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Re: type and instance and subclass in SHACL documents

From: Irene Polikoff <irene@topquadrant.com>
Date: Sat, 12 Mar 2016 17:08:45 -0500
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
CC: <kcoyle@kcoyle.net>, <public-data-shapes-wg@w3.org>
Message-ID: <D309F994.95C2E%irene@topquadrant.com>

Peter,

Repeating that "SHACL instance is indeed very different from RDFS
instance¡± doesn¡¯t move the conversation forward. The question was ¡°why and
how¡± and you have not answered this question in a way that I could
understand.

Since no one else in the working group jumped in to answer this question
and, on contrary, several people joined me in asking it, I have to
conclude that no one else understand this either. If I am wrong, and there
is someone other than Peter who does, please, answer it. If something is
indeed very different from another thing, such difference should be
apparent to most group members.

As I recall, this topic has been brought up by Peter on and off during (at
least) the last 12 months. Realistically and practically speaking, if no
one else in the working group that is made of experts and experienced
practitioners understands this difference, even after a year of
discussions, I see this topic as having absolutely no practical relevance.
The chance that the broader community would understand it or care to
understand it or be impacted by it in any way whatsoever is infinitely
close to zero. 

I would venture even further and say that such unwavering focus on obscure
points that make no practical difference is they key obstacle to adoption
of RDF technology. As a community, we must overcome this tendency in order
to move forward.

Irene 




On 3/12/16, 4:30 PM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
wrote:

