W3C home > Mailing lists > Public > public-data-shapes-wg@w3.org > March 2016

Re: shapes-ISSUE-134 (knowing inverse): does SHACL syntax distinguish inverse property constraints [SHACL Spec]

From: Holger Knublauch <holger@topquadrant.com>
Date: Fri, 11 Mar 2016 15:18:46 +1000
To: public-data-shapes-wg@w3.org
Message-ID: <56E25536.8010503@topquadrant.com>
Yes, we did not really investigate meta-shapes yet, and what the 
patterns of invalid shapes graphs are. This should be future work...

Holger


On 11/03/2016 15:16, Peter F. Patel-Schneider wrote:
> There isn't anything that currently says that the object of a sh:property
> triple can't be a sh:InversePropertyConstraint, i.e., this is a valid shapes
> graph currently.  It thus appears that this example would pass all inspections
> and then work incorrectly.
>
> As you say, making this syntactically illegal will solve this particular
> problem.  I do wonder if there are any other cases like this.  I just happened
> to notice this because of what you said about different code being needed for
> the different cases.
>
> peter
>
>
> On 03/10/2016 08:32 PM, Holger Knublauch wrote:
>> That would be a modeling error, i.e. an invalid shapes graph. The rules state
>> what the sh:defaultValueType is for sh:property and sh:inverseProperty.
>> However, the "range" of sh:property is limited to sh:PropertyConstraint only,
>> so it cannot have an sh:InversePropertyConstraint as values. If someone
>> creates such a situation then it would evaluate both. This case can easily be
>> checked using SHACL constraints at "compile time", reporting an error in the
>> shapes graph. We could also make sh:PropertyConstraint and
>> sh:InversePropertyConstraint disjoint...
>>
>> Holger
>>
>>
>> On 11/03/2016 14:22, Peter F. Patel-Schneider wrote:
>>> Oops, I messed up the example.  Sorry for the confusion.
>>>
>>> Here is what I meant
>>>
>>> ex:s a sh:Shape ;
>>>       sh:property _:c ;
>>>       sh:property [ sh:predicate ex:q ;
>>>                     sh:valueShape [ sh:inverseProperty _:c ] ] .
>>>
>>>    _:c [ sh:predicate ex:p ;
>>>           sh:minCount 5 ] .
>>>
>>> peter
>>>
>>>
>>>
>>> On 03/10/2016 08:12 PM, Holger Knublauch wrote:
>>>> On 11/03/2016 13:38, Peter F. Patel-Schneider wrote:
>>>>> _:c will be both a sh:PropertyConstraint and sh:InversePropertyConstraint.
>>>>> Which SPARQL query will it pick?  Both?  In this case things might work out,
>>>> Yes both. I am glad we agree.
>>> We don't agree, even here.  Doing both works only because _:c was used in the
>>> same place.
>>>
>>>>> but what happens if the incoming links are from different places, as in
>>>>>
>>>>> ex:s a sh:Shape ;
>>>>>      sh:property _:c ;
>>>>>      sh:property [ sh:predicate ex:q ;
>>>>>                    sh:valueShape [ sh:property _:c ] ] .
>>>>>
>>>>> _:c [ sh:predicate ex:p ;
>>>>>          sh:minCount 5 ] .
>>>> I see no problem there. In both cases it's a sh:PropertyConstraint based on
>>>> the sh:defaultValueType of sh:property. They are not executed at the same
>>>> time, and on different focus nodes.
>>>>
>>>> Does this answer your ticket?
>>>>
>>>> Holger
>>>>
>>>>
>>>>> peter
>>>>>
>>>>>
>>>>>
>>>>> On 03/10/2016 04:43 PM, Holger Knublauch wrote:
>>>>>> In the current draft this is handled by sh:defaultValueType:
>>>>>>
>>>>>> ex:s a sh:Shape ;
>>>>>>      sh:property _:c ;
>>>>>>      sh:inverseProperty _:c .
>>>>>> _:c [ sh:predicate ex:p ;
>>>>>>          sh:minCount 5 ] .
>>>>>>
>>>>>>
>>>>>> The engine will "add" two type triples:
>>>>>>
>>>>>> _:c a sh:PropertyConstraint .
>>>>>> _:c a sh:InversePropertyConstraint .
>>>>>>
>>>>>> The engine can then pick the correct validator (SPARQL query) for each
>>>>>> rdf:type of that constraint.
>>>>>>
>>>>>> Holger
>>>>>>
>>>>>>
>>>>>> On 11/03/2016 7:15, RDF Data Shapes Working Group Issue Tracker wrote:
>>>>>>> shapes-ISSUE-134 (knowing inverse): does SHACL syntax distinguish inverse
>>>>>>> property constraints [SHACL Spec]
>>>>>>>
>>>>>>> http://www.w3.org/2014/data-shapes/track/issues/134
>>>>>>>
>>>>>>> Raised by: Peter Patel-Schneider
>>>>>>> On product: SHACL Spec
>>>>>>>
>>>>>>>> From
>>>>>>> https://lists.w3.org/Archives/Public/public-data-shapes-wg/2016Mar/0106.html
>>>>>>>
>>>>>>>
>>>>>>> Some constraint types require different SPARQL queries (or JavaScript or
>>>>>>> whatever) depending on the direction of a property (or even worse, for an
>>>>>>> arbitrary path). For example sh:minCount needs to count subjects versus
>>>>>>> objects.
>>>>>>>
>>>>>>> Is it possible to determine whether a sh:minCount constraint is an inverse
>>>>>>> or not?  Consider
>>>>>>>
>>>>>>> ex:s a sh:Shape ;
>>>>>>>       sh:property _:c ;
>>>>>>>       sh:inverseProperty _:c .
>>>>>>> _:c [ sh:predicate ex:p ;
>>>>>>>           sh:minCount 5 ] .
>>>>>>>
>>>>>>>
>>>>>>>
>>
Received on Friday, 11 March 2016 05:19:22 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 19:30:30 UTC