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Re: [foaf-protocols] Standardising the foaf+ssl protocol to launch the Social Web

From: Bruno Harbulot <Bruno.Harbulot@manchester.ac.uk>
Date: Tue, 06 Jul 2010 19:40:35 +0200
Message-ID: <4C336A93.8050005@manchester.ac.uk>
To: Kingsley Idehen <kidehen@openlinksw.com>
CC: Thomas Roessler <tlr@w3.org>, Tim Berners-Lee <timbl@w3.org>, Harry Halpin <hhalpin@w3.org>, foaf-protocols@lists.foaf-project.org, Ivan Herman <ivan@w3.org>, Ian Jacobs <ij@w3.org>, Jeffrey Jaff <jeff@w3.org>, www-archive <www-archive@w3.org>, Henry Story <henry.story@gmail.com>

On 06/07/2010 18:14, Kingsley Idehen wrote:
> Bruno Harbulot wrote:
>> Hi all,
>> I'll start by a list of points that could be standardized (open
>> questions).
>> First, on the authentication part:
>> 1. Standardizing the representation format: RDF/XML, RDFa, N3?
>> We do need a common format that representation consumers must be
>> able to understand and that representation publishers must
>> produce. We've had issues with the libraries we've used. I think
>> it's fair to say that existing RDF libraries can generally accept
>> RDF/XML more often or better than they accept RDFa or N3.
> Bruno,
> Data representation has to be negotiable.
> For sake of removing content negotiation requirement we should have
> defaults (or example/suggested representations) such as; HTML+RDFa,
> N3/Turtle, and RDF/XML.
> But we shouldn't bind the protocol to any of the above.

Sorry, I disagree. Sure, negotiating the data representation is fine and
it should be encouraged.
However, when it comes to software agents, we need to be sure that the
format negotiation process will converge. Either the publishers
need to publish in at least one format that the software agents must
understand, or all software agents must be able to understand all the
possible formats the publishers may produce. (Here, the software agent,
is the client that gets the WebID document to verify the ID.)

Imagine that:
  - your WebID host can only produce HTML+RDFa and N3,
  - the website to which you're trying to authenticate has a software
agent verifier that can only process RDF/XML.

You can have a nice negotiation system (HTTP content-negotiation or
otherwise). If the implementation of the WebID host can only produce 
HTML+RDFa and N3, and if the implementation of the verifier can only 
process RDF/XML, the negotiation will not conclude. If the negotiation 
doesn't result in a format that the verifier can understand, you won't 
be able to log on.

Henry also said:
> Oddly enough, choice of formats are no longer an issue once one has
> understood the semantic web. GRDDL for example allows any xml format
> to be mapped automatically to rdf. This is for many computer
> scientists a very odd result. It took me some time to believe it. It
> is very liberating when understood. :-)

This sounds fine in theory, but in practice, when it comes to something 
that is to be processed by software agents (independently of the 
programming language), we can't really make the assumptions that these 
conversions will happen by magic and that implementations will support it.
We need a common denominator regarding what the libraries will be able 
to support.
As far as I'm aware, most RDF libraries support RDF/XML fairly well, but 
when it comes to HTML+RDFa, N3, Turtle, support is uneven depending on 
the library and the programming language.

If we say something like "implementations may support any of these 
formats", we'll potentially end up with two implementations that can 
comply with the specification and be unable to talk to each other, which 
would be a bad thing.

Best wishes,

Received on Tuesday, 6 July 2010 18:01:30 UTC

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