Re: Is 303 really necessary?

David, hello.

On 2010 Nov 8, at 09:40, David Booth wrote:

> On Sat, 2010-11-06 at 22:45 +0000, Norman Gray wrote:
> [ . . . ]
>> I take it that Ian is suggesting resolving the ambiguity he has
>> created, and thus the need for any heuristics, by extending the notion
>> of IR in such a way that a URI with a 200 response *is* an IR,
>> *unless* dereferencing it returns RDF which (authoritatively) declares
>> that the URI is a NIR.
> 
> I don't think that is feasible.  After all, what's so special about RDF?
> And how would the client even know whether RDF were returned?  Almost
> any serialization can be turned into RDF.  Suppose XML is returned.  Is
> that RDF?  A GRDDL transformation can cause it to be viewed as RDF?  And
> what about a plain HTML page?  Surely in that case the URI would
> identify the web page.  But what if there were some RDFa tags embedded?
> Suddenly it *doesn't* identify the web page?  Even if the client ignores
> those tags?

There's nothing fundamentally special about RDF, and if one ignores RDF, then the adjusted Decision is identical to the original one.

However, if W3C is going to pronounce on the semantics of the web, then it seems reasonable to allow W3C RDF some sort of privileged status -- "it's special because httpRange-14-bis says it's special!".

I appreciate that 'a URI...returns RDF' has the problem you identify.  However, is it really as uncertain as you describe?  In some circumstances, a server could prefer to return RDF over HTML, if that's at all compatible with the Accept header; and if an HTML resource includes RDFa or GRDDL, then it's clear that the resource owner intendes the derived RDF to be in some sense authoritative.

If a data consumer decides to turn XML into RDF, then the data owner can hardly be held responsible for the resulting RDF.

> No, I think it makes more sense to acknowledge that the ambiguity *has*
> been created by the server both returning the 200 response and sending a
> document saying that the URI identifies a toucan, but applications that
> are troubled by this ambiguity should use the provenance of the
> information to decide bits of information to use or ignore -- in this
> case ignoring the information given in the HTTP response code in favor
> of the information given in the RDF document.


I wouldn't claim there's zero ambiguity here.  However simply saying "httpRange-14 is defeasible" buys you some convenience.  If there are a few semi-standard practices about how that '</X> is a NIR' statement is discovered, then the remaining ambiguity is I would guess at least acceptable, and certainly lower than what is routinely tolerated in Linked Data applications generally.

Best wishes,

Norman


-- 
Norman Gray  :  http://nxg.me.uk

Received on Monday, 8 November 2010 15:52:14 UTC