Re: Wishlist for SPARQL 1.2: Compatible query-hints, extra math operators

A few points:

 *   Prefix hints alone are not sufficiently rich.  We use "virtual triples" so we can influence specific joins, sub-groups, sub-selects, etc.
 *   We use a namespace for hints so people can identify any bigdata specific dependencies in their queries.
 *   Query hints sometimes are necessary for an application to "work". This might mean having reasonable performance, but it also might mean accessing a vendor specific functionality.  A very similar problem arises if you have a SERVICE that interprets the graph pattern as having specialized semantics.  E.g., as supporting full text, geospatial search, other sorts of "extension" services.
 *   Even if you have standard hint syntax (which would be nice), the semantics of the hints will not be standard and hence applications will still not be portable.

One suggestion would be to introduce a marker (similar to the "#" character for comments) that indicates that the triple pattern is a query hint.  This would make it possible for the hints to be automatically ignored if they do not pertain to a specific platform (e.g., because the hints are not in an understood namespace for that platform).

To draw an example from the link to our wiki below [1], you might use the "%" character to mark the triple pattern as a query hint (we do not currently recognize that syntax – this is just an example to indicate what I mean).


PREFIX rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?x ?o
WHERE {

  # disable join order optimizer for this group graph pattern.
%  hint:Query hint:optimizer "None" .

  ?x rdfs:label ?o .
  ?x rdf:type foaf:Person .
}


Thanks,
Bryan
[1] http://sourceforge.net/apps/mediawiki/bigdata/index.php?title=QueryHints

From: william greenly <william_greenly@hotmail.com<mailto:william_greenly@hotmail.com>>
Date: Tuesday, July 30, 2013 10:15 AM
To: "Jerven. Bolleman" <jerven.bolleman@isb-sib.ch<mailto:jerven.bolleman@isb-sib.ch>>, "public-sparql-dev@w3.org<mailto:public-sparql-dev@w3.org>" <public-sparql-dev@w3.org<mailto:public-sparql-dev@w3.org>>, "public-rdf-dawg-comments@w3.org<mailto:public-rdf-dawg-comments@w3.org>" <public-rdf-dawg-comments@w3.org<mailto:public-rdf-dawg-comments@w3.org>>, Kingsley Idehen <kidehen@openlinksw.com<mailto:kidehen@openlinksw.com>>, Bryan Thompson <bryan@systap.com<mailto:bryan@systap.com>>
Subject: RE: Wishlist for SPARQL 1.2: Compatible query-hints, extra math operators

Excellent - Yes! SPARQL 1.2. If we want to follow in the footsteps of SPARQL 1.1 we should ensure 1.2 has lots of major changes in protest against semantic versioning.

> Date: Tue, 30 Jul 2013 16:05:27 +0200
> From: jerven.bolleman@isb-sib.ch<mailto:jerven.bolleman@isb-sib.ch>
> To: public-sparql-dev@w3.org<mailto:public-sparql-dev@w3.org>; public-rdf-dawg-comments@w3.org<mailto:public-rdf-dawg-comments@w3.org>; kidehen@openlinksw.com<mailto:kidehen@openlinksw.com>; bryan@systap.com<mailto:bryan@systap.com>
> Subject: Wishlist for SPARQL 1.2: Compatible query-hints, extra math operators
>
> Dear Workgroup, All,
>
> Maybe not the best moment to bring this up as the ink on SPARQL 1.1 is
> not even dry yet. But looking to the future could we start thinking
> about SPARQL 1.2 and what could be standardized there.
>
> The first need I am seeing is the need to standardize query hints.
>
> Oracle uses extra prefix declarations for query hints [1].
> BigData uses magic BGP's [2]
> Virtuoso introduced a new keyword ASSUME [3]
>
> The BigData and Virtuoso approach introduce query incompatibilities
> which is unfortunate. Oracle is ok in this respect as the unused
> prefixes won't affect any strictly compatible sparql engine. I like the
> idea that any SPARQL query will run on any store the only thing changing
> is speed. Extra keywords or non existing BGP's break this utopia :(
>
> The second is an expansion of the basic math operators to include at
> least (square)root. (square)root is very hard to implement using the
> current SPARQL constructs yet is a very useful function. (even if not exact)
>
> Regards,
> Jerven
>
>
>
> [1]
> http://docs.oracle.com/cd/E18283_01/appdev.112/e11828/sem_jena.htm#CBBIAGAF
> [2] http://sourceforge.net/apps/mediawiki/bigdata/index.php?title=QueryHints
> [3]
> http://sourceforge.net/mailarchive/forum.php?thread_name=51F67BB8.7030302%40openlinksw.com&forum_name=virtuoso-users
>
>
>
>
> --
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> Jerven Bolleman Jerven.Bolleman@isb-sib.ch<mailto:Jerven.Bolleman@isb-sib.ch>
> SIB Swiss Institute of Bioinformatics Tel: +41 (0)22 379 58 85
> CMU, rue Michel Servet 1 Fax: +41 (0)22 379 58 58
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