- From: Nathan <nathan@webr3.org>
- Date: Wed, 28 Mar 2012 16:07:17 +0100
- To: Jeni Tennison <jeni@jenitennison.com>
- CC: public-lod@w3.org, "www-tag@w3.org List" <www-tag@w3.org>
Jeni Tennison wrote: > Nathan, > > Yes, that's correct. With no constraining Accept headers, it could alternatively return HTML with embedded RDFa with a <link rel="describedby"> element, for example. Is that universally true? Suppose /uri identified a PDF formatted ebook, or a digital image of a monkey in JPEG format, or even an RDF document. Question A: Currently we have: <http://example.org/uri> - a JPEG image of a monkey. When you issue a GET on that URI the server currently responds 200 OK Content-Type: image/jpeg Link: <http://example.org/uri-documentation>; rel="describedby" So under this new proposal, the server can return the contents of /uri-documentation with a status of 200 OK for a GET on /uri? If yes, this seems like massively unexpected functionality, like a proposal to treat "Accept: some/meta-data" like a DESCRIBE verb, and seems to exaggerate the URI substitution problem (as in /uri would be taking as naming the representation of /uri-documentation). If no, where's the language which precludes this? (and how would that language go, given that it's exactly the same protocol flow and nothing has changed - other than the reader presuming that /uri now identifies something that does have a representation that can be transferred over HTTP vs identifying something that doesn't have a representation that can be transferred over HTTP). Question B: How would conneg work, and what would the presence of a Content-Location response header mean? Would HTTPBis need to be updated? Question C: Currently 303 "indicates that the requested resource does not have a representation of its own that can be transferred by the server over HTTP", and the Link header makes it clear that you are dealing with two different things (/uri and /uri-documentation), but where does this proposal make it clear at transfer protocol level that the representation included in the http response is a representation of another resource which describes the requested resource (rather than it being as the spec defines "a representation of the target resource")? > Either way, there is no implication that what you've got from http://example.org/uri is the content of http://example.org/uri (or that http://example.org/uri identifies an information resource), but there is an implication that what you get from http://example.org/uri-documentation is the content of http://example.org/uri-documentation (and that http://example.org/uri-documentation is an information resource). Sorry I don't follow, how is there an implication from a 200 OK for <uri-a> that it's not an IR and for <uri-b> that it is an IR? If there was a Set of all Things (Set-A), then that set would have two sets, "the set of all things which can be transferred via a transfer protocol like HTTP" (Set-B), and then everything else (Set-C) which comprises Set-A minus Set-B. As far as I can tell, the one thing that determines whether something is a member of the Set-B or Set-C, for HTTP, is that 200 OK in response to a GET, hence why we need the 303. This proposal appears to try and override that "rule" (fact) by saying let the content of a representation define what is a member of Set-B or Set-C, however the act of dereferencing itself is what determines whether an identified thing is a member of Set-B, as Set-B is the set of all things that can be dereferenced. Hence my confusion at this proposal. Hope that makes sense, and that I've not totally misunderstood. Best, > Jeni > > On 28 Mar 2012, at 14:46, Nathan wrote: > >> Nathan wrote: >>> Jeni Tennison wrote: >>>> # Details >>>> >>>> In section 4.1, in place of the second paragraph and following list, substitute: >>>> >>>> There are three ways to locate a URI documentation link in an HTTP response: >>>> >>>> * using the Location: response header of a 303 See Other response [httpbis-2], e.g. >>>> >>>> 303 See Other >>>> Location: http://example.com/uri-documentation> >>>> >>>> * using a Link: response header with link relation 'describedby' ([rfc5988], [powder]), e.g. >>>> >>>> 200 OK >>>> Link: <http://example.com/uri-documentation>; rel="describedby" >>>> >>>> * using a ‘describedby’ ([powder]) relationship within the RDF graph created by interpreting the content of a 200 response, eg: >>>> >>>> 200 OK >>>> Content-Type: text/turtle >>>> >>>> PREFIX :<http://www.iana.org/assignments/relation/> >>>> <http://example.com> :describedby <http://example.com/uri-documentation> ; >>>> . >>>> >>> Seeking clarification, >>> Given some arbitrary thing and a description of that thing, let's say: >>> <http://example.org/uri> is described by <http://example.org/uri-documentation> >>> Previously we could GET /uri and either: >>> a) follow the value of the Location header in a 303 response to get to /uri-documentation >>> b) follow the value of the Link header to get to /uri-documentation >>> With this proposal though we'd be able to say issue a GET to /uri with an Accept header value of text/turtle, and the server could return back the contents of /uri-documentation, with a status of 200 OK, and where the text/turtle response contained: >>> PREFIX :<http://www.iana.org/assignments/relation/> >>> <http://example.com> :describedby <http://example.com/uri-documentation> >> PREFIX :<http://www.iana.org/assignments/relation/> >> <http://example.org/uri> :describedby <http://example.org/uri-documentation> >> >> c+p error, apologies. >> >>> Is this correct? >>> TIA >> >> >
Received on Wednesday, 28 March 2012 15:08:39 UTC