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Re: ISSUE-65: type and instance and subclass in SHACL documents

From: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>
Date: Thu, 10 Mar 2016 09:22:37 +0200
Message-ID: <CA+u4+a05NZa=1pMjX4k0fOpzwULpLv=RG6Kq0+t2BxsbXw_4jg@mail.gmail.com>
To: Holger Knublauch <holger@topquadrant.com>
Cc: public-data-shapes-wg <public-data-shapes-wg@w3.org>
Peter may correct me if I am wrong but the problem comes from the relation
of rdf:type / rdfs:subClassOf* and the definition of  subClass &
subProperty in RDFS
if someone defines ex:subClassOf rdfs:subPropertyOf rdfs:subClassOf and
uses ex:subClassOf in his relations SHACL will not be able to identify
these relations.
This is more or less what the biggest part of section 1.1 is about.

I think removing it completely will create more confusion. I would suggest
to postpone this until we get close candidate rec and then see how this can
be shortened.

On Thu, Mar 10, 2016 at 7:47 AM, Holger Knublauch <holger@topquadrant.com>
wrote:

> I would also like to know the answer to Irene's questions. If not, then I
> believe we can basically delete the contentious section 1.1. All we need to
> state is that SHACL does not require full RDFS inferencing. Section 1.1 has
> already created a lot of noise
>
> https://twitter.com/tombaker/status/694516400497545216
> https://twitter.com/metazippy/status/659379807784992768
>
> I have filed this email under ISSUE-65 so that we don't forget about it.
>
> Holger
>
>
> On 8/03/2016 9:00, Irene Polikoff wrote:
>
>> rdfs:subClassOf is defined as follows:
>>
>> "The property rdfs:subClassOf is an instance of rdf:Property that is used
>> to state that all the instances of one class are instances of another.
>>                 A triple of the form:
>>
>>    C1 rdfs:subClassOf C2
>>
>> states that C1 is an instance of rdfs:Class, C2 is an instance of
>> rdfs:Class and C1 is a subclass of C2. The rdfs:subClassOf property is
>> transitive."
>>
>> This definition doesn¹t really require for any inferred triples to be
>> present.
>>
>>
>> Is there anything in SHACL¹s use of rdfs:subClassOf that is contradictory
>> to the above definition?
>>
>> The only wording close to the definition of the word ³instance² that I
>> found in the specs is:
>>
>> "The members of a class are known as instances of the class.²
>>
>>
>> Finally, rdf:type is described in the RDFS spec as
>>
>> "The rdf:type property may be used to state that a resource is an instance
>> of a class.²
>>
>> RDF specs don¹t talk about rdf:type.
>>
>>
>> Is there anything in SHACL¹s use of the word ³instance" or of rdf:type
>> that contradicts this definition? If so, what is it?
>>
>>
>>
>> Irene Polikoff
>>
>>
>>
>>
>>
>>
>> On 3/7/16, 5:36 PM, "Holger Knublauch"<holger@topquadrant.com>  wrote:
>>
>> On 8/03/2016 1:51, Peter F. Patel-Schneider wrote:
>>>
>>>> On 03/06/2016 08:46 PM, Holger Knublauch wrote:
>>>>
>>>>> Thanks for the feedback, Peter. I have tried to address it here:
>>>>>
>>>> [...]
>>>>
>>>> On 7/03/2016 6:59, Peter F. Patel-Schneider wrote:
>>>>>
>>>>>> General
>>>>>>
>>>>> [...]
>>>>
>>>> It is not sufficient to say in 1.1 that SHACL has unique versions of
>>>>>> types
>>>>>> and instances.  These notions are in very widespread use.  Each time
>>>>>> that
>>>>>> SHACL deviates from the common, accepted W3C practice it should be
>>>>>> called
>>>>>> out, e.g., "SHACL type" or "SHACL instance".
>>>>>>
>>>>> I hope this doesn't need to be repeated each time as this may render
>>>>> the
>>>>> document harder to read. Furthermore, the terms "SHACL type" and "SHACL
>>>>> instance" would first need to be formally defined too.
>>>>>
>>>>> Instead, I suggest we should define what "type", "instance" and
>>>>> "subclass"
>>>>> mean in the remainder of the document. I have put a corresponding
>>>>> terminology
>>>>> block at the end of section 1.1
>>>>>
>>>> This is inadequate.
>>>>
>>>> SHACL uses RDF graphs and RDFS vocabulary.  There are already
>>>> definitions of
>>>> type and instance and subclass that come from RDF and RDFS.  SHACL
>>>> needs to
>>>> differentiate its version of type and instance and subclass from these
>>>> dominant notions and this can only be reliably done by qualifying them
>>>> each
>>>> time they appear in formal SHACL documents.
>>>>
>>>> Alternatively the SHACL document could use different words for these
>>>> relationships or could restrict the inputs that it handles so that it
>>>> uses the
>>>> dominant versions of type and instance and subclass.
>>>>
>>> My interpretation of the situation is
>>>
>>> - RDF and RDFS define the IRIs of vocabulary terms rdf:type and
>>> rdfs:subClassOf
>>> - terms like subclass, type and instance already existed before RDFS and
>>> carry intuitive meaning
>>> - there is no need to over-complicate a situation that is already clear
>>> to most readers
>>>
>>> The only difference between our definitions of the terms is that you
>>> think that subclassing must always require inferences (domain, ranges
>>> etc). I believe these concepts are orthogonal. Some rdfs:subClassOf
>>> triples may be the result of inferencing, but it doesn't matter to SHACL
>>> where they came from. As long as we make this clear in the beginning, I
>>> hope we can keep the document intuitive and not over-complicate it.
>>>
>>> Holger
>>>
>>>
>>>
>
>


-- 
Dimitris Kontokostas
Department of Computer Science, University of Leipzig & DBpedia Association
Projects: http://dbpedia.org, http://rdfunit.aksw.org, http://
http://aligned-project.eu
Homepage:http://aksw.org/DimitrisKontokostas
Research Group: AKSW/KILT http://aksw.org/Groups/KILT
Received on Thursday, 10 March 2016 07:23:34 UTC

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