Re: graph containing comprehensive set of ill-formed shapes

Hi Peter,

Although I agree that interoperability is important, I don't think it is
realistic to require shacl core processor to be able to detect shacl sparql
constructs without implementing (part of) shacl sparql.

For example, a constraint component could be defined but never used in a
shapes graph.

Also, what about deactivated shapes, shapes that are never reached in a
validation or ill formed constructs?

This easily becomes more complex than identifying two graph patterns

In addition, it is not future proof. What if we later define shacl sparql+
or another variant? Will all preexisting shacl core implementations break
for not detecting the new constructs?

An informative note about interoperability would helpful but conformance
criteria are hard to define imho.

Best,
Dimitris

Typed by thumb. Please forgive brevity, errors.

On Apr 22, 2017 4:09 AM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
wrote:

> Note that SHACL implementations that ignore SHACL-SPARQL constructs can
> produce more violations than even a SHACL implementation that is in
> complete
> compliance with all the SHACL constructs.   There are very simple examples
> that demonstrate this, such as
>
>   ex:s1 a sh:NodeShape ;
>    sh:targetNode ex:i ;
>    sh:not [ sh:sparql "SELECT $this WHERE { }" ] .
>
> peter
>
>
> On 04/21/2017 04:03 PM, Irene Polikoff wrote:
> > Peter,
> >
> > We will discuss this at the next WG meeting.
> >
> >
> >> On Apr 21, 2017, at 5:30 PM, Peter F. Patel-Schneider <
> pfpschneider@gmail.com> wrote:
> >>
> >> The situation with respect to RDFS/OWL is quite different from that for
> SHACL.
> >> For starters, RDFS and OWL are two different recommendations, so there
> is some
> >> expectation that there might be differences between them.  On the other
> hand
> >> SHACL is one recommendation so there should be an expectation of
> >> interoperability between different SHACL implementations, even between
> SHACL
> >> Core and SHACL-SPARQL.
> >>
> >> Further, there is a useful interoperability between RDFS and OWL - RDFS
> >> entailment is sound with respect to OWL entailment (subject to some
> annoying
> >> caveats).  The same can't be said for SHACL Core versus SHACL-SPARQL  In
> >> general the violations reported by SHACL Core implementations will be
> >> different from those reported by SHACL-SPARQL implementations - some
> >> violations will be reported only by SHACL Core implementations and other
> >> violations will be reported only by SHACL-SPARQL implementations.  These
> >> differences may only arise long after deployment.
> >>
> >> Fortunately there is a simple change that alleviates much of this
> >> interoperability problem.  Just require that SHACL implementations at
> least
> >> have a mode where they signal when they see constructs that they do not
> >> handle.  This is already a requirement for sh:entailment so it is not
> as if
> >> requirements for signalling unhandled constructs is alien to SHACL.
> With this
> >> simple change users can ensure that they will be quickly notified if
> there is
> >> a chance of interoperability failures.
> >>
> >> A sound method for detecting the potential use of SHACL-SPARQL
> construct in
> >> shapes is very simple - it is not necessary to process SPARQL-based
> constraint
> >> components to find their parameters.  All that is needed is to check
> for the
> >> absence of sh:sparql constructs in shapes and the absence of SHACL
> instances
> >> of sh:ConstraintComponent in the shapes graph.  This easy method will
> produce
> >> a signal in cases where a SHACL-based constraint component is present
> but
> >> unused - certainly not a significant problem and probably not a problem
> at all.
> >>
> >> So there is a very easy method to make SHACL Core and SHACL-SPARQL
> >> implementations much more interoperable.  Given that one of the tenets
> of W3C
> >> recommendations is interoperability this method needs to be required
> for SHACL
> >> implementations.
> >>
> >> Peter F. Patel-Schneider
> >> Nuance Communications
> >>
> >>
