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Re: More specific proposal on the vocabulary expansion (a.k.a. vocab proxy) feature

From: Gregg Kellogg <gregg@kellogg-assoc.com>
Date: Thu, 4 Aug 2011 14:10:19 -0400
To: Ivan Herman <ivan@w3.org>
CC: W3C RDFWA WG <public-rdfa-wg@w3.org>
Message-ID: <ACF6C6E2-67FC-4D03-B41C-71EE954845C2@kellogg-assoc.com>
Ivan, we actually created a GitHub repository for this as a member submission: https://github.com/rdfa/ms-proxy-vocab. This might be a good place to add this text, along with the motivation. (It was on my list of things to do, thanks for jumping on this).

More below:
On Aug 4, 2011, at 9:33 AM, Ivan Herman wrote:

> Guys,
> 
> I have had a long discussion with Manu today, and we both agreed that, in view of all the issues surrounding RDFa and its future, it would be good to 'spec' the proxy feature as soon as possible to move ahead. I had a very first stab at it, which is clearly not spec quality but at least gathers my thoughts on how this thing could be specified relatively quickly and succinctly. My goal was to try to minimize what *we* should specify and, rather, rely on existing specifications. We may want to check that with some people who are good at semantics.
> 
> Here it is.
> 
> Cheers
> 
> Ivan
> 
> 
> [[[
> <h1>RDFa Vocabulary Expansion</h1>
> 
> Once the default graph is generated following the processing steps defined at @@LINK@@, RDFa processors MAY (or SHOULD?) perform the following processing steps on the default graph.
> 
> - For all URI-s that appear as a value of a @vocab attribute in the RDFa source, that URI is dereferenced. If the dereferencing yields the serialization of an RDF graph, that graph is merged with the default graph. (RDFa processor MUST accept an RDF graph serialized in RDFa, SHOULD accept an RDF graph serialized in RDF/XML[REF] or Turtle[REF], and MAY accept other serialization formats of RDF.)

Need to guard against recursion here. At least to abort an attempt to import a graph that is already in the process of, or has already been imported.

> - The processor expands the default graph using the RDFa Vocab Entailment @@@Link to section below@@@.
> 
> <h2>RDFa Vocab Entailment</h2>
> 
> <h3>RDFa Vocab Entailment definition (normative)</h3>
> 
> For the purpose of vocabulary processing, RDFa uses restricted version of the full RDFS entailment[1]. This entailment is based on a restriction of the vocabulary used by the RDFS Interpretation[2]. Indeed, the RDFa vocab entailment vocabulary contains only the following terms:
> 
> - rdf:type rdfs:subClassOf rdfs:subPropertyOf
> 
> and the RDFa vocabulary entailment does not use any of the axiomatic triples defined in [2] or [3].

We had also discussed that datatype coercion would be something that a proxy vocabulary might accomplish, however, as I mentioned, I don't think this can be done through normal entailment regimes. It's also a theme in recent Microdata-RDF discussions [5] which have a similar issue. @itemvaltype is not universally loved, and it's questionable how much @datatype is used properly in RDFa. Clearly, being able to use some combination of rdfs:range and lexical value space could be useful in reproducing this, but it would seem to need to be done at processing time, not after the fact.

If we could solve this issue, it would be useful across all RDF serializations where publishers are often lazy about using typed literals.

> <h3>RDFa Vocab Entailment Rules (informative)</h3>
> 
> While the formal definition of the RDFa Entailment is defined in terms of RDF Semantics, practical implementations may rely on the (informative) entailement rules published in the RDF Semantics documents[4]. In particular, the relevant rules are (using the rule identification in [4]): rdfs5, rdfs7, rdfs9, and rdfs11.  
> 
> <h2>Vocabulary Expansion Contol of RDFa Processors</h2>
> 
> Comforming RDFa processors are <em>not</em> required to provide vocabulary expansion. 
> 
> If an RDFa processor provides vocabulary expansion, it MUST NOT be done by default. Instead, the processor must provide an option, <tt>vocab_expansion</tt>, which, when used, instructs the RDFa processor to perform a vocabulary expansion before returning the default graph.
> 
> 
> [1] http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#rdfs_entailment
> [2] http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#rdfs_interp
> [3] http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#InterpVocab
> [4] http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#rules
> ]]]
> 
> 
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> PGP Key: http://www.ivan-herman.net/pgpkey.html
> FOAF: http://www.ivan-herman.net/foaf.rdf

Gregg

[5] https://plus.google.com/112095156983892490612/posts/aUqGQSLzDPv
Received on Thursday, 4 August 2011 18:11:15 UTC

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