[foaf-protocols] First WebID Teleconference minutes (July 27th 2010)

Henry Story henry.story at gmail.com
Tue Aug 3 12:01:14 CEST 2010


On 3 Aug 2010, at 11:34, Nathan wrote:

> Henry Story wrote:
>> On 3 Aug 2010, at 11:03, Kingsley Idehen wrote:
>>>> back to it then, what does WebID require to operate on the representation side? to function it has to be 'MUST xxxxxxx' what's the xxxxxxx and is it tightly defined enough to ensure the protocol can function globally? - do we have any agreement?
>>> Yes, but a real technical spec wouldn't and shouldn't negate HTTP's essence.
>>> 
>>> If you note, content negotiation is seen as a problem hence this protracted discussion about data serialization formats.
>>> 
>>> Content negotiation is the key to taking away the preoccupation with specific data serialization formats via MUST statements.
>>> 
>>> Today, Web Browsers default to HTML, and this won't change re. WebID protocol -- even without a MUST for HTML+RDFa.
>> Hi, I think we are very much more in agreement really than we think. Content Negotiation is absolutely key, and means that on the web things are a lot more flexible that most people understand. I am completely with Kingsley on this. The trick will be to find the right wording in the document to express this in a light way, so that people who don't understand this, don't even realise that there was a problem.
> 
> Yup, I think we always are all in agreement with pretty much everything, but just struggle to write it down in a way we all agree covers all the different things which we agree upon..
> 
> To throw in a useless analogy - it's very much like getting dressed, we all agree we should wear clothes, and we all agree that we should wear different clothes for different occasions, sometimes we even need to negotiate what we wear in a particular scenario based on what others require from us.

yes indeed, a very apt analogy. From David Lewis' Convention page 6

[[
Suppose several of us have been invited to a party. It matters little
to anyone how he dresses. But he would be embarrassed if the others 
dressed alike and he dressed differently, since he knows that some 
discreditable explanation of that difference can be produced by whoever
is so inclined.  So each must dress according to his expectations about how
the others will dress: in a tuxedo if the others will wear tuxedos, in a
clown suit if the others will wear clown suits (and in any way he pleases
if the others will dress in diverse ways)
]]

http://books.google.com/books?id=UHADV9OkdeIC&lpg=PP1&dq=david%20lewis%20convention&pg=PA8#v=onepage&q&f=false

> 
> Strangely, I feel better for saying that - but overall +1 to everything and what the hell do we write in that paragraph that we all agree on?
> 
> [[[
> A Verification Agent must be able to process documents in RDF/XML [RDF-SYNTAX-GRAMMAR] and XHTML+RDFa [XHTML-RDFA]. A server responding to a WebID Profile request should support HTTP content negotiation. The server must return a representation in RDF/XML for media type application/rdf+xml. The server must return a representation in XHTML+RDFa for media type text/html or media type application/xhtml+xml. Verification Agents and Identification Agents may support any other RDF format via HTTP content negotiation.
> ]]]

I don't think we need to be putting SHOULDs and MUSTS all over the place like that. It feels like someone is thinking that we will win awards for spec-likeness the more we have of those.

A few more specific comments on the above paragraph:

> A Verification Agent must be able to process documents in RDF/XML [RDF-SYNTAX-GRAMMAR] and XHTML+RDFa [XHTML-RDFA].

A Verifications agent should be able to process the standard RDF formats.
Currently RDF/XML and RDFa are formally accepted specs. [[ TODO: specify how the GRDDL spec can play here -- this is going to take some time, we don't have good examples yet.]]

> A server responding to a WebID Profile request should support HTTP content negotiation.

I would put it in different because for one HTTP just cannot not support content neg - it's part of the protocol. 

If the above is trying to say is something along the lines I suppose that the server should serve more than one representation, then I disagree. 

"A server should server at the WebID profile URL a document in a format that
has a well known mapping to RDF. Well known mappings are currently the formally
supported W3C serialisations RDF/XML and RDFa. Other formats need to have an automatically discoverable translation into RDF using something like GRDDL [[ To be looked at in a lot more detail. Will require working with some other w3c groups to get this right. Note: we support XSPARQL as a format for effiently doing this]]"

So we have a coordination problem, as explained in David Lewis' book Convention.
The publisher must publish in a format that most parsers will understand, if he is not to be denied access to cool parties. And the parser must understand most formats published, if he is not to loose friends. 

Of course the client should not be so lenient as to accept any format, with no clear semantics on the danger that he won't otherwise have any security at all.

> The server must return a representation in RDF/XML for media type application/rdf+xml. The server must return a representation in XHTML+RDFa for media type text/html or media type application/xhtml+xml. Verification Agents and Identification Agents may support any other RDF format via HTTP content negotiation.

yes, though really that's just the definition of content negotiation. :-)
So no need to sound so formal here, we are just explaining what another spec is saying. We can have a paragraph like that to explain content/neg if needed.

> ]]]




> 
> That one ^^
> Best,
> 
> Nathan
> 
>> Here is how David Lewis opens up his book on Convention.
>> "It is the profession of philosophers to question platitudes that others accept without thinking twice. A dangerous profession, since philosophers are more easily discredited than platitudes, but a useful one. For when a good philosopher challenges a platitude, it usually turns out that the platitude was essentially right; but the philosopher has noticed trouble that one who did not think twice could not have met. In the end the challenge is answered and the platitude survives more often than not. But the philosopher has done the adherents of the platitude a service: he has made them think twice."
>> So we have something very similar going on with respect to the web and semantics. Most people don't quite get how the web is really working. They all use it without trouble. From time to time, in architectural situations like this one, when protocols are developed we reveal the underlying complexities - or one could even say the even more beautiful, but slightly unsettling underlying simplicity! In the end though things will continue to work the way unreflecting people assumed it did most of the time. In fact it is because people have a tendency to see only syntax, that the conversion to a few syntaxes is nearly given in advance. But we don't need to be obsessive about that. We can just describe how things ARE. And currently all our implementations use RDFa and rdf/xml. It is therefore not a lie to say, that you wont' interoperate very well with us if you don't support those.
>> But are those formats necessary to the protocol? Not really...
>> Henry
> 



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