Re: graph containing comprehensive set of ill-formed shapes

Peter,

Merits aside, there is a strong procedural reason for not adding such requirement. As you know, the working group charter is coming to the end. W3C has a morrotorium on publishing new versions that is starting now and will last for at least a week, may be more. Then, after a document with a new requirement is published, the implementers would need to comply, etc. All of this pushes the timescale.

Further, you brought up the topic of checking validity of the shapes graph many times in the past, even raising a formal objection prior to the CR. I don’t believe you are providing any new information now.

Irene

> On Apr 22, 2017, at 3:58 PM, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
> 
> There is a very simple test to ensure that are not SHACL-SPARQL constructs in
> a shapes graph.  Just look for sh:sparql values in shapes and SHACL instances
> of sh:ConstraintComponent.  If there are none then the only effective
> constructs in the shapes graph are in SHACL Core.
> 
> Of course there are cases where a SHACL Core processor would otherwise produce
> the same results as a SHACL-SPARQL processor on a shapes graph, but I don't
> think that that is what is needed here.
> 
> As far as future versions of SHACL are concerned I don't see how there is any
> way to ensure that a SHACL Core processor (or a SHACL-SPARQL processor) for
> the current version of SHACL does the right thing for future versions of
> SHACL.  Future versions of SHACL could be written so that changes to
> SHACL-SPARQL did not require changes to SHACL Core implementations, of course.
> An easy way to achieve this under my proposal would be to have the future
> version of SHACL-SPARQL only make changes that are only effective if there are
> SHACL instances of sh:ConstraintComponent in the shapes graph.
> 
> 
> My proposal eliminates an important source of silent interoperability failures
> between SHACL Core and SHACL-SPARQL implementations.   It is much like C
> compilers complaining if they see C++ syntax, even if that syntax would not
> change the behaviour of the program.
> 
> My proposal is extremely simple to implement and its run-time costs are
> minimal.  I see no reason not to add it to SHACL.
> 
> 
> Peter F. Patel-Schneider
> Nuance Communications
> 
> 
> On 04/21/2017 10:45 PM, Dimitris Kontokostas wrote:
>> 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
>> <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto: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>
>>>>>>> 
>>>>> 
>>> 
>>

Received on Saturday, 22 April 2017 23:18:38 UTC