>The SHACL documents talk about instance.  If this is RDFS instance, then,
>yes,
>SHACL engines would always have to treat rdfs:label as an instance of
>rdf:Property.
>
>This is why I say that the SHACL documents should be very clear every time
>that they talk about instance that it is not the common RDFS instance that
>they are talking about but some new notion particular to SHACL,
>particularly
>as SHACL uses RDFS vocabulary.
>
>SHACL instance is indeed very different from RDFS instance.
>
>peter
>
>
>On 03/12/2016 10:05 AM, Irene Polikoff wrote:
>> We need rdf:type to know if something is an instance of a class (note
>>that I am saying simply 'instance' because I do not see the difference).
>> 
>> If {rdfs:label rdf:type rdf:Property} triple was provided to a SHACL
>>engine, then the violation would be raised.
>> 
>> How else could it be known from the data graph that rdfs:label is a
>>property? Or are you saying that SHACL engines should always include
>>triples in RDFS vocabulary when they do their processing?
>> 
>> Sent from my iPhone
>> 
>>> On Mar 11, 2016, at 10:36 PM, Peter F. Patel-Schneider
>>><pfpschneider@gmail.com> wrote:
>>>
>>> Using the RDFS definition of instance, rdfs:label is an instance of
>>> rdf:Property so it is in the scope of the shape and there is a
>>>violation.
>>> Using the SHACL definition of instance, rdfs:label is *not* an
>>>instance of
>>> rdf:Property so it is *not* in scope and there is *no* violation.
>>>
>>> peter
>>>
>>>
>>>> On 03/11/2016 04:50 PM, Karen Coyle wrote:
>>>> Peter, I admit that I, too, am having trouble understanding this.
>>>>(And so it
>>>> isn't all on Peter, if anyone else "gets it" maybe they could weight
>>>>in.) The
>>>> SHACL document uses the term "instance" 78 times. I admit I only
>>>>looked at the
>>>> first couple of dozen of those uses. For the most part they appear to
>>>>me to
>>>> conform to the RDFS definition of "instance" - meaning an instance of
>>>>class.
>>>> In some cases the term is used more colloquially, but those places in
>>>>the
>>>> document don't seem to be definitional.
>>>>
>>>> You say that it doesn't validate, but can you say what the difference
>>>>is in
>>>> the two definitions? I still see it as having to do with the
>>>>vocabulary
>>>> definition as opposed to the SHACL validation, but you didn't buy
>>>>that when I
>>>> suggested it. If I were to use a typical OWL-based validation,
>>>>rdfs:range
>>>> ex:label "range" would be flagged as inconsistent. The same would be
>>>>true if I
>>>> would have
>>>>  ex:someSubject dct:type "text" .
>>>> (dct:type has a range of rdf-schema#Class)
>>>>
>>>> If this isn't the issue, I would sure like to know what is.
>>>>
>>>> Thanks,
>>>> kc
>>>>
>>>>> On 3/11/16 2:22 PM, Peter F. Patel-Schneider wrote:
>>>>> The definition of SHACL depends on "instance".  This can be read to
>>>>>mean
>>>>> "RDFS instance" or "SHACL instance".  Under the former meaning the
>>>>>data graph
>>>>> does not validate against the shape.   Under the latter meaning the
>>>>>data graph
>>>>> does validate against the shape.
>>>>>
>>>>> peter
>>>>>
>>>>>
>>>>>> On 03/11/2016 02:15 PM, Irene Polikoff wrote:
>>>>>> I don©öt understand what you mean by
>>>>>>
>>>>>> "validates against this shape under SHACL instance but not under
>>>>>>RDFS
>>>>>> instance.©÷
>>>>>>
>>>>>> I am not able to parse the sentence.
>>>>>>
>>>>>> What are you doing? Taking a shape described and the graph
>>>>>>described and
>>>>>> running it against SHACL engine? What execution validates and what
>>>>>> execution doesn©öt validate?
>>>>>>
>>>>>>
>>>>>>
>>>>>> Irene
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 3/11/16, 5:03 PM, "Peter F. Patel-Schneider"
>>>>>><pfpschneider@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>>> On 03/11/2016 01:01 PM, Karen Coyle wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>> On 3/11/16 11:43 AM, Peter F. Patel-Schneider wrote:
>>>>>>>>> Consider the following shape (using obvious prefix declarations)
>>>>>>>>>
>>>>>>>>> sh:propertyShape a sh:Shape ;
>>>>>>>>>   sh:scopeClass rdf:Property ;
>>>>>>>>>   sh:property [ sh:predicate rdfs:label ;
>>>>>>>>>                 sh:minCount 1 ] .
>>>>>>>>>
>>>>>>>>> The data graph (using obvious prefix declarations)
>>>>>>>>>
>>>>>>>>> rdfs:range ex:label "range" .
>>>>>>>>>
>>>>>>>>> validates against this shape under SHACL instance but not under
>>>>>>>>>RDFS
>>>>>>>>> instance.
>>>>>>>>
>>>>>>>> Isn't this a problem with every vocabulary and not just RDFS? If
>>>>>>>>the
>>>>>>>> rules of
>>>>>>>> the vocabulary (such as domain and range) are not encoded as such
>>>>>>>>in
>>>>>>>> SHACL
>>>>>>>> then the SHACL result can be "in violation" of the vocabulary
>>>>>>>> definition.
>>>>>>>>
>>>>>>>> Now, if that is the case then I understand that violating the
>>>>>>>>foundation
>>>>>>>> vocabulary of RDF/RDFS may be more grave than violating a
>>>>>>>>user-developed
>>>>>>>> vocabulary, and in some cases doing the latter may indeed be the
>>>>>>>> intention of
>>>>>>>> the SHACL definition. So do we want to build into SHACL that it
>>>>>>>>must
>>>>>>>> follow
>>>>>>>> RDF/RDFS property and class definitions? And how feasible is that?
>>>>>>>>
>>>>>>>> kc
>>>>>>>
>>>>>>> This is only a real problem because SHACL uses "instance" in its
>>>>>>> specification, this term is also used centrally in RDFS, and SHACL
>>>>>>>uses
>>>>>>> RDFS
>>>>>>> vocabulary.
>>>>>>>
>>>>>>> The question then is how to read "instance" in SHACL
>>>>>>>documentation, i.e.,
>>>>>>> how
>>>>>>> to prevent readers of the SHACL documentation from seeing "RDFS
>>>>>>>instance"
>>>>>>> where "SHACL instance" is meant.
>>>>>>>
>>>>>>>
>>>>>>> peter
>>>
Received on Saturday, 12 March 2016 22:09:20 UTC

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