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Re: The Deferred Resolution Graph

From: Ivan Herman <ivan@w3.org>
Date: Mon, 22 Mar 2010 12:35:20 -0400
Message-ID: <4BA79C48.8090804@w3.org>
To: Manu Sporny <msporny@digitalbazaar.com>
CC: RDFa WG <public-rdfa-wg@w3.org>
Manu,

On 2010-3-21 12:39 , Manu Sporny wrote:
> On 03/20/2010 06:07 AM, Ivan Herman wrote:
>> But then we are discussing three proposals, aren't we?
> 
> Not necessarily... more below.
> 
>> On 2010-3-19 21:31 , Manu Sporny wrote:
>> [skip]
>>>
>>> * RDFa vocabulary proposal (Ivan/Manu)
>>> * @token proposal (Mark)
>>> * Default prefix proposal (Toby/Martin)
> 

I think that default prefix proposal is different and actually
orthogonal to the other two (you yourself rebut the merge of that one
with others...)

I think the choice is between the 1st and the 2nd, essentially on the
issue of context specific interpretation of the @profile file. We can
then have the default prefix possibility, _too_ (and I actually believe
having some sort of a @profile plus that actually makes sense)

Ivan


> We could reconcile the RDFa vocabulary proposal and the default prefix
> proposal by doing this:
> 
> <p profile="http://example.com/my-vocab#"
>    about="#curious-character" typeof="Book">
>    <span property="title">Surely You're Joking, Mr. Feynman!</title>
> </p>
> 
> The example above mixes the Bibliography (Book) and Dublin Core (title)
> ontologies. There are two cases that we're interested in:
> 
> 1. What happens when you can dereference the @profile?
> 2. What happens when you can't dereference the @profile?
> 
> What happens when you can dereference the @profile
> --------------------------------------------------
> 
> This is the easiest and most straight-forward case. If you can
> dereference the @profile, assuming error-free profile and author
> documents, you will have the set of mappings and thus can generate the
> proper RDF triples *in the default graph*:
> 
> <#curious-character>
>    rdf:type
>       bibo:Book .
> 
> <#curious-character>
>    dc:title
>       "Surely You're Joking, Mr. Feynman!" .
> 
> I don't think anybody would argue that this is ideally what we want to
> happen. This always works as long as the @profile document is available
> (via ad-hoc download, via an application ontology cache, via a ontology
> backup service, or if the @profile document triples are hardcoded in the
> parser).
> 
> What happens when you cannot dereference the @profile
> -----------------------------------------------------
> 
> This is the case that the default prefix approach excels at addressing.
> At this point, let's introduce a completely new concept called the
> "Deferred Resolution Graph" (DRG). This graph is where triples that
> cannot be resolved, due to @profile document dereferencing issues, are
> placed until the @profile document that they depend on can be retrieved.
> 
> Let's assume that @profile has the added semantics of @vocab as Toby has
> defined in this e-mail:
> 
> http://lists.w3.org/Archives/Public/public-rdfa-wg/2010Mar/0174.html
> 
> Therefore, the following markup:
> 
> <p profile="http://example.com/my-vocab#"
>    about="#curious-character" typeof="Book">
>    <span property="title">Surely You're Joking, Mr. Feynman!</title>
> </p>
> 
> would produce the following triples, if the @profile document can be
> retrieved, *into the default graph*:
> 
> <#curious-character>
>    rdf:type
>       bibo:Book .
> 
> <#curious-character>
>    dc:title
>       "Surely You're Joking, Mr. Feynman!" .
> 
> If the @profile document *cannot* be retrieved, the following triples
> would go *into the deferred resolution graph*:
> 
> <#curious-character>
>    rdf:type
>       <http://example.com/my-vocab#Book>^^UNRESOLVED .
> 
> <#curious-character>
>    <http://example.com/my-vocab#title>^^UNRESOLVED
>       "Surely You're Joking, Mr. Feynman!" .
> 
> Those triples in the *deferred resolution graph* could only be placed
> into the *default graph* once the UNRESOLVED URIs are resolved at some
> point (via ad-hoc download at a different time, via an application
> ontology cache, or via an ontology backup service).
> 
> Conclusion
> ----------
> 
> So Ivan, while you stated that we are talking about three different
> proposals, I hope that this demonstrates that the RDFa vocabulary
> proposal and the default prefix proposal can be combined with relative
> ease to produce a hybrid approach that produces the benefits of both
> approaches.
> 
> Note that while I took the time to outline the possible deferred
> resolution graph concept, I think it's a bad idea for a number of reasons.
> 
> -- manu
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
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Received on Monday, 22 March 2010 16:34:22 GMT

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