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Re: [TF-PP] Scoping the design space

From: Paul Gearon <gearon@ieee.org>
Date: Tue, 29 Sep 2009 10:03:59 -0400
Message-ID: <a25ac1f0909290703q8efd688rd4d3ed26a781ef5d@mail.gmail.com>
To: SPARQL Working Group <public-rdf-dawg@w3.org>
On Tue, Sep 29, 2009 at 6:20 AM, Alexandre Passant
<alexandre.passant@deri.org> wrote:
> HI,
>
> On 15 Sep 2009, at 13:38, Seaborne, Andy wrote:
<snip/>
>> Having access to the length of the path needs to say what happens for
>> loops and for multiple paths between the same two graph nodes.
>
> While imo relatively useful, I also agree that using path length can be
> tricky in many cases, esp. combined with entailment.

Only if the predicate is considered transitive (the issue that you
demonstrated in your email). But I don't believe that path length
makes sense for a transitive predicate, since the path length is
always "1", by definition. Instead it becomes useful for other
predicates, particularly non-transitive subproperties of transitive
predicates.

For instance, family:hasAncestor is transitive, so path lengths don't
make sense, but the sub-property family:hasFather is non-transitive
and the path length makes a lot of sense. foaf:knows is another
example, this time without a transitive super-property.

So if a predicate is being treated as transitive, then the path must
be 1 or 0, but otherwise it could be useful.

Paul
Received on Tuesday, 29 September 2009 14:04:42 GMT

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