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Re: Further comments on SPARQL 1.1 (property paths)

From: Andy Seaborne <andy.seaborne@talis.com>
Date: Fri, 26 Feb 2010 14:29:16 +0000
Message-ID: <4B87DABC.4080303@talis.com>
To: Rob Vesse <rav08r@ecs.soton.ac.uk>
CC: public-rdf-dawg-comments@w3.org


On 25/02/2010 3:24 PM, Rob Vesse wrote:
> With regards to my previous comments and the Working Groupís response
> [1] I would like to make some further comments.
>
...
> Property Paths Ė Having asked Steve Harris for clarification of this
> off-list Iíd like to make the following comment about simple property
> paths. The draft states that simple paths can be transformed to algebra
> expressions and executed as such (Iíve implemented this in my
> implementation) but the specification also states that property paths
> should eliminate duplicates. In the case where paths can be transformed
> to a BGP is it still necessary to eliminate duplicates?

A simple path is one that is equivalent to writing out in full in triples.

For example:
?x :p/:q ?y

is equivalent to:

?x :p ?_Z
?_Z :q ?y

for some variable generated ?_Z

A BGP does not generate duplicates nor does a simple path.

So if the transformation has been done to a BGP, no more work is needed 
other than to evaluate the BGP.

	Andy

>
> Rob Vesse
>
> PhD Student
>
> IAM Group
>
> Bay 20, Room 4027, Building 32
>
> Electronics & Computer Science
>
> University of Southampton
>
> SO17 1BJ
>
> [1] http://www.w3.org/2009/sparql/wiki/CommentResponse:RV-2
>
Received on Friday, 26 February 2010 14:29:39 GMT

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