does not mean much from the specification point of
>> view, maybe just a mention, but implementors will need to understand
>> this.
>
> I agree, and I think this becomes neccessary once you allow datatyping
> because of RDFs entailment rules
> (http://www.w3.org/TR/rdf-mt/#simpleRules  - rdfs1) and RDF Literals.
>
> Specifically:
>
> uuu aaa lll (where lll is a plain literal (with or without a language  
> tag)
>
> implies
>
>  _:nnn rdf:type rdfs:Literal .
>
> where _:nnn identifies a blank node allocated to lll by rule rule lg.
>
> So, the literals themselves are thought of as resources by the RDF
> model (especially if they are typed)

Even if they are not types (as you show above).

Mike

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Mike Olson                                                Principal  
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