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Re: attempting to merge the 'vocab' and 'profile' documents

From: Ivan Herman <ivan@w3.org>
Date: Sat, 06 Mar 2010 08:22:19 +0100
Message-ID: <4B9202AB.8060504@w3.org>
To: Mark Birbeck <mark.birbeck@webbackplane.com>
CC: W3C RDFa WG <public-rdfa-wg@w3.org>
Hey Mark,

I am afraid we disagree:-(

The way I see it, what we have is an RDF graph that is used by a
processor that produces _another_ RDF graph by extracting it from some
data. That 'control' RDF graph is there to give additional information
on how that extraction should operate. It is, in this abstract sense,
the same as when one uses an RDF graph to describe how a particular
relational data from an RDB, using a particular Relational Database
Schema, should be extracted to generate an RDF graph (and such systems
do exist already). The two graphs, ie, the 'control' one and the
'target' one, are different; there is no circularity for me. And yes,
you are right that we could use the same mechanism for base (and the
fact that the value may be relative is only an implementation
complication). Of course, there is no reason for doing that because we
already have a well established mechanism to set the base...




On 2010-3-5 17:53 , Mark Birbeck wrote:
> Hi Ivan,
>> It is not my goal to use RDF just to use RDF, obviously. But RDF gives
>> me a way to define both the concepts and the resulting mechanism in an
>> abstract manner that is independent of the serialization. And that is
>> what I think is nice in Manu's original document.
> Of course I agree, and my guess is that every time any of us needs to
> define something, we all reach for RDF. :) After all, just about
> everything can be expressed using triples -- why not the properties
> that guide the creation of triples.
> But then when you delve into this a little deeper, you are left asking
> whether it is actually the right thing to do, to define profile values
> using triples.
> For example, take the notion of 'base' -- the base URI used to guide processing.
> It's expressed in HTML/XHTML+RDFa using the base attribute, and in N3
> using the @base syntax. In my RDFj syntax, I use a property in the
> context object.
> I.e., in all of these situations it's not expressed using RDF.
> Now, you *could* say, what's the big deal? Surely 'base' is just like
> a predicate; we can easily say 'this document has a base of <x>'.
> But what if, when we look at <x> we discover that it's a relative URI?
> What do we make it absolute against? After all, it's the base.
> Perhaps we get round it by saying that the value must always be
> absolute? But then we're no longer dealing with RDF, because there are
> no such restrictions on any other resource URIs in RDF.
> It gradually emerges that 'base' is not a 'property' of the current
> document at all; it's a precondition for extracting the properties of
> the current document. And I believe that this same circularity rears
> its head with other profile properties (although the issues are less
> direct), which is why I think we should avoid this altogether.
> This dicussion is not dissimilar to the argument that took place on
> the list about whether @profile can be expressed as @rel="profile"; I
> believe that the key point is that you need some 'out of band' method
> to express the values that drive processing, and that method needs to
> be distinct from what you are actually processing.
> Regards,
> Mark
> --
> Mark Birbeck, webBackplane
> mark.birbeck@webBackplane.com
> http://webBackplane.com/mark-birbeck
> webBackplane is a trading name of Backplane Ltd. (company number
> 05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
> London, EC2A 4RR)


Ivan Herman, W3C Semantic Web Activity Lead
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Received on Saturday, 6 March 2010 07:22:05 UTC

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