Re: Profiles in Linked Data

On 5/11/15 11:39 AM, Svensson, Lars wrote:
> John,
>
> On Friday, May 08, 2015 10:05 PM, John Walker wrote:
>
>> >Hi Lars
>> >
>>> > >On May 8, 2015 at 5:44 PM "Svensson, Lars"<L.Svensson@dnb.de>  wrote:
>>> > >
>>> > >
>>> > >John, Kingsley,
>>> > >
>>> > >I wrote:
>>>>>> > > >>>OK, I can understand that. Does that mean that if I have under the same
>> >URI
>>>>>> > > >>>serve different representations (e. g. rdf/xml, turtle and xhtml+RDFa) all
>> >those
>>>>>> > > >>>representations must return exactly the same triples, or would it be
>> >allowed to
>>>>>> > > >>>use schema.org in the RDFa, W3C Organisation Ontology for rdf/xml and
>> >foaf
>>>>>> > > >>>when returning turtle? After all it's different descriptions of the same
>> >resource.
>>> > >
>>> > >John wrote:
>>> > >
>>>>> > > >>My take on this is each representation (with negotiation only on format via
>>>>> > > >>HTTP Accept header)*should*  contain the same set of RDF statements
>>>>> > > >>(triples).
>>>>> > > >>Also one could define a different URL for each representation which can
>> >be
>>>>> > > >>linked to with Content-Location in the HTTP headers.
>>>>> > > >>
>>>>> > > >>We’re you to introduce an additional (orthogonal) way to negotiate a
>> >certain
>>>>> > > >>profile, this would be orthogonal to the format. Following on from above,
>> >one
>>>>> > > >>could then have a separate URL for each format-profile combination.
>>> > >
>>> > >Kingsley wrote:
>>> > >
>>>> > > >Yes.
>>>> > > >
>>>> > > >For the sake of additional clarity, how about speaking about documents and
>>>> > > >content-types rather than "representation" which does inevitably conflate
>> >key
>>>> > > >subtleties, in regards to RDF (Language, Notations, and Serialization
>> >Formats)?
>>> > >
>>> > >The terminology is fine with me, as long as we don't forget the entities we
>> >describe.
>>> > >
>>> > >So to repeat my question in another mail: I have an entity described by a
>> >(generic) URI. Then I have three groups of documents describing that entity, the
>> >first uses schema.org, the second group uses org ontology and the third uses
>> >foaf. All documents are available as RDF/XML, Turtle and xhtml+RDFa. How
>> >does a client that knows only the generic URI for the resource tell the server
>> >that it prefers foaf in turtle and what does the server answer?
>> >
>> >I believe that the two options are in HTTP headers or in the query string part of
>> >the URI. In the latter case I guess you would say that is no longer the generic
>> >URI.
>> >
>> >I note in the JSON-LD spec it is stated "A profile does not change the semantics
>> >of the resource representation when processed without profile knowledge, so
>> >that clients both with and without knowledge of a profiled resource can safely
>> >use the same representation", which would no longer hold true if the profile
>> >parameter were used to negotiate which vocabulary/shape is used.
> Yes, I noted that text in RFC 6906, too, but assumed that "unchanged semantics of the resource" meant that both representations still describe the same thing (which they do in my case). Would a change in description vocabulary really mean that I change the semantics of the description?
>
> If so, I'd be happy to call it not a "profile", but a "shape" instead (thus adopting the vocabulary of RDF data shapes).

Lars,

We have to be careful here. RDF Language sentences/statements have a 
defined syntax as per RDF Abstract Syntax i.e., 3-tuples organized in 
subject, predicate, object based structure. RDF Shapes (as far as I 
know) has nothing to do with the subject, predicate, object structural 
syntax of an RDF statement/sentence. Basically, it's supposed to provide 
a mechanism for constraining the entity type (class instances) of RDF 
statement's subject and object, when creating RDF statements/sentences 
in documents. Think of this as having more to do with what's regarded as 
data-entry validation and control, in other RDBMS quarters.

The function of the "profile" I believe you (and others that support 
this) are seeking has more to do with enabling clients and servers (that 
don't necessarily understand or care about RDF's implicit semantics) 
exchange hints about the nature of RDF document content (e.g., does it 
conform to Linked Data principles re. entity naming [denotation + 
connotation] ).

Cut long story short, a "profile" hint is about the nature of the RDF 
content (in regards to entity names and name interpretation), not its 
shape (which is defined by RDF syntax).

-- 
Regards,

Kingsley Idehen 
Founder & CEO
OpenLink Software
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