W3C home > Mailing lists > Public > public-rdf-in-xhtml-tf@w3.org > August 2007

Action item to outline language-dependent features

From: Mark Birbeck <mark.birbeck@formsPlayer.com>
Date: Thu, 16 Aug 2007 12:12:22 +0100
Message-ID: <a707f8300708160412y5fe0e6b2hffbe38865484da60@mail.gmail.com>
To: "W3C RDFa task force" <public-rdf-in-xhtml-tf@w3.org>

Hello all,

A few issues have come up recently where some feature or other might
be used by RDFa, but it would be inappropriate to provide that feature
within RDFa itself. For example, we would like to be able to express
the language of literals, but it would be overkill (and confusing) for
us to create our own language attribute when both HTML and XML-based
languages have such a facility.

Another example is the use of @xml:base in XML languages; this allows
fine-grained control over relative paths in mark-up and is a very
useful feature for RDFa to leverage, but if a host language does not
provide it then I think we have to accept that limitation, and not
provide it ourselves.

We discussed on a telecon recently that one way to approach this whole
thing is to define some kind of abstract set of properties that a host
language would provide, and then to map those to specific attributes.

My suggestion would be to define a 'context' that is then used by RDFa
parsers, in much the same way that the definition of XPath indicates a
context for evaluating expressions.

The properties of the 'context' that we would need for RDFa are (there
are no doubt others that I have missed):

  * a current langauge, or 'no language';

  * a current subject;

  * a current base URI against which relative paths are evaluated;

  * a set of prefix/substitution mappings.


In HTML these context-features would be set in the following way:

  * language is set using @lang;

  * subject is set using various rules, such as @href, @resource, @about,
    @src, @rel/@rev, and so on;

  * the base URI is set using the current document URL or <base>;

  * prefix/substitution mappings are provided by ... :)

(This last point is still not quite resolved, but there are proposals
floating around.)


In XHTML the context-features are set as follows:

  * language is set using @xml:lang;

  * subject is set using various rules, such as @href, @resource, @about,
    @src, @rel/@rev, and so on;

  * the base URI is set using the current document URL, <base> or @xml:base;

  * prefix/substitution mappings are provided by @xmlns.

I'm hoping that we can come up with precise names for these
context-features (and others that I have no doubt missed) so that we
can define the processing rules very clearly, independent of the
attributes. We can then also define the behaviour of the attributes in
terms of these definitions.

For example, you might define @resource simply by saying "it sets the
context subject property for all contained RDFa expressions", and that
might be all that is needed. Then in the processing rules you might
say "a triple is generated by combining the context subject property
with the blah blah", and not make any reference to host
language-specific attributes.

Regards,

Mark

-- 
  Mark Birbeck, formsPlayer

  mark.birbeck@formsPlayer.com | +44 (0) 20 7689 9232
  http://www.formsPlayer.com | http://internet-apps.blogspot.com

  standards. innovation.
Received on Thursday, 16 August 2007 11:12:28 GMT

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