W3C home > Mailing lists > Public > www-tag@w3.org > March 2010

Re: 204 No Content for a resource which is known but has no representation yet?

From: Nathan <nathan@webr3.org>
Date: Mon, 15 Mar 2010 01:03:19 +0000
Message-ID: <4B9D8757.5020703@webr3.org>
To: "Roy T. Fielding" <fielding@gbiv.com>
CC: www-tag@w3.org, ietf-http-wg@w3.org
Roy T. Fielding wrote:
> On Mar 14, 2010, at 10:17 AM, Nathan wrote:
> 
>> Here is the full problem and solution I'd like to use:
>>
>> I'm stuck with Linked Data, which is tied to the http scheme
> 
> No, it isn't, unless you mean the data you happen to be using
> is only identified by http scheme URIs.
> 
>> and
>> has a constraint that the http scheme URIs we use as identifiers must be
>> dereferenced via http.
> 
> Are you making this up?  No known system that I am aware
> of has that limitation.

I think I worded it wrong, duly noted - I was referring to the case
where data is only identified using http scheme URIs and the assumption
that I should/must provide lookup (at this time) via dereferencing using
an http get, primarily because nobody else is talking about another way
of looking up those identifiers (that I am aware of).

>> The only way is forwards from what I can tell.
>>
>> As I see it (within the http scheme of uris), a resource is a conceptual
>> map to anything; that anything either has a representation that can be
>> sent via http or does not. In the case where it does not, the concept
>> maps to an "empty set" of representations.
> 
> Not really, no.  HTTP provides an interface for interacting with
> resources by way of making a request with a standard method upon
> a request-target that is a URI (with various parts scattered about
> for historical reasons).  HTTP provides that interface for URIs
> of any scheme.  Naturally, the native "http" scheme is most popular
> for this purpose because it maximizes the HTTP interface without
> requiring additional name services beyond hostname resolution (DNS).
> 
> The GET method, when applied to any resource, means get me a
> current representation of the identified resource.  HTTP doesn't
> need to say how it is possible for the server to know or obtain
> such a representation -- it simply does or does not do so.

noted and thanks for clarifying; I'd made that mental mistake of binding
HTTP to the http scheme.

>> With regards the above this calls for the usage of only 4 http status
>> codes (from what I can tell, certainly I could get by with them), as
>> follows:
>>
>> 204 No Content (in the case of GET), resource which maps to an empty set
>> / does not have a representation of its own that can be transferred by
>> the server over HTTP and no other resource is known which describes the
>> requested resource.
> 
> No, 204 means no content is the reply.  It is never used with GET.
> 404 means there is no current representation (i.e., not found).

that wipes out that option then! is there even such a thing as found but
with no description? i feel there is but now questioning. somebody else
suggested a 303 which resolves to a 404 - would that work?

>> 301 Moved Permanently, The requested resource has been assigned a new
>> permanent URI and any future references to this resource SHOULD use one
>> of the returned URIs.  Clients with link editing capabilities ought to
>> automatically re-link references to the request-target to one or more of
>> the new references returned by the server
>>
>> 303 See Other, indicates that the requested resource does not have a
>> representation of its own that can be transferred by the server over
>> HTTP, and additionally specifies a resource which may provide
>> information about the requested resource.
> 
> Yes, when used in response to GET.
> 
>> 410 Gone, The requested resource is no longer available at the server
>> and no forwarding address is known.  This condition is expected to be
>> considered permanent.  Clients with link editing capabilities SHOULD
>> delete references to the request-target after user approval.
>>
>> All of these codes are there already and do the job perfectly (imho),
>> and the others do not matter with regards linked data since we aren't
>> dealing with things which have a representation / entity.
> 
> Well, then you aren't using linked data.  I don't know what you
> are doing, but it is almost certainly wrong to say that data has
> no representation, and the whole point of linked data is to
> link the data via representations.

agreed, really I just want a way to "reserve" a resource/uri unambiguously.

>> additionally, it may be worth noting that I'm not doing any "content
>> negotiation" with a 303 See Other, rather I'm doing any required content
>> negotiation on the second resource, the one pointed do by the Location
>> header; personally I find it cleaner to keep a distinction between
>> resources with a representation and those without, and view content
>> negotiation in response to a request on a resource with no
>> representation as a cross cutting concern, hence dually seperated.
> 
> Agreed.
> 
>> I am aware this would be a refinement to the resolution of httpRange-14,
>> have done vast amounts of research on this (more than I expected) and in
>> reality I'm just a developer who is blocked on a project and I just need
>> some kind person from IETF/W3C (pref TAG) to say this doesn't conflict
>> with the architecture of the world wide web or conflict with HTTP/REST.
>>
>> Which means, somebody like Larry, or Roy, Tim etc; or even Jonathan Rees
>> as this very much ties in with the work on
>> http://www.w3.org/2001/tag/awwsw/http-semantics-report.html
> 
> Good luck with that.  The semantics report postulates a theory
> of existence for resources that simply does not matter to HTTP,
> and hence will be irrelevant to any real system you might build
> using HTTP aside from a closed-world graph theorem prover.
> 
> Even the REST notion of a discontinuous conceptual mapping function,
> which says exactly the same thing as the "correspondences"
> discussion in only four words, is merely an attempt to explain
> reality to a formalist, not make a formal restriction on reality.
> 
>> I'm really stuck here, and it's having real effects on my daily
>> life at home - I need to get this project finished and the above is the
>> only realistic solution after all my hunting; I'm trying so hard to do
>> things by the book  :(
> 
> Implement it first, using what works, and then tell the TAG
> what the theory should be.
> 
> Cheers,
> 
> Roy T. Fielding                            <http://roy.gbiv.com/>
> Chief Scientist, Day Software              <http://www.day.com/>

Thanks Roy, will try and get something working properly; facing many
challenges and hence all the feedback requests.

as a side note; does anybody have any suggestions for looking up data
with something like tdb uris? if there is a better way than just using
http scheme to dereference, even to be used in addition to http scheme
uri's, I'd be most interested - obviously keen not to have all the data
I ever produce bound to http scheme uri's only for looking up to get
more info etc.

Many Regards,

Nathan
Received on Monday, 15 March 2010 01:04:07 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 26 April 2012 12:48:20 GMT