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Re: Discussion with Ian and Henri about HTML5+RDFa (part 2/2)

From: Toby Inkster <tai@g5n.co.uk>
Date: Mon, 26 Jan 2009 13:30:44 -0000 (UTC)
Message-ID: <62461.>
To: "Dan Brickley" <danbri@danbri.org>, "Ben Adida" <ben@adida.net>, "Manu Sporny" <msporny@digitalbazaar.com>, "RDFa mailing list" <public-rdf-in-xhtml-tf@w3.org>, "Ian Hickson" <ian@hixie.ch>, "Henri Sivonen" <hsivonen@iki.fi>, "Mark Birbeck" <mark.birbeck@webbackplane.com>, "Sam Ruby" <rubys@intertwingly.net>

San Ruby wrote:

> Henri and Dan have noted that by accepting "xmlns:html='html'" and
> limiting oneself to full URIs you get to the point where you have a
> document which can be processed correctly by many RDF parsers.

To be pedantic, it's xmlns:http="http:" (Note the colon in the attribute

As far as I can see, it's a reasonable compromise. RDFa parsers will
probably need some updating for HTML5 anyway (e.g. the proposed @prefix),
so it shouldn't hurt to include this.

I'd suggest not specifying it in a way that says that there is a
hard-coded xmlns:http="http:" on the root element though. It should be
hard-coded at an imaginary level "above" the root element, thus allowing
authors to override it if need be (e.g. there is the HTTP-in-RDF
vocabulary that allows for HTTP requests and responses to be described in

In terms of the RDFa syntax document's processing sequence it could be
implemented by making the list of URI mappings non-empty in the initial
evaluation context. <http://www.w3.org/TR/rdfa-syntax/#sec_5.5.>

> What other desirable and undesirable social effects would there be by
> identifying a registry for well-known namespaces?

When a new prefix was added to the registry, it would presumably take
weeks, months or even years for it to trickle down to RDFa parsers.
(Unless the registry was machine readable and RDFa parsers were obliged to
query it frequently, which would create a central bottleneck of precisely
the type that RDF was designed to avoid.)

During the trickle-down period, authors would be wary of using the prefix,
as their experience using it would be inconsistent.

I don't think an evolving list of default prefixes is a good solution,
though a static list of pre-defined prefixes is workable, provided authors
have a mechanism such as @prefix to define their own prefixes and override
the predefined ones.

Toby A Inkster
Received on Monday, 26 January 2009 13:31:25 UTC

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