On Sun 2013-Mar-24, at 17:39, Kingsley Idehen <kide...@openlinksw.com> wrote:
> All, > > Here is a key HTTP enhancement from Hypertext Transfer Protocol (HTTP/1.1): > Semantics and Content note from IETF [1]. > > " > 4. If the response has a Content-Location header field and its > field-value is a reference to a URI different from the effective > request URI, then the sender asserts that the payload is a > representation of the resource identified by the Content-Location > field-value. However, such an assertion cannot be trusted unless > it can be verified by other means (not defined by HTTP). > " > It's good to have the clarification (the wording in the new draft is nicer), but it's probably worth stressing that Content-Location isn't at all new, and this *mostly* amounts to a tidying-up of wording rather than a change in semantics. Section 14.14 of RFC2616 (HTTP/1.1) states: “The Content-Location entity-header field MAY be used to supply the resource location for the entity enclosed in the message when that entity is accessible from a location separate from the requested resource's URI." The biggest change here is actually the “However, such an assertion cannot be trusted..." part! M. > > Implications: > > This means that when hashless (aka. slash) HTTP URIs are used to denote > entities, a client can use value from the Content-Location response header to > distinguish a URI that denote an Entity Description Document (Descriptor) > distinct from the URI of the Entity Described by said document. Thus, if a > client de-references the URI <http://dbpedia.org/resource/Barack_Obama> and > it gets a 200 OK from the server combined with > <http://dbpedia.org/page/Barack_Obama> in the Content-Location response > header, the client (user agent) can infer the following: > > 1. <http://dbpedia.org/resource/Barack_Obama> denotes the real-world entity > 'Barack Obama' . > 2. <http://dbpedia.org/page/Barack_Obama> denotes the Web Document that > describes real-world entity 'Barack Obama' -- by virtue of the fact that the > server has explicitly *identified* said resource via the Content-Location > header . > > Basically, the Toucan Affair [2][3][4] has now been incorporated into HTTP > thereby providing an alternative to 303 redirection which has > troubled/challenged many folks trying to exploit Linked Data via hashless > HTTP URIs. > > Implementations: > > As per my comments in the Toucan Affair thread, our ODE [5] Linked Data > client has always supported this heuristic. In addition, I am going propose > implementing this heuristic in DBpedia which will simply have the net effect > of not sending a 303 to user agents that look-up URIs in this particular > Linked Data space. > > Linked Data Client implementation suggestions: > > I encourage clients to support this heuristic in addition to 303 with regards > to Linked Data URI disambiguation. Implementation costs are minimal while the > upside extremely high re., Linked Data comprehension, appreciation, and > adoption. > > Links: > > 1. http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-22#page-15 . > 2. http://blog.iandavis.com/2010/11/04/is-303-really-necessary/ -- Is 303 > Really Necessary post by Ian Davis. > 3. http://lists.w3.org/Archives/Public/public-lod/2010Nov/0090.html -- > mailing list thread . > 4. > http://linkeddata.uriburner.com/about/html/http/iandavis.com/2010/303/toucan > -- example of heuristic handling . > 5. http://ode.openlinksw.com -- ODE Linked Data consumer service, > bookmarklets, and cross-browser extensions. > 6. http://bit.ly/YxW21k -- Illustrating Semiotic Triangle using DBpedia's > Linked Data URIs . > > -- > > Regards, > > Kingsley Idehen > Founder & CEO > OpenLink Software > Company Web: http://www.openlinksw.com > Personal Weblog: http://www.openlinksw.com/blog/~kidehen > Twitter/Identi.ca handle: @kidehen > Google+ Profile: https://plus.google.com/112399767740508618350/about > LinkedIn Profile: http://www.linkedin.com/in/kidehen > > > > > -- Mo McRoberts - Analyst - BBC Archive Development, Zone 1.08, BBC Scotland, 40 Pacific Quay, Glasgow G51 1DA, MC3 D4, Media Centre, 201 Wood Lane, London W12 7TQ, 0141 422 6036 (Internal: 01-26036) - PGP key CEBCF03E ----------------------------- http://www.bbc.co.uk This e-mail (and any attachments) is confidential and may contain personal views which are not the views of the BBC unless specifically stated. If you have received it in error, please delete it from your system. Do not use, copy or disclose the information in any way nor act in reliance on it and notify the sender immediately. Please note that the BBC monitors e-mails sent or received. Further communication will signify your consent to this. -----------------------------
