[whatwg] Trying to work out the problems solved by RDFa

Andi Sidwell andi at takkaria.org
Mon Jan 12 18:09:35 PST 2009

On 2009-01-12 23:15, Toby A Inkster wrote:
> Henri Sivonen wrote:
>> eRDF is very different in not relying on attributes whose qname
>> contains the substring "xmlns".
> eRDF is very different in that it is incredibly annoying to use in real
> world scenarios (i.e. not hypothetical "Hello World" examples).
> Calogero Alex Baldacchino wrote:
>> I guess closing a language to every kind of "back-door changes" may be
>> in contrast with the principle of paving a cawpath. I also guess that,
>> if microformats experience (or the "realworld semantics" they claim to
>> be based on) had suggested the need to add a new element/attribute to
>> the language, a new element/attribute would have been added.
> But Microformats experience *does* suggest that new attributes are
> needed for semantics. Look at the debate around accessibility within
> Microformats which has been going on for ages. Because of the
> Microformats process of working *within* existing HTML standards it has
> not been solved, and I can't see a solution reaching consensus in the
> foreseeable future. HTML5's <time> goes part of the way to solving this,
> but it doesn't address the whole problem like RDFa's "content" attribute
> does.

Right, so some microformats brought to attention a need which HTML5 
could easily solve by adding <time>.  Why does this mean that RDFa 
should be added?

> Another reason the Microformat experience suggests new attributes are
> needed for semantics is the overloading of an attribute (class)
> previously mainly used for private convention so that it is now used for
> public consumption.

But HTML4 itself says that class can be used "for general purpose 
processing by user agents", so this seems to be a weird argument.  If we 
introduced RDFa and it got used, would you argue you need something more 
than RDFa, because it is being used for what it is specced for?

> Yes, in real life, there are pages that use
> class="vcard" for things other than encoding hCard. (They mostly use it
> for linking to VCF files.) Incredibly, I've even come across pages that
> use class="vcard" for non-hCard uses, *and* hCard - yes, on the same
> page! As the Microformat/POSHformat space becomes more crowded,
> accidental collisions in class names become ever more likely.

Right, but is it much of an issue?  If you have a hCard extractor, the 
user can see easily that it's not useful data.  And if doesn't follow 
any of the other rules for an hCard, then the UA can safely ignore it 
(e.g. it has no fields).  In practice, this kind of collision seems 
fairly non-problematic.

> The Microformats community hasn't added any new attributes for
> Microformats, because that was one of the guiding principles when the
> community was established: however, that does not mean it hasn't shown
> that new attributes are needed for encoding rich semantics in HTML. On
> the contrary, I think it's proved that they are.

Given that the only example of the microformats process needing an 
addition to the HTML language has been <time>, I'm not sure that's a 
conclusive proof.


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