Re: [httpRedirections-57] Resource-Decription Header: a possible proposal to consider.

Stuart,

On 7 Feb 2008, at 14:59, Williams, Stuart (HP Labs, Bristol) wrote:
>> There seem to be two issues worth discussing here:
>>
>> 1. The perceived need for a generic "metadata channel" in HTTP,

Regarding this issue, a lot of motivating use cases and points of pain  
have now been shown elsewhere in the thread, and I was wrong to  
dismiss it.

I still prefer

    Link: <foo>;rel=meta

over

    Resource-Description: <foo>

because the Link header seems much easier to explain and lobby for  
than Resource-Description. “It's just like the <link> element in HTML,  
but it also works on JPEG files and ZIP archives. The header has been  
around since HTTP 1.0, but was removed in HTTP 1.1 because in the late  
1990s almost no one used it.”

Resource-Description, on the other hand, is in danger of being  
dismissed as yet another silly semantic web idea.

So, why not promote the existing and familiar solution, instead of  
reinventing this particular wheel?

>> 2. the perceived need for stronger semantics than 303's
>> "try-over- there".
>
> 3. Validating conformance with the architecture - which is
>   roughly I think what Jonathan/Alan have been asking about
>   (here and elsewhere).

Rest of this mail deals with these issues.

>>> I agree... but if no such expressions are found after diligently
>>> following such a chain, one has no basis for complaint, no stick to
>>> wield to say that any one did anything wrong... one can only  
>>> complain
>>> that they weren't as helpful as the could have been.
>>
>> I don't think that HTTP should come with conformance
>> requirements for the content transported with it.
>
> Firstly, in this respect I was trying to confine the notion of  
> conformance to the definition of a specific header - and not the  
> whole of HTTP. So that *use* of the header in a response is an  
> implicit undertaking to conform with what may be required of its  
> use. That gives a legitimate basis for 'complaint' if for a given  
> use there is a failure to meet those undertakings. Secondly, if  
> there are such undertakings, then there should be an objective means  
> to test whether they have been met. I would couch those in terms of  
> relations that must hold between resources eg. "A :hasDescription  
> B . " (and yes :hasDescription could be used directly in other  
> retrievable representations). The tricky edge case is an apparent  
> description that the recipient is unable to parse/comprehend.

Are objective conformance tests really core to this question? The  
arguments I hear are:

a) HTTP lacks a generic metadata channel, which creates pain in  
scenarios where metadata records are to be associated with arbitrary  
web resources

b) There's a clear way to associate descriptions with  
representationless resources; shouldn't we have one for resources that  
have representations too?

I don't hear:

c) There is no objective means of determining wether the thing at the  
end of a 303 makes sense.

>> AFAIK, HTTP doesn't have any language that discourages
>> 302-redirecting into a 404-responding resource, although
>> obviously doing so is not helpful.
>>
>> AFAIK, HTTP doesn't have any language that discourages
>> serving representations that are wildly inconsistent over
>> time, although obviously doing so is not helpful.
>>
>> IMHO, HTTP shouldn't have any language that discourages
>> serving totally off-topic stuff at the end of a 303, although
>> obviously doing so is not helpful.
>>
>> HTTP is concerned with the transport of representations of resources.
>> The nature and relationships of those representations are a
>> separate concern.
>
> I sort of hear you thumping the table here - maybe that just me  
> hearing the leading CAPs.
>
> The question I hear Alan ask (I'll find a reference if you need one)  
> is how can an agent tell if some deployment (of resources and  
> descriptions) conforms to 'the architecture'. I'm sympathetic to  
> that question... and at present I don't have an answer... do you....  
> or maybe you don't think it's a relevant question.

You (and/or Alan) ask: When does a deployment conform to 'the  
architecture'?

I'm quite satisfied if that question can be answered by referring to  
guidelines and best practices. I don't care at all if it can be  
objectively measured or not. Why would that matter?

Richard



>
>
>
> regards
>
> Stuart
>
> --
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Received on Friday, 8 February 2008 13:03:16 UTC