Re: Issue-185 filter execution ordering

If we take SPARQL generation as an argument, then shouldn't we extend 
this to targets, too? Typically an engine would generate a SPARQL query 
that includes the target binding clause in the beginning, then applies 
the filters and then the constraints. But of course, an optimizer may 
reorder these pieces.

So in a sense, your argument that keeping the order undefined is 
consistent with the rest of SHACL is not really valid, because we assume 
that targets are selected first, before filters and constraints - they 
produce the pre-bindings for ?this. And even if we hypothetically 
deleted filter shapes, we would still have the same questions with targets.

Holger


On 10/11/2016 15:20, Dimitris Kontokostas wrote:
> Hi Marq,  thanks for the pull request
> https://github.com/w3c/data-shapes/pull/23 
> <https://github.com/w3c/data-shapes/pull/23>
>
> Since you were one of the main people pushing to enforce ordering 
> during the call (with Ted) I am trying to see what use cases you are 
> trying to cover with this change.
>
> The way I see it it is like this, but maybe I am missing something
>
> A) with ordering
>  - there is NO room for engine optimisations
>  - we avoid some strange / rare situations when fatal errors occur.
>
> but fatal errors are a) implementation specific and b) from my 
> experience come  from badly written / malformed SPARQL queries (in 
> SPARQL-based systems).
>
> going further into fatal errors and execution ordering, we have the 
> exact same issue for sh:and and sh:or
> where we decided to allow the engines to choose the execution ordering 
> despite the fact that fatal errors may change the results
>
> https://www.w3.org/2014/data-shapes/track/issues/76
> https://www.w3.org/2015/08/20-shapes-minutes.html#resolution04
>
>
> B) without dictating execution ordering
>  - it is consistent with the existing design of SHACL
>  - We allow the engine to decide what is the best way to the processing
>  - we can fit all filters / shape constraints into a single SPARQL query
>
> I see consistency and two use cases in (B), what can you achieve with (A)?
>
> Best,
> Dimitris
> -- 
> 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 
> <http://aksw.org/DimitrisKontokostas>
> Research Group: AKSW/KILT http://aksw.org/Groups/KILT 
> <http://aksw.org/Groups/KILT>
>