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My no-longer pseudo code, the way I understand it:-)

From: Ivan Herman <ivan@w3.org>
Date: Sat, 04 Aug 2007 16:48:42 +0200
Message-ID: <46B491CA.1020303@w3.org>
To: W3C RDFa task force <public-rdf-in-xhtml-tf@w3.org>
Hi everybody,

I had some further fun with what I talked about in [1]: it is now
operational. I tested in on some of my own files on my machine. I still
have to go through the formal tests on RDFa (I hope to be able to do
that next week, because I will be out after that).

The URI I had in [1], namely [2], is no longer valid. To make things
clearer and more manageable, I have indeed separated some
functionalities in separate Python modules, so I have a small Python
package instead, consisting of few files; you can look and download them
in [3]. The core of the processing is the file 'Parse.py'; 'Literal.py'
implements the agreement we have based on [4]; and 'State.py' takes care
of namespace, xml:base, language, etc, handling for a specific node.

'Parse.py' implements that current agreement we, I believe, have, namely
[5]. I am very curious to see how this matches the understanding of
others. B.t.w., even if you do not 'speak' Python, I hope the code is
understandable by itself, I tried to make it readable and commented.

Of course, one of the good features of such exercise is that it reveals
some edge cases and questions.

- I see it as a good sign that the core processing can be done in a
relatively short and straightforward code. I think having RDFa doable
easily _is_ a very important issue and, if this implementation as well
as the other up-to-date ones (eg, Ben's) are o.k., we should begin to
resist any new feature that would complicate implementations too much:-)

- I did *not* implement any kind of CURIE type processing (I mean,
handling '[' and ']' characters in the references). For @href, @resource
and @about I simply considered those as URI-s; for @rel, @instanceof,
@property, @rev, I just considered them as essentially qnames.
Essentially, because I do not check anything on syntax and I just use
the qname structure to concatenate strings. After all, this is all that
RDF requires. I do not think we need anything else at the moment
(remember that I am not particularly interested in having the _:123 kind
of feature for bnodes, I think we _can_ live without those).

- I know we found some side-effects with Ben on @about that were
strange, and one possible approach was to take out @about from [5]. In
fact, that was my first implementation, but I then decided to stick to
[5] (for now). We will have to see what it leads to with the test cases
and whether it is worth the trouble to do something more complicated.

- I implemented the container and collection handling as I described it
in [6]. It just works:-)

- I am not sure that whether we decided on what should happen with
@rel="", @instanceof="", etc. My proposal is: nothing. Eg, if @rel=""
happens then the algorithm for determining a new subject for enclosed
elements, as described in [5], kicks in, but no triple is added to the
graph because the property URI is empty.

This has an interesting and (very!) positive side-effect. You may
remember I had the problem of how to generate:

<> foo:bar [
   a rdf:Seq;
   rdf:_1 [ q:p "something" ].

which led to my proposal on "_:" for an anonymous blank node. Well, if I

<ul instanceof="rdf:Seq">
<li instanceof=""><span property="q:p">something</span></li>

this is exactly what is generated. Why? The rules in [6] say that the
<ul> above is a shorthand for

<ul instanceof="rdf:Seq">
	<li rel="rdf:_1" instanceof="">
		<span property="q:p">something</span>

The rules in [5] dictate that a blank node must be generated for the
<li>, but with the additional rule above it also says that no triple for
rdf:type is added to the graph because @instanceof="". VoilĂ ! Ie: I
hereby withdraw my proposal for "_:" (if we accept the rule above, that

If you want to install it and test it (you are welcome to do so!), be
sure you have rdflib[7] installed. Be warned, however: it seems that
both the 'pretty' xml serialization and the turtle serialization in
RDFLib has some problems (the default, pure "xml" works). The 'pretty'
RDF/XML leads to bugs in some cases (notably for Lists), whereas the
turtle is overzealous in defining @prefix statements and this produces
some pretty unreadable code in some cases.

Sorry for the long mail (again)



[2] http://www.w3.org/2007/08/rdfa.py
[3] http://dev.w3.org/2004/PythonLib-IH/pyRdfa/
[4] http://www.w3.org/2006/07/SWD/wiki/RDFa/LiteralObject
[7] http://rdflib.net


Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Saturday, 4 August 2007 14:48:45 GMT

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