Re: Request to publish HTML+RDFa (draft 3) as FPWD

Tue, 22 Sep 2009 13:08:55 -0700



Jonas Sicking wrote: 

I would say there are two separate things that are missing:

The most substantial one is how to do prefix mappings in a DOM or a
HTML document. Prefix mapping is currently defined using the
Namespaces in XML recommendation. However this recommendation only
defines how prefix mappings are done in a serialized XML document. I
hope we can all agree that neither DOMs (an in-memory datastructure)
or HTML documents are not XML documents.

For example, if I have a DOM and I want to do map the prefix "foo",
which of the following algorithms should I use:
1. Call Node.lookupNamespacePrefix as defined by DOM Level 3 using
"foo" as the prefix argument.
2. Walk up the parent chain looking for an element with an attribute
with localName "foo" and namespace "http://www.w3.org/2000/xmlns/",
and then use the value of that attribute.
3. Walk up the parent chain looking for an element with an attribute
with tagName "xmlns:foo", and then use the value of that attribute.
4. Walk up the parent chain looking for either the attribute in 2 or
3, and if both are specified use some prioritization order.
5. Walk up the parent chain looking for either the attribute in 2 if
the document was parsed as XHTML, or attribute in 3 if the document
was parsed as HTML.
6. Do something else?

Any of 1 to 5 (as well as possibly 6) seems equally valid to me, and
as far as I can tell there really is no specified answer.
Nor should there be.  This presupposes a DOM-based processing model.  While you *might* be using a DOM, you don't need to.  Section 2 of Manu's spec is pretty clear about this, as is the HTML5 spec itself.  To answer your question though - it would depend on what environment you were implementing in, surely. If you were writing an implementation against a DOM 3 implementation that actually worked, they 1 seems pretty clever.  An area I wold agree needs clarification is what happens in the (pathological) case where there are two attributes on the same element (your item 4).  The task force has not yet discussed this case. My gut tells me that the item in the XMLNS Namespace would take precedence, but that's not always reliable.

Likewise, how do I find out what the 'cc' prefix is mapped for the <a>
element in the following serialized HTML document?

<!DOCTYPE html>
<html xmlns:cc="http://example.org/myNamespace#">
<head><title>HTML+RDFa example</title></head>
<body>
<table xmlns:cc="http://creativecommons.org/ns#">
<a rel="cc:license"
 href="" class="moz-txt-link-rfc2396E" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">"http://creativecommons.org/licenses/by-nc-nd/3.0/">
 Creative Commons License
</a>
<tr><td>Example table</td></tr>
</table>
</body>
</html>
Manu's document specifies that, in the context of the HTML host language, the document is processed as defined in HTML.  That document requires that a conforming processor have parsed the *input* using the rules specified in HTML5.  A conforming RDFa Processor would not ever see a document with the above structure, right?

As far as I can see the Namespaces in XML recommendation can't help me
in either situation. For the DOM it doesn't deal with in-memory data
models at all, rather it only deals with serialized XML documents. For
the HTML document, if I try to apply XML processing as prescribed by
Namespaces in XML, I conclude that 'cc' maps to
"http://creativecommons.org/ns#", when in reality suspect it should
map to "http://example.org/myNamespace#".
According to Manu's document, and therefore according to HTML5, the "a" element would be moved before the table element, and your suspicion would be correct.


The second, IMHO lesser problem, is that no processing is defined
anywhere for non XML documents. Even as far as reading a rel attribute
out of a document is only defined for XML documents. All normative
requirements refer to XML processing and thus applies no more to HTML
documents than to GIF images. I consider this less of a problem
because I think it's fairly obvious that data is read out of a DOM
using the getAttribute function. And from a HTML document by first
parsing it to a DOM and then calling getAttribute. But it really
should be formally defined somewhere.
Great!  it is formally defined.  In Manu's document, and by reference in the HTML5 spec.  Am I missing something here?  Section 2 of Manu's document says, in part:

"The HTML5 and XHTML5 DOM, or equivalent data structure, should be used as input to the RDFa processing rules. The normative language for construction of the HTML5 DOM and XHTML5 DOM is contained in the HTML5 specification. "

Do you need additional language to make this clearer?

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Shane P. McCarron                          Phone: +1 763 786-8160 x120
Managing Director                            Fax: +1 763 786-8180
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