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Re: ISSUE-1: What happens when you can't dereference a profile document?

From: Ivan Herman <ivan@w3.org>
Date: Fri, 12 Mar 2010 11:24:15 +0100
Message-ID: <4B9A164F.2010006@w3.org>
To: Toby Inkster <tai@g5n.co.uk>
CC: Manu Sporny <msporny@digitalbazaar.com>, RDFa WG <public-rdfa-wg@w3.org>
Hi Toby,

general question: do you have somewhere a writeup of what is the
mechanism you have in mind? Because, frankly, I do not really understand
how your fallback would exactly work.

In general, I find the issue of a missing link compelling but I am not
100% sure that we should go down the line of making fallback
specification. I am just concerned about the possibly high cost of
specifications that would require...

As for the several vocabulary question below:

On 2010-3-11 20:47 , Toby Inkster wrote:
> A big question that needs to be answered before we can determine whether
> this is feasible is: how many profiles can be active at once?
> e.g. given:
> 	<div profile="a">
> 	  <div profile="b">
> 	    <span typeof="Foo" property="bar" resource="[baz]" />
> 	  </div>
> 	</div>
> Let's assume that profile 'a' defines 'Foo' and 'bar'; and profile 'b'
> defines 'bar' and 'baz'.

My model has always been the same as, say, the usage of xmlns. This is
also in line with the way the processing model works today, by having a
local copy of the uri mappings that is pushed down to the children of a
specific node.

> For 'baz', I don't imagine there is any contention. Profile b's
> definition wins.
> For 'bar' there are three possible outcomes:
> 	- it resolves to profile b's definition only, as the nearest
> 	  ancestor profile;

That is certainly my preferred approach

> 	- it resolves to profile a's definition only, because it "got
> 	  there first"; or
> 	- it generates two triples, using both definitions.
> But what about 'Foo':
> 	- it's treated as typeof="" because the nearest ancestor
> 	  profile does not define it; or
> 	- the parser figures out that b does not define Foo, so
> 	  checks the next ancestor profile for a definition.

That is my preferred approach

Copying the processing steps of the current document what I see happening is

- for the top level div, profile 'a' will generate a number of mappings,
ie, for 'Foo' and 'bar'
- when going to the intermediate div, that node will first inherit the
mapping from the top level, then interprets 'b' by essentially
overriding the definition of 'bar', and adding a definition of 'baz'
- span inherits the mappings of its parent, does not modify it because
there is no 'profile', and resolves the URI-s

This is similar to the way xmlns attributes are treated...

My 2 cents...


> If we make the decision that there's only ever one profile active, then
> when parsing the <span/>, profile 'a' will be ignored, so we get 'Foo'
> undefined, with 'bar' and 'baz' defined by profile 'b'.
> If there's only every one profile active, then generating these fallback
> triples becomes a very easy option, because we know exactly which
> profile was *supposed* to define them.
>> Toby has an alternate mechanism that uses @default-prefix and requires
>> RDFa processors to understand a subset of OWL.
> @default-prefix was just a temporary name for the attribute while we
> were deciding. @profile is fine.
> The subset of OWL required is not much more complicated to implement
> than the current suggested vocabulary for profiles. It's merely a way of
> saying that this term from the profile:
> 	<http://example.com/vocab#Person>
> is equivalent to this one:
> 	<http://xmlns.com/foaf/0.1/Person>


Ivan Herman, W3C Semantic Web Activity Lead
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Received on Friday, 12 March 2010 10:23:45 UTC

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