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Re: Question regarding subselect

From: Axel Polleres <axel.polleres@deri.org>
Date: Thu, 30 Apr 2009 21:24:06 +0100
Message-ID: <49FA08E6.9020606@deri.org>
To: Steve Harris <steve.harris@garlik.com>
CC: Simon Schenk <sschenk@uni-koblenz.de>, SPARQL Working Group <public-rdf-dawg@w3.org>
If have a related question. Do we really talk only about subSELECTS or 
should we - more generally speak about subQUERIES.

I have the impression, that also ASK and CONSTRUCT subqueries in 
Specific places make sense, like:

CONSTRUCT subqueries in FROM/FROM NAMED clauses

SELECT ...
FROM {CONSTRUCT ... }
WHERE

ASK subqueries in FILTERS

SELECT ...
WHERE { pattern FILTER( !ASK {...} )}

agreed? The latter would, BTW, be an alternative way to express negation.

Axel


Steve Harris wrote:
> On 30 Apr 2009, at 11:48, Simon Schenk wrote:
>> If we do not add any features such as aggregates, scalar expressions, 
>> assignment
>> or similar - do subselects add anything to the expressiveness of the 
>> language?
>> All examples in the wiki include at least one such additional feature.
>>
>> Typical uses such as FORALL or EXISTS should be possible in the 
>> current version
>> of SPARQL using a combination of OPTIONAL, BOUND filters and perhaps 
>> DISTINCT, I
>> think.
> 
> There's nothing you couldn't do with multiple queries before. But, you 
> can do new things using DISTINCT and LIMIT inside the subselect in one 
> query, that's enough to do LimitByResource in many cases, which you 
> can't do without SubSelects.
> 
> Example off the top of my head (may be incorrect):
> 
> SELECT *
> WHERE {
>   ?x a foaf:Person
>   SUB {
>     SELECT ?name
>     WHERE { ?x foaf:name ?name }
>     LIMIT 1
>   }
>   SUB {
>     SELECT ?mbox
>     WHERE { ?x foaf:mbox ?mbox }
>     LIMIT 4
>   }
> }
> 
> Currently we don't implement sub queries, so we end up doing something 
> like 20, where 1 would be fine.
> 
> - Steve
> 


-- 
Dr. Axel Polleres
Digital Enterprise Research Institute, National University of Ireland, 
Galway
email: axel.polleres@deri.org  url: http://www.polleres.net/
Received on Thursday, 30 April 2009 20:24:46 GMT

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