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Re: SHACL recursion based on SPARQL (idea)

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 3 Mar 2016 11:17:06 -0800
To: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>, public-data-shapes-wg <public-data-shapes-wg@w3.org>
Message-ID: <56D88DB2.6090307@gmail.com>
It looks to me as if this is a way to determine what to run the shapes on in a
bottom-up implementation.  However, it does not appear to address how to
determine results when recursion happens, at least as far as I can see, and
that is the issue that needs to be addressed for SHACL in general.

For example, how does this approach address whether there is a violation in

ex:a rdf:type ex:Person ;
     p1 ex:o1 .
ex:o1 p2 ex:o2 .
ex:o2 p3 ex:o3 .
ex:o3 p1 ex:o1 .


On 03/02/2016 11:54 PM, Dimitris Kontokostas wrote:
> I maybe surprising to the group that I make such a proposal :) but had a
> (crazy) idea about enabling *some* recursion on shacl that is consistent with
> the rest of the spec and is based in SPARQL.
> The basic idea is to use implicit scopes and property paths to achieve that goal. 
> (Note that I have not yet implemented this, this is just a draft idea and
> wanted to see if you would like to explore more on this)
> Example:
> ShpA (scopeClass ex:Person, property(p1, valueShape: ShpB))
> ShpB ( property (p2, isIRI, (valueShape: ShpC))
> ShpC ( property (p3, isIRI, (valueShape: ShpA))
> In this approach, every shape may have an explicit scope (such as scopeClass,
> scopeNode, etc) as well as implicit scopes that derive from sh:valuShape.
> to identify the implicit scope of a shape we traverse all the current shape
> references to that shape from other shapes and give them implicit scopes only
> if the other shapes have an explicit scope.
> An example with make it easier to understand
> (note that this is without recursion and is  how RDFUnit has currently
> implemented sh:valueShape)
> ShpA has an explicit scope with scopeClass ex:Person (we do not take ShpC into
> account here)
> ShpB has no explicit scope and 1 implicit scope: [a ex:Person] / p1
> ShpC has no explicit scope and 1 implicit scope: [a ex:Person] / p1 / p2
> note that ShpC gets an implicit scope from ShpA only as ShpB has no explicit
> scope, if it did, we would add an extra scope
> to put this in SPARQL, ShpC would have the following scope
> select ?this where { [] a ex:Person ; p1/p2 ?this }
> if we want to add recursion into this what we could do is something like the
> following
> ShpA has an explicit scope with scopeClass [ a ex:Person]  and 1 implicit
> scope [a ex:Person] / (p1 / p2 / p3 )+
> ShpB has no explicit scope and 1 implicit scope: [a ex:Person] / (p1 / p2 / p3
> )* / p1
> ShpC has no explicit scope and 1 implicit scope: [a ex:Person] / (p1 / p2 / p3
> )* / p1 / p2
> As I said, this is just a draft idea for very simple recursion in simple shape
> definitions.
> I have not yet tested it or thought how this will behave in nested AND / OR (I
> think NOT is out of the question anyway), I just wanted to share this and get
> you feedback if it is worth exploring more
> Best
> Dimitris
> -- 
> Dimitris Kontokostas
> Department of Computer Science, University of Leipzig & DBpedia Association
> Projects: http://dbpedia.org, http://rdfunit.aksw.org,
> http://http://aligned-project.eu <http://aligned-project.eu/>
> Homepage:http://aksw.org/DimitrisKontokostas
> Research Group: AKSW/KILT http://aksw.org/Groups/KILT
Received on Thursday, 3 March 2016 19:17:45 UTC

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