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Re: A question - use 301 instead of 406?

From: Richard Cyganiak <richard@cyganiak.de>
Date: Fri, 26 Mar 2010 13:22:53 +0000
Cc: Linking Open Data <public-lod@w3.org>
Message-Id: <C6028B54-DAF6-4A4D-BC3A-9B14F767868E@cyganiak.de>
To: Hugh Glaser <hg@ecs.soton.ac.uk>
Hi Hugh,

Thinking more about this, I'm resetting to the start of the thread and  
I have a question for you.

The Cool URIs for the Semantic Web document, which is perhaps the  
canonical reference for the 303/conneg style of linked data  
publishing, lists two different design patterns for using 303  
redirects with slash URIs:

1. 303 URIs forwarding to One Generic Document
http://www.w3.org/TR/cooluris/#r303gendocument

2. 303 URIs forwarding to Different Documents
http://www.w3.org/TR/cooluris/#r303uri

AFAIK, RKBexplorer, like DBpedia and many other linked data sites,  
implement the second approach. When we tried to get the document  
through the TAG, TimBL insisted that the first approach is better and  
should come first in the Cool URIs document. So we did that. But the  
second approach was already deployed and has captured most of the  
mindshare and still is the default today, and the first approach has  
never really caught on.

My question for you: Does the first approach solve your problem? By  
always 303ing to a generic document, you'd see a document URL in the  
browser bar that could respond with either HTML or RDF. The variant- 
specific URIs would still be there but not be used in typical HTTP  
interactions. Does this solve the issue that motivated you here?

Best,
Richard


On 23 Mar 2010, at 22:50, Hugh Glaser wrote:

> I am not sure I even dare ask this, but here goes.
> (This is prompted by a real application implementation - it is not  
> just a
> hypothetical.)
>
> Assuming that we are in the usual situation of http://foo/bar doing  
> a 303 to
> http://foo/bar.rdf when it gets a Accept: application/rdf+xml http://foo/bar
> what should a server do when it gets a request for
> Accept: application/rdf+xml http://foo/bar.html ?
>
> OK, the answer is 406.
>
> But is this compatible with the principle of being as forgiving as  
> possible
> as a server?
>
> I think it is clear what the agent wanted:
> Accept: application/rdf+xml http://foo/bar
> it is just that somehow the wrong URI got into the system.
>
> I know I have made the mistake of for example copying a dbpedia URI  
> from the
> address bar when I was looking for the LD URI, and ended up  
> wondering for a
> moment why
> Accept: application/rdf+xml http://dbpedia.org/page/Tim_Berners-Lee
> gives me a 406 before I remember I need to right click on the About  
> and copy
> the link.
>
> That's OK if all that happens is I use the wrong URI straight away.
> But what happens if I then enter it into a form that requires a LD  
> URI, and
> then perhaps goes into a DB, and becomes a small part of a later  
> process?
> Simply put, the process will fail maybe years later, and the  
> possibility and
> knowledge to fix it will be long gone.
>
> Maybe the form validation is substandard, but I can see this as a  
> situation
> that will recur a lot, because the root cause is that the address  
> bar URI
> changes from the NIR URI. And most html pages do not have links to  
> the NIR
> of the page you are on - I am even told that it is bad practice to  
> make the
> main label of the page a link to itself - wikipedia certainly doesn't,
> although it is available as the "article" tab, which is not the  
> normal thing
> of a page. SO in a world where wikipedia itself became LD, it would  
> not be
> clear to someone who wanted the NIR URI where to find it.
>
> So that is some of the context and motivation.
> If we were to decide to be more forgiving, what might be done?
> How about using 301?
> <<Ducks>>
> To save you looking it up, I have appended the RFC2616 section to this
> email.
> That is
> Accept: application/rdf+xml http://foo/bar.html
> Should 301 to http://foo/bar
> It seems to me that it is basically doing what is required - it  
> gives the
> client the expected access, while telling it (if it wants to hear)  
> that it
> should correct the mistake.
> One worry (as Danius Michaelides pointed out to me) is that the  
> caching may
> need careful consideration - should the response indicate that it is  
> not
> cacheable, or is that not necessary?
>
> So that's about it.
> I am unhappy that users doing the obvious thing might get frustrated  
> trying
> to find the URIs for heir Things, so really want a solution that is  
> not just
> 406.
> Are there other ways of being nice to users, without putting a serious
> burden on the client software?
>
> I look forward to the usual helpful and thoughtful responses!
>
> By the way, I see no need to 301 to http:/foo/bar if you get a
> Accept: text/html http://foo/bar.rdf as the steps to that might lead  
> to this
> would require someone looking at an rdf document to decide to use it  
> as a
> NIR, which is much less likely. And the likelihood is that there is an
> eyeball there to see the problem.
> But maybe it should?
>
> Best
> Hugh
>
>
> 10.3.2 301 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-URI to one or more of the new
>   references returned by the server, where possible. This response is
>   cacheable unless indicated otherwise.
>
>   The new permanent URI SHOULD be given by the Location field in the
>   response. Unless the request method was HEAD, the entity of the
>   response SHOULD contain a short hypertext note with a hyperlink to
>   the new URI(s).
>
>   If the 301 status code is received in response to a request other
>   than GET or HEAD, the user agent MUST NOT automatically redirect the
>   request unless it can be confirmed by the user, since this might
>   change the conditions under which the request was issued.
>
>      Note: When automatically redirecting a POST request after
>      receiving a 301 status code, some existing HTTP/1.0 user agents
>      will erroneously change it into a GET request.
>
>
Received on Friday, 26 March 2010 13:23:28 UTC

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