> >> On 04/21/2017 12:47 PM, Irene Polikoff wrote:
> >>> I don’t think I follow.
> >>>
> >>> Two SHACL Core processors will not produce different results. They
> will both only understand SHACL Core and produce results for the shapes
> “inside” SHACL Core.
> >>>
> >>> SHACL SPARQL constructs are valid RDF, but SHACL Core processors do
> not understand or interpret their semantics.
> >>>
> >>> Similarly, to how an RDFS inference engine will ignore OWL
> restrictions - they don’t mean anything special to it. And an OWL
> inferencing engine that only supports one profile (let’s say OWL RL) will
> not be signaling that there are some axioms which meaning it didn’t
> interpret.
> >>>
> >>>> On Apr 21, 2017, at 3:03 PM, Peter F. Patel-Schneider <
> pfpschneider@gmail.com> wrote:
> >>>>
> >>>> It is important for interoperability that SHACL Core implementations
> are
> >>>> required to *not* silently produce different results on valid shapes
> graphs.
> >>>> Instead they must be required to signal that they have been given a
> shapes
> >>>> graph that they do not completely handle.
> >>>>
> >>>> peter
> >>>>
> >>>>
> >>>> On 04/21/2017 12:01 PM, Irene Polikoff wrote:
> >>>>> But, of course, SHACL Core and SHACL-SPARQL implementations will
> produce different results. This is by design.
> >>>>>
> >>>>> SHACL Core processors do not support SHACL-SPARQL. By definition, a
> SHACL Core and a SHACL SPARQL processors are only interoperable for a
> subset of SHACL which is SHACL Core and sh:sparql is not in SHACL Core.
> >>>>>
> >>>>>> On Apr 21, 2017, at 2:43 PM, Peter F. Patel-Schneider <
> pfpschneider@gmail.com> wrote:
> >>>>>>
> >>>>>> A SHACL implementation that silently ignores sh:sparql constructs
> produces an
> >>>>>> interoperability nightmare.
> >>>>>>
> >>>>>> For example, such an implementation will produce no violations for
> the shape
> >>>>>> ex:sparql a sh:NodeShape ;
> >>>>>>  sh:targetNode ex:i ;
> >>>>>>  sh:sparql "SELECT ?this WHERE { }" .
> >>>>>> A SHACL-SPARQL implementation will instead produce a violation.
> >>>>>>
> >>>>>> peter
> >>>>>>
> >>>>>>
> >>>>>> On 04/21/2017 03:39 AM, Irene Polikoff wrote:
> >>>>>>> Peter,
> >>>>>>>
> >>>>>>> If your implementation is SHACL Core only, how could SHACL-SPARQL
> constructs affect it? It would seem to me that the values in the sh:spraql
> triples would be no different to it than values in the ex:foo (or any user
> defined predicate) triples.
> >>>>>>>
> >>>>>>> Sent from my iPhone
> >>>>>>>
> >>>>>>>> On Apr 21, 2017, at 12:45 AM, Peter F. Patel-Schneider <
> pfpschneider@gmail.com> wrote:
> >>>>>>>>
> >>>>>>>> My alt-SHACL implementation does complete syntax checking,
> signalling whenever
> >>>>>>>> in encounters a shape or path or list that is not correctly
> formed.  My
> >>>>>>>> implementation has a strict mode that signals whenever the
> putative shapes
> >>>>>>>> graph contains anything that violates any of the SHACL Core
> syntax rules or
> >>>>>>>> contains a recursive shape or contains SHACL-SPARQL constructs
> that could
> >>>>>>>> affect validation.  To test this checking I had put together an
> RDF graph
> >>>>>>>> containing a comprehensive set of constructs that need to be
> checked.
> >>>>>>>>
> >>>>>>>> I just updated this graph, and the associated checking code, to
> incorporate
> >>>>>>>> the numerous additional syntax rules that were added when the
> SHACL document
> >>>>>>>> became a candidate recommendation.   I include the graph here.
> It can be
> >>>>>>>> turned into a comprehensive set of syntax test cases for SHACL
> Core by just
> >>>>>>>> separating it into small graphs each containing one of the test
> shapes.
> >>>>>>>>
> >>>>>>>> The amount of code required to do complete syntax checking was
> quite modest.
> >>>>>>>> Running my implementation over the graph was helpful in finding
> bugs such as
> >>>>>>>> incorrect recursion checks in the path code.  I strongly
> recommend that every
> >>>>>>>> SHACL implementation be run on every shape in this graph.
> >>>>>>>>
> >>>>>>>> Peter F. Patel-Schneider
> >>>>>>>> Nuance Communications
> >>>>>>>> <syntax.ttl>
> >>>>>
> >>>
> >
>
>