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on order of evaluation in SHACL vs SPARQL [was Re: Order of filters]

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Tue, 27 Sep 2016 15:20:37 -0700
To: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>, Holger Knublauch <holger@topquadrant.com>
Cc: "public-rdf-sha." <public-rdf-shapes@w3.org>
Message-ID: <2f1ede66-895f-2227-7424-81c73a44f66f@gmail.com>
SPARQL does not require a particular order of evaluation.

Requiring a particular order of evaluation in SHACL makes it likely that SHACL
shapes cannot be validated by simply transforming them to a single SPARQL query.

Peter F. Patel-Schneider
Nuance Communications

On 09/23/2016 04:45 AM, Dimitris Kontokostas wrote:
> From what I remember, 
> Peter suggested that we are able to switch the order of validation and
> filtering in case filtering is very expensive and perform the filtering on
> fewer focus nodes
> At that time, failure in the validation was not noted as a possible problem
> and I relaxed the order.
> Since this may introduce undesired results I think it is safer to force the
> order as suggested by Holger
> Best,
> Dimitris. 
> On Fri, Sep 23, 2016 at 7:09 AM, Holger Knublauch <holger@topquadrant.com
> <mailto:holger@topquadrant.com>> wrote:
>     On 23/09/2016 11:36, Peter F. Patel-Schneider wrote:
>             order of processing for filters
>             The discussion of how filters are processed appears to be
>             contradictory.
>         First there is: "SHACL validation engines MAY alter the order of the
>         depicted steps as long as the returned validation results are correct."
>         Later there is: "Filter shapes MUST be evaluated before validating the
>         associated shapes or constraints."
>                  Comment (HK): Yes, the first sentence is IMHO incorrect and I
>             have
>         taken it out
>         (https://github.com/w3c/data-shapes/commit/3777e8e80aec9f9c1ba1bbb0dfdfce2b2acb9a12
>         <https://github.com/w3c/data-shapes/commit/3777e8e80aec9f9c1ba1bbb0dfdfce2b2acb9a12>).
>         The problem is that if an engine does filtering after validation, it
>         may run
>         into a failure that is otherwise not reached. I don't remember why we
>         added
>         that statement in the first place, do you @Dimitris?
>                  Comment (DK): This was changed to address a comment from Peter on
>         March 7th and resulted in this commit
>         This appears to be two different responses.  What is the situation?
>     Dimitris is this something you could clarify? I don't remember the history
>     of that topic.
>     Thanks
>     Holger
> -- 
> Dimitris Kontokostas
> Department of Computer Science, University of Leipzig & DBpedia Association
> Projects: http://dbpedia.org, http://rdfunit.aksw.org, http://aligned-project.eu
> Homepage: http://aksw.org/DimitrisKontokostas
> Research Group: AKSW/KILT http://aksw.org/Groups/KILT
Received on Tuesday, 27 September 2016 22:21:12 UTC

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