TAG issue on HTML+RDFa and Microdata last call drafts


Arising from its Last Call review of the HTML5 suite of specifications, the 
TAG wishes to raise issues on both the HTML microdata [1] and HTML+RDFa 1.1 
[2] Working Drafts.

Specifically, our opinion is that the W3C should not publish two 
specifications that meet such similar requirements in incompatible ways. We 
think doing so would cause confusion for users and implementers, promote 
lock-in, and fragment the web. We request that the W3C Director set up a 
task force to find agreement on a way forward.


The RDF data generated by microdata and RDFa processors is different both 
for documents containing no additional data markup and for documents that 
contain RDFa. This incompatibility might possibly be remedied by removing 
the relevant sections from the microdata specification, but there are 
deeper problems that arise from the fact that the two technologies do much 
the same thing in different ways. Users find it hard to choose which to 
use. It is hard for users to move between them because they are outwardly 
very similar but have differences in parsing algorithms that are not 
immediately obvious. From a publisher's point of view, using both within a 
document leads to repetition; using only one means locking yourself into a 
particular technology stack and set of consumers. Similarly, from an 
implementer or consumer's point of view, implementing both increases code 
quantity and complexity, but implementing only one excludes potential 
customers or data providers.

Both specifications come from a community interested in publishing and 
consuming structured data within Web pages. The TAG's purpose here is not 
to comment on the relative merits of the technologies, nor to signal 
whether one or the other might have preferred status due to history of 
deployment. Rather, we are raising the issue that the W3C has before it two 
Last Call Working Drafts specifying capabilities that overlap and that will 
cause incompatibilities if deployed together. It would be irresponsible for 
the TAG not to attempt to help the community to reconcile the two 

We therefore suggest that W3C create a task force of people who are 
knowledgeable about publishing, processing and consuming structured data, 
including those invested in microdata, RDFa and microformats, to provide 
input and focus to the HTML WG in aligning the two specifications. We 
suggest the task force investigate options including, but not limited to:

   * combining RDFa and microdata into a single language with two 
conformance levels, with consistent processing between the two that enable 
advanced users to use more complex features that are recognised by advanced 
processors, without rendering their data invisible to simpler processors

   * combining RDFa and microdata into a single language that is a middle 
ground between the two technologies

   * retaining both microdata and RDFa as separate syntaxes, but ensuring 
that there is a clear story that enables users and implementers to choose 
which to use or implement, that both can be used within the same document 
without incompatibility in the RDF that is generated from them, that as 
much code as possible can be reused in their implementation, and that users 
can easily transition between the two syntaxes

The task force should be tasked to strive towards compatibility with other 
W3C specifications, particularly HTML5. It should also take into 
consideration other existing specifications, and impacts on existing user 
and implementer communities.

Thank you very much.

Noah Mendelsohn
for the W3C Technical Architecture Group

[1]: http://www.w3.org/TR/2011/WD-microdata-20110525/
[2]: http://www.w3.org/TR/2011/WD-rdfa-in-html-20110525/

Received on Friday, 24 June 2011 15:05:17 UTC