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Re: Test cases for blank node label scope - and a case for discussion

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 29 Jan 2007 10:08:16 -0600
Message-Id: <p06230901c1e3cc230cac@[192.168.2.2]>
To: Steve Harris <steve.harris@garlik.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>On 28 Jan 2007, at 20:51, Seaborne, Andy wrote:
>
>>Attached are some tests (positive and negative) for reuse of blank 
>>nodes labels only within BGPs.
>>
>>There is one case to point out: syn-bad-39.rq
>>
>>{
>>    _:a ?p ?v .  FILTER(true) . <x> ?q _:a
>>}
>>
>>1/ By the principle that FILTERs apply to the whole group, it could 
>>be taken as like:
>>   { _:a ?p ?v . <x> ?q _:a . FILTER(true) }
>>which is one BGP.
>>
>>[Filter true
>>   [BGP
>>     _:b0 ?p ?v
>>     <x> ?q _:b0
>>   ]]
>>
>>2/ By the principle that BGPs are adjacent triple patterns, it has 
>>appearance as if it were two BGPs like:
>>
>>   { BGP( _:a ?p ?v . ) FILTER(true) BGP( [] ?q _:a . ) }
>>
>>so it would be:
>>[Filter true
>>   [Join
>>     [BGP _:a ?p ?v]
>>     [BGP <x> ?q _:a]
>>   ]]
>>which is illegal (_:a spans BGPs).
>>
>>Blank node labels can't appear in FILTERs so this also makes sense 
>>by saying FILTERs end the blank node label scope.
>
>I prefer (1), but then I also think it's less confusing to require 
>FILTERs be at the end of the BGP.
>
>To me it doesn't visually at all obvious that the FILTER divides the 
>BGP into two:
>
>{
>   something1 .
>   something2 .
>   something3 .
>}
>
>looks like one BGP, whether or not if something2 is a FILTER.

Yes. Particularly as the order of triples in a group isn't relevant, 
so why should the order of filters be?

Pat

>
>- Steve


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Received on Monday, 29 January 2007 16:08:26 GMT

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