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Re: Another way other than @profile, @vocab or @map

From: Ivan Herman <ivan@w3.org>
Date: Mon, 22 Mar 2010 06:38:26 -0400
Message-ID: <4BA748A2.6020702@w3.org>
To: Toby Inkster <tai@g5n.co.uk>
CC: RDFa WG <public-rdfa-wg@w3.org>

re the RDFS processing, I have several problems with this

- implementing RDFS is not complicated but is not easy either. If a
processor wants to implement the full RDFS entailment, then care should
be taken about the potential infinity brought in by axiomatic triples
and rdf:_i type triples, for example. I realize that your proposal does
not need a full RDFS entailment, but then we end up defining a specific
entailment regime for RDFa, and specing that properly is not that easy

- regardless of the difficulty of implementation, I myself regard RDFa,
from the SW point of view, as yet another standard serialization of RDF.
But, with an RDFS processing in the picture, that is not true any more.
This is a major step to take...

- One of the issues we have with the current RDFa is its relative
complexity for authors. This is the whole discussions we are having,
after all, and this was the main incentive for the creation of
microdata. I believe that, whatever we end up doing, the result of this
discussion should be a significant step toward authors and
simplification. An average HTML author will not understand and, frankly,
will not want to understand what RDFS processing is. Introducing RDFS
processing into the picture could backfire and alienate HTML authors in
my view

- Finally, I am not sure what it solves. One of the central issues we
have is whether there is a reference to an external file or not in
processing the RDFa content, and your proposal seems to rely on that...

Sorry, but we seem to disagree on this:-(



On 2010-3-20 18:43 , Toby Inkster wrote:
> On Fri, 2010-03-19 at 22:05 -0400, Manu Sporny wrote:
>> Mark's UK consultation work is one use case that demonstrates[1] that
>> mixing vocabularies to create RDFa Profiles/Argots are helpful. [...]
>> Digital Bazaar (my company) would like to mix the Music Ontology with
>> the Good Relations Ontology in a way that bloggers could express music
>> for purchase without having to invent a new vocabulary, and making it
>> as easy to use (correctly) as a Microformat[3]. 
> These are laudable goals, but in my mind not enough to justify the RDFa
> profiles approach. There's more than one way to do this.
> Let's take a simple case of mixing two well known RDF vocabularies: FOAF
> and Dublin Core. We wish to note that a foaf:Document has a dc:title.
> In RDFa 1.0, this might be:
> 	<html xmlns="http://www.w3.org/1999/xhtml"
> 	      xmlns:dc="http://purl.org/dc/terms/"
> 	      xmlns:foaf="http://xmlns.com/foaf/0.1/"
> 	      xml:lang="en">
> 	  <head typeof="foaf:Document">
> 	    <title property="dc:title">Foo</title>
> 	  </head>
> 	  ...
> 	</html>
> So, how could we allow these terms from different vocabularies to be
> used in RDFa 1.1 without as much fuss? Firstly, we define a mechanism
> for setting a default prefix - I'll use the attribute @vocab in this
> example:
> 	<html xmlns="http://www.w3.org/1999/xhtml"
> 	      vocab="http://example.com/my-vocab#"
> 	      xml:lang="en">
> 	  <head typeof="Document">
> 	    <title property="title">Foo</title>
> 	  </head>
> 	</html>
> So what have we achieved? We end up with these two triples:
> 	<>
> 	  <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
> 	    <http://example.com/my-vocab#Document> .
> 	<>
> 	  <http://example.com/my-vocab#title>
> 	    "Foo"@en .
> Not quite what we wanted, but still... suppose the vocab document at
> <http://example.com/my-vocab> contains the following triples:
> 	<http://example.com/my-vocab#Document>
> 	  <http://www.w3.org/2000/01/rdf-schema#subClassOf>
> 	    <http://xmlns.com/foaf/0.1/Document> .
> 	<http://example.com/my-vocab#title>
> 	  <http://www.w3.org/2000/01/rdf-schema#subPropertyOf>
> 	    <http://purl.org/dc/terms/title> .
> Then by strapping an RDFS processor on to our RDFa pipeline, we can add
> the following two triples to our RDFa output:
> 	<>
> 	  <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
> 	    <http://xmlns.com/foaf/0.1/Document> .
> 	<>
> 	  <http://purl.org/dc/terms/title>
> 	    "Foo"@en .
> Which were the triples we wanted.
> Yes, I realise RDFS reasoning is not necessarily a simple thing to
> implement, but given a choice between:
> 1. default prefixes: perform very RDFa1.0-like parsing, then, if you
> want to, perform (perhaps only limited) RDFS reasoning later on in the
> toolchain.
> 2. profiles: add recursive HTTP fetching, parsing and RDF querying to
> the RDFa parser itself.
> I'm still not convinced that #2 is really the simplest option. I'm not
> saying that I can't be convinced, just that I'm not convinced so far.
> Bundling multiples ontologies/vocabularies is a great idea, but @profile
> is not the only way to do it, and not necessarily the best way to do it.


Ivan Herman, W3C Semantic Web Activity Lead
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Received on Monday, 22 March 2010 10:37:25 UTC

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