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Re: type and instance and subclass in SHACL documents

From: Karen Coyle <kcoyle@kcoyle.net>
Date: Fri, 11 Mar 2016 16:50:14 -0800
To: public-data-shapes-wg@w3.org
Message-ID: <56E367C6.4090103@kcoyle.net>
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.


On 3/11/16 2:22 PM, Peter F. Patel-Schneider wrote:
> The definition of SHACL depends on "instannce".  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 don¹t understand what you mean by
>> "validates against this shape under SHACL instance but not under RDFS
>> instance.²
>> 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 doesn¹t 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

Karen Coyle
kcoyle@kcoyle.net http://kcoyle.net
m: 1-510-435-8234
skype: kcoylenet/+1-510-984-3600
Received on Saturday, 12 March 2016 00:50:27 UTC

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