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Re: Order of filters

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Fri, 23 Sep 2016 10:31:47 -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: <88dc14b9-a03f-edb3-df88-02a1cc5bbc81@gmail.com>
There is great utility in not requiring an order of evaluation here.  It is
easy to specify which failures in constraints count - the ones for nodes that
pass all the filters. Given this, the order should not be mandated.

On the other hand, how filters themselves are evaluated is left unspecified
and different approaches can change whether a failure occurs.  This needs to
be addressed.


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 Friday, 23 September 2016 17:32:24 UTC

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