[whatwg] Microdata feedback

[Ian Hickson]

On Tue, 12 Jul 2011, Henri Sivonen wrote:
> On Thu, 2011-07-07 at 22:33 +0000, Ian Hickson wrote:
> > The JSON algorithm now ends the crawl when it hits a loop, and 
> > replaces the offending duplicate item with the string "ERROR".
> > 
> > The RDF algorithm preserves the loops, since doing so is possible with 
> > RDF. Turns out the algorithm almost did this already, looks like it 
> > was an oversight.
> 
> It seems to me that this approach creates an incentive for people who 
> want to do RDFesque things to publish deliberately non-conforming 
> microdata content that works the way they want for RDF-based consumers 
> but breaks for non-RDF consumers. If such content abounds and non-RDF 
> consumers are forced to support loopiness but extending the JSON 
> conversion algorithm in ad hoc ways, part of the benefit of microdata 
> over RDFa (treeness) is destroyed and the benefit of being well-defined 
> would be destroyed, too, for non-RDF consumption cases.

The "problem" here is that RDF and microdata have different data models, 
and RDF cannot represent microdata's data model with fidelity.

For example, consider how this converts to RDF and compare it to the 
microdata equivalent:

   <div itemscope itemtype="http://example.com/" itemid="http://example.com/1">
    <span itemprop=a>x</span>
   </div>
   <div itemscope itemtype="http://example.com/" itemid="http://example.com/1">
    <span itemprop=b>x</span>
   </div>

There are other things RDF can't represent easily, e.g. it cannot easily 
represent the order of the values in this item:

   <div itemscope itemtype="http://example.com/">
    <span itemprop=a>1</span>
    <span itemprop=a>2</span>
   </div>

As such, I suggest we not worry about the itemref="" loop case, or that we 
try to fix all these cases together (not sure how we'd fix them).

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'