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Re: RDFa and Web Directions North 2009

From: Sam Ruby <rubys@intertwingly.net>
Date: Fri, 13 Feb 2009 15:51:25 -0500
Message-ID: <4995DD4D.1040002@intertwingly.net>
To: Mark Birbeck <mark.birbeck@webbackplane.com>
CC: Kingsley Idehen <kidehen@openlinksw.com>, Dan Brickley <danbri@danbri.org>, Michael Bolger <michael@michaelbolger.net>, public-rdfa@w3.org, RDFa mailing list <public-rdf-in-xhtml-tf@w3.org>, Tim Berners-Lee <timbl@w3.org>, Dan Connolly <connolly@w3.org>, Ian Hickson <ian@hixie.ch>, Henri Sivonen <hsivonen@iki.fi>

Mark Birbeck wrote:
> Hi Sam,
> 
>> Ah, at last, a technical discussion!
> 
> He he.
> 
> But with respect, to have a discussion we need to read each other's comments. :)

Somehow we both are making true statements, yet missing each other's points.

> I wrote that the result of defining the specification in terms of
> navigating a DOM rather than in terms of a specific set of angle
> brackets was that:
> 
>   "...there are already a number of parsers available that run within
>   current browsers, even when the host browser is in HTML mode."

And I wrote that "HTML parsing rules differ in visible ways from XHTML. 
  Ways that affect the specific names of attributes chose[sic] in RDFa."

Both are true statements.

> Yet you replied:
> 
>> Sounds great in theory.
> 
> I won't dispute that it sounds great in theory, but the reason I
> mentioned that we have existing browser implementations is to make the
> point that it *already* works...
> 
> ...in practice!
> 
> Anyway, you then continue:
> 
>> Unfortunately, Henri has provided a test case that disproves this in practice:
>>
>> http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2009-January/018242.html
> 
> I don't know quite what it is that you think Henry has 'disproved'. We
> already knew that the there are additional properties relating to
> namespaces that are available in XHTML mode, but that are not
> available in HTML mode.
> 
> Henri gives us a script that when run in HTML mode, doesn't get to use
> those properties...but why is that a surprise?
> 
> In short, if you want to write an RDFa parser in JavaScript, that will
> run in both HTML mode and XHTML mode, you'll need to process the
> attribute names yourself, and keep track of the prefix mappings.
> 
> It's not particularly difficult.

A list of the parsers alluded to above would be helpful as an existence 
proof for the above assertion.  For those who wish to replicate such, it 
would be helpful if the list of differences were enumerated and 
documented somewhere, ideally in a Standard somepace.

My statement was in response to a statement that I have seen often made 
that there are no differences that affect application programmers.  Such 
a statement is provably false.  The people making these statements 
aren't dummies; it simply is the case that the differences are subtle 
and non-obvious and tend to be glossed over by those that know better.

Your recent statement that "I can assure you that the parsing rules were 
very explicitly written in such a way that the only thing they require 
to do their work is a hierarchy of nodes, and the ability to obtain the 
value of an attribute.", while technically true, tends to obscure more 
than reveal when it comes to these differences.

Actually, I say differences.  I only have an existence proof for one 
difference at the moment.  Is there more?  Beats me.  Hence my assertion 
that a definitive list would be helpful.

  - - -

I got pulled into this discussion at a point where it was an appeal to 
authority (presumably TimBL), or a questioning of authority (Hixie). 
Neither are particularly productive ways of proceeding.  And Hixie 
mentions that in theory I could play a role in overruling a decision he 
has made.  All I will say on that point is that I would strongly 
recommend that nobody attempt to pursue that path without first doing 
their homework.

Meanwhile, Manu has a list of use cases.  You apparently know of a list 
of existing parsers.  And if somebody could enumerate the complete list 
of differences between HTML and XHTML that such parsers need to be 
concerned about; well, that could certainly qualify as homework.

> Regards,
> 
> Mark

- Sam Ruby
Received on Friday, 13 February 2009 20:52:03 GMT

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