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Re: Another thing on property paths...

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Fri, 17 Dec 2010 10:54:55 +0000
Message-ID: <4D0B417F.5030802@epimorphics.com>
To: Axel Polleres <axel.polleres@deri.org>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
What changes to

http://www.w3.org/2009/sparql/docs/query-1.1/rq25.xml#defn_evalZeroPath

are you proposing?

On 17/12/10 09:53, Axel Polleres wrote:
> Independent from Jorge's remarks on the comments list, I have had another
> question on PropertyPaths, particulary about ZeroLengthPath:
>
>
> Admittedly, find the e.g. the zeroLengthPath operator quite unintiuitive at the moment,
> linking *ALL* nodes with each other...
> that means that e.g.
>
> ?X knows* ?Y

In the real work probably meant

?X knows+ ?Y

> for not only the transitively linked pairs of resources via the knows property,
> ALL pairs of nodes in the graph... Actually, I isn't a more standard way of treating 0-length paths just as
> reflexive, i.e. only linking each node reflexively with itself?

It's a possibility.

Do you have pointers to the "more standard way"? (noting that there 
isn't an implied forward or backwards direction to arcs in an RDF 
graph).  ^:p is related to the intuition of the (not currently legal) 
:p{-1}.

> I would at least find this more intuitive and returning less noisy results, i.e. "what I can reach from one node
> in 0 steps is just the node itself" sounds intuitive to me. Am I mistaken here? If yes, why?
> At least, I don't understand why we *need* to return the pairs of all nodes here?

It does not *need* to - it's a choice point in the design provdiing it's 
consistent with the cases of:

?X knows* <Y> ==> ?X=<Y>

and

<X> knows* ?Y ==> ?Y=<X>

	Andy
...

>
> Can someony explain to me why the reflexive only version of ZeroLengthPath wouldn't work with the rest?
>
> Axel
Received on Friday, 17 December 2010 10:55:34 GMT

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