[whatwg] Annotating structured data that HTML has no semantics for

Tab Atkins Jr. jackalmage at gmail.com
Tue May 12 10:30:27 PDT 2009

On Tue, May 12, 2009 at 5:55 AM, Eduard Pascual <herenvardo at gmail.com> wrote:
> Third issue: also a flaw inherited from RDFa, it can be summarized as
> completelly ignoring the requirement I submitted to this list on April
> 28th, in reply to Ian asking us to review the use cases [1]. I'll try
> to illustrate it with a example, inspired by the original use-case:
> Let's say someone's marking up a collection of iguanas (or cats, or
> even CDs, doesn't really make a difference when illustrating this
> issue), making a page for each iguana (or whatever) with all the
> details for it; and then making an "index" page listing the maybe 20
> iguanas with their name, picture, and link to the corresponding page.
> Adding micro-data to that "index", either with RDFa or with Ian's
> microdata proposal, would involve stating 20 times in the markup
> something like "this is the iguana's picture; this is the iguana's
> name; and this is the iguana's URL". It would be preferable to be able
> to state something like "each (row) <tr> in the <table> describes an
> iguana: the <img>s are each iguana's picture, the contents of the
> <a>'s are the names, and the @href of the <a>'s are the URLs to their
> main pages" just once. If I only need to state the table headings once
> for the users to understand this concept, why should a micro-data
> consumer require me to state it 20 times, once for each row?
> Please note how such a page would be quite painful to maintain: any
> mistake in the micro-data mark-up would generate invalid data and
> require a manual harvest of the data on the page, thus killing the
> whole purpose of micro-data. And repeating something 20 (or more)
> times brings a lot of chances to put a typo in, or to miss an
> attribute, or any minor but devastating mistake like these.

Well, he didn't quite *ignore* it - he did explicitly call out that
requirement to say that his solution didn't solve it at all.  He also
laid down the reason why - it's unlikely that any reasonable simple
in-place metadata solution would allow you to do that.  You either
need significant complexity, some reliance on language semantics (like
tables can rely on their headers), or moving to out-of-band
specification, likely through a Selectors-based model.

The last is likely the best solution for that, and is even easier to
implement within Ian' simplified proposal.  I don't see a good reason
why that can't advance on a separate track, as (being out-of-band) it
doesn't require changes to HTML to be usable.

I floated a basic proposal for Cascading RDF[1] several months ago,
and someone else (I think Eduard?  I'd have to check my archives) did
something very similar.

[1]: http://www.xanthir.com/rdfa-vs-crdf.php


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