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Re: ISSUE-48: Less verbose delete syntax

From: Andy Seaborne <andy.seaborne@talis.com>
Date: Mon, 23 Nov 2009 13:38:17 +0000
Message-ID: <4B0A9049.1060609@talis.com>
To: Steve Harris <steve.harris@garlik.com>
CC: "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>


On 23/11/2009 10:53, Steve Harris wrote:
> On 22 Nov 2009, at 16:05, Andy Seaborne wrote:
>
> [snipped a lot]
>
>> My current preference is:
>>
>> DELETE WHERE { X }
>>
>> where X is BGPs + GRAPH + FILTER.
>>
>>
>> (The question for me is more whether we should do less, not more, than
>> that.)
>
> I think my preference is BGPs + GRAPH only. Possibly no bNodes too,
> depending on what the exact semantics of bNodes are in this case.
>
> I'm not really adverse to FILTER, but I have systems where optmising
> DELETE WHERE { ?x a <Foo> } etc. is really easy, but
> WHERE { ?x a ?type . FILTER (REGEX(STR(?type), "Foo")) } (i.e. anything
> that doesn't trivially optimise down to algebra expressions) is hard to
> do. Personal bias :)
>
> Would be nice to have some form of DELETE that will always be fast,
> relative to the amount of data it has to remove.

If there is a FILTER, then it can be more work but if no FILTER is 
mentioned, there is no reason it should get in the way.  So FILTER-less 
should be fast for you.

With just BGP+FILTER, the FILTER is always the outermost and easy to find.

GRAPH changes that but then you don't need the FILTER to get complicated:

DELETE WHERE { ?x a <Foo> ; :p ?o. GRAPH ?g { ?y a <Bar> ; :p ?o} }

There's an argument that we need a "no join" restriction (join across 
quad patterns) and so it's always of the form:

   filter?
     graph?
       BGP

for optional filter and graph at the algebra level.

Because it's rather easy to detect the fast forms, I think restricting 
the syntax is not the right way to go.  A clear description as 
BGP+GRAPH+FILTER from query patterns is easier to explain (and possibly 
parse/detect).

	Andy


>
> - Steve
>
Received on Monday, 23 November 2009 13:38:42 GMT

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