Re: [RDF+OWL] Way of connecting RDF and RIF lists

Sandro Hawke wrote:
>> http://www.w3.org/2005/rules/wiki/RIF-RDF-Lists
> 
> 1.  Does the rdf graph need to include the 'rdf:type rdf:List' triples?
>     I hope not.
> 
> That is:
> 
>    ex:a ex:p _:l1 .
>    _:l1 rdf:first ex:b .
>    _:l1 rdf:rest rdf:nil .
> 
> entails:
> 
>    ex:a[ex:p -> List(ex:b)].

It was my interpretation that in RDF the list items (_:l1, etc) must be
of type rdf:List to have a well-formed list. Therefore, in the original
proposal, if you use simple or RDF entailment, these triples are required.
When checking the RDF documents again, I realize that there is not much
support for this interpretation.
I modified my proposal to get rid of this requirement.  So, your test
case is now valid.


> 
> 
> 2.  Can I provide my RDF data in RIF frames?  I hope so (at least in the
>     one-to-one mapping version).
> 
> That is:
> 
>    import(any-rdf-graph-even-an-empty-one, rdf-simple).
> 
>    ex:a[ex:p -> _:l1].
>    _:l1[rdf:first -> ex:b].
>    _:l1[rdf:rest -> rdf:nil].
> 
> entails:
> 
>    ex:a[ex:p -> List(ex:b)].

Yes, this works in both the extension and the one-to-one semantics.

> 
> 
> 
> 3.  Is an RDF list without a final rdf:nil just an open RIF List?  I'd
>     kind of expect so, although I don't really care.   
> 
> That is:
> 
>    ex:a ex:p _:l1 .
>    _:l1 rdf:first ex:b .
>    _:l1 rdf:rest ex:c .
> 
> entails:
> 
>    ex:a[ex:p -> List(ex:b | ex:c)].

Right now, rdf:nil is required, and so this test case is not valid.

Actually, according to the RIF list semantics, List(ex:b | ex:c) does
not necessarily denote a list.  In some interpretations it will be a
list, and in other interpretations it is just some object.
This might actually be a problem.

That said, it is possible to require the existence of some list (denoted
by ex:c) in this case. However, I do not fully understand the
consequences of such a change at the moment.

Anyway, I think it is reasonable to require rdf:nil, because in all RDF
documents that mention lists, lists are closed, and the special RDF/XML
syntax for lists requires them to be closed.

> 
> I'm not sure about the case where the 3rd triple is totally missing; it
> seems like the open list would still exist, even if we can't name its
> tail.
> 
> In the one-to-one version, I'd expect open lists to map to RDF lists
> with some kind of variable 'rest' part:
> 
>    ex:p(List(ex:a | ?X)).
> 
> entails
> 
>    Exists ?x ?rest (
>       And(
>          ex:p(?x) 
>          ?x[rdf:first -> ex:a] 
>          ?x[rdf:rest -> ?rest]
>          ))

Yes.


Best, Jos


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Jos de Bruijn,        http://www.debruijn.net/
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