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Re: type and instance and subclass in SHACL documents

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Mon, 7 Mar 2016 15:00:03 -0800
To: Holger Knublauch <holger@topquadrant.com>, public-data-shapes-wg@w3.org
Message-ID: <56DE07F3.3040403@gmail.com>
On 03/07/2016 02:36 PM, Holger Knublauch 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

In some contexts yes.  Not in a context RDF graphs and rdfs:subClassOf are
present.  In this context, RDF and RDFS type, instance, and subclass are in
play so different meanings of these terms need to be called out explicitly.

> - there is no need to over-complicate a situation that is already clear to
> most readers

I don't see how it can be clear to readers if the document itself is incorrect
in places.

> The only difference between our definitions of the terms is that you think
> that subclassing must always require inferences (domain, ranges etc). 

Not just subclassing, but also typing and instance.   SHACL uses neither the
RDF nor the RDFS meaning of both these terms.

> 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.

Right now the document is hard to read.  I have to continually remind myself
that type, instance, and subclass have new meanings, to the point where I do
not catch places that are incorrect in the document.

> Holger

peter
Received on Monday, 7 March 2016 23:00:46 UTC

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