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Re: [TF-PP] Duplicates and simple property path expressions.

From: Ivan Herman <ivan@w3.org>
Date: Fri, 05 Mar 2010 09:02:46 +0100
Message-ID: <4B90BAA6.2050106@w3.org>
To: Andy Seaborne <andy.seaborne@talis.com>
CC: sparql Working Group <public-rdf-dawg@w3.org>


On 2010-3-4 15:53 , Andy Seaborne wrote:
> In
> http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2010Feb/0018.html
> 
> 
> Rob Vesse observes that "no duplicates" is at odds with the expansion of
> a simple path (a term we have already decided to remove) into a triple
> pattern because there is an implicit projection going on.
> 
>   {?x foaf:knows{2} ?y}
> is not quite the same as
>   { ?x foaf:knows ?z . ?z foaf:knows ?y }
> when there are acylic components/
> e.g.:
> 
> :a foaf:knows :b .
> :a foaf:knows :c .
> :b foaf:knows :d .
> :c foaf:knows :d .
> 
> because ?z is projected away.
> 
> We can specify either way:
> 
> + emphasis that certain property paths are the same as the triple
> expansion form, and not have the striuct no duplicates rule (this
> reintroduces the simple property paths concept) or
> 
> + note, and provide an example, that they are not exactly equivalent.
> 
> I prefer the latter - keep the "no duplicates" situation.
> 

So do I. As a user, who does not know about the algebra and such, having
?x/:a and ?y/:d to the {?x foaf:knows{2} ?y} seems like the natural
answer...

Ivan


> Note this is related to "[TF-PP] cycles - simple or a walk"
> 
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2010JanMar/0455.html
> 
>     Andy
> 
>     Andy
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Friday, 5 March 2010 08:02:35 GMT

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