Re: on the turtle serialization of SHACL

On 14 Dec 2016, at 15:47, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
> 
> 
> 
> On 12/13/2016 07:15 PM, Holger Knublauch wrote:
>> Following linked data principles, every well-designed RDF vocabulary should
>> have a machine-readable RDF graph at the web server of its namespace. The
>> SHACL TTL file plays that role and will be uploaded to the W3C server at some
>> stage. That's its main role. 
> 
> Has W3C committed to hosting this document?  Has the W3C team been asked to
> determine whether W3C is doing this sort of thing at all?

The W3 hosts Turtle files for all it’s ontology standards, for example here’s Prov-O:

> Abstract
> 
> The PROV Ontology (PROV-O) expresses the PROV Data Model [PROV-DM] using the OWL2 Web Ontology Language (OWL2) [OWL2-OVERVIEW]. It provides a set of classes, properties, and restrictions that can be used to represent and interchange provenance information generated in different systems and under different contexts. It can also be specialized to create new classes and properties to model provenance information for different applications and domains. The PROV Document Overview describes the overall state of PROV, and should be read before other PROV documents.
> 
> The namespace for all PROV-O terms is http://www.w3.org/ns/prov#.
> 
> The OWL encoding of the PROV Ontology is available *here*.
> 


and the “here” links to a downloadble Turtle file. So, this requirement is common in the W3C - not a problem at all :-)

Cheers,
David




> 
>> Whether the word "normative" is the right term I
>> cannot say, 
> 
> Someone in the working group should determine whether "normative" is the right
> term.
> 
>> so I have avoided this term for now:
>> 
>> https://github.com/w3c/data-shapes/commit/376aeaac562bf824943a383904728a06f19f88c6
> 
> Has the working group signed of on this substantive change to SHACL?
> 
>> Nowhere in the document we state that this file needs to be imported into a
>> shapes graph, so it could not ever have fulfilled any other normative role
>> anyway.
> 
> I don't think that this is the case.  Even if this document is not imported,
> it was a normative document so whatever it says was part of SHACL.  So if this
> document contains sh:Shape rdfs:subClassOf sh:PropertyConstraint then it
> saying that throughout SHACL there is always a subclass relationship from
> shapes to property constraints so all shapes were property constraints in SHACL.
> 
>> I am surprised you don't see any utility in referring to this document at all.
>> Just a few days ago a colleague of mine asked me about this very file because
>> he wanted to understand the metamodel better. Such files are often a very
>> helpful way to learn RDF models, e.g. by browsing them with an RDF editing
>> tool. Furthermore, the RDF file can serve as backbone of a SHACL engine
>> implementation, and we use this very file in production in our SHACL engine on
>> a daily basis. So it is receiving quite a bit of testing along the way.
> 
> Yes, I can see that an RDF document about the SHACL vocabulary can have
> tutorial utility.  However then the document has to reflect the actual
> situation with respect to the SHACL vocabulary.  This does not appear to be
> the case.  There are lots of occurrences of rdfs:domain and rdfs:range in the
> document.  As SHACL doesn't do RDFS reasoning these are only creating false
> impressions.
> 
> As far as SHACL implementations depending on a document served by W3C, I think
> that the W3C team should sign off on that.
> 
>> 
>> FWIW, the general topic had been discussed at length before, see
>> https://www.w3.org/2014/data-shapes/track/issues/87
>> 
>> Holger
>> 
>> 
>> On 14/12/2016 11:17, Peter F. Patel-Schneider wrote:
>>> If the spec overrules the Turtle document, then I don't see how the Turtle
>>> document can be considered to be normative and I don't even see any utility in
>>> referring to the document at all.
>>> 
>>> However, I don't think that that is what you are saying.   You appear to be
>>> saying that if this document contains something like
>>> sh:Shape rdfs:subClassOf sh:PropertyConstraint .
>>> then even if this is not stated anywhere in the SHACL document every shape is
>>> also a property constraint in SHACL and all SHACL processors MUST treat them
>>> as such, i.e., all SHACL processors MUST signal a syntax error on shapes
>>> graphs like
>>> 
>>> se:s1 rdf:type sh:Shape ;
>>>  sh:targetNode ex:n1 ;
>>>  sh:class ex:c1 .
>>> 
>>> However only certain aspects of the Turtle document will have this kind of
>>> effect.  As you say, rdfs:domain and rdfs:range portions won't do anything.
>>> How then are they normative?
>>> 
>>> Further, it is the document itself that is being stated to be normative.  If
>>> changing namespace prefixes doesn't change anything then it seems to be more
>>> that the intent is not that the document is normative but that some RDF graph
>>> has some normative intent.
>>> 
>>> So:
>>> 
>>> ISSUE:  The intent and effects of the Turtle document are unclear.
>>> 
>>> 
>>> peter
>>> 
>>> 
>>> 
>>> 
>>> On 12/13/2016 04:32 PM, Holger Knublauch wrote:
>>>> The idea is that the existing TTL file is consistent with what is written in
>>>> the main spec. If there are errors, I welcome bug reports. If we are unsure,
>>>> we could add a statement along the lines of "the spec wins if the TTL file
>>>> contradicts".
>>>> 
>>>> But overall this TTL file has a similar impact as any other file that may be
>>>> imported into a shapes graph. So if someone adds a triple that makes
>>>> sh:PropertyConstraint rdfs:subClassOf sh:Shape, and SHACL is defined to look
>>>> for all SHACL instances of sh:Shape, then an engine will also treat those
>>>> property constraints as shapes. SHACL doesn't do RDFS inferencing, so
>>>> rdfs:domain has no impact unless the shapes graph has RDFS activated (which is
>>>> outside of SHACL's concern). Changing namespace prefixes has no impact on
>>>> behavior, changing sh:prefix triples would.
>>>> 
>>>> Holger
>>>> 
>>>> 
>>>> On 14/12/2016 9:50, Peter F. Patel-Schneider wrote:
>>>>> The current version of the SHACL document contains "The Turtle serialization
>>>>> of the SHACL vocabulary is part of the normative specification. However, the
>>>>> values of rdfs:label and rdfs:comment in that file are not normative.",
>>>>> pointing to a Turtle document available on the web.
>>>>> 
>>>>> In what sense is this document normative?
>>>>> 
>>>>> Would removing the line "rdfs:subClassOf sh:Constraint ;" from the part of
>>>>> the document about sh:Shape change anything about SHACL?  Would adding
>>>>> "sh:PropertyConstraint rdfs:subClassOf sh:Shape." somewhere to the document
>>>>> change anything about SHACL?  Would removing "rdfs:domain sh:Shape ;" from
>>>>> the part of the document about sh:property change anything aobut SHACL?
>>>>> Would changing "owl:" to "rowl:" throughout the document change anything
>>>>> about SHACL?  Would changing the document in any way change SHACL?
>>>>> 
>>>>> 
>>>>> Peter F. Patel-Schneider
>>>>> Nuance Communications
>>>>> 
>>>> 
>> 
>> 
>

Received on Wednesday, 14 December 2016 16:49:47 UTC