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Re: Important Change to HTTP semantics re. hashless URIs

From: Pat Hayes <phayes@ihmc.us>
Date: Sun, 24 Mar 2013 23:12:37 -0500
Cc: "public-lod@w3.org" <public-lod@w3.org>, "public-rww@w3.org" <public-rww@w3.org>, "public-webid@w3.org" <public-webid@w3.org>, "dbpedia-discussion@lists.sourceforge.net" <dbpedia-discussion@lists.sourceforge.net>
Message-Id: <8D55A8DC-6C6D-4819-A348-62B9196B001B@ihmc.us>
To: Kingsley Idehen <kidehen@openlinksw.com>

On Mar 24, 2013, at 12:39 PM, Kingsley Idehen 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).
> "
> 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:

I think not quite exactly as you describe it:

> 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 .

I think in fact all it can infer is

1. <http://dbpedia.org/resource/Barack_Obama> denotes an entity, and
2. <http://dbpedia.org/page/Barack_Obama> denotes the Web Document that describes that entity. 

You can't actually get referents from HTTP protocols: for that, you have actually read (and understand) the documents that specify the referents. 

Still, this is all excellent progress. 


> 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

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Received on Monday, 25 March 2013 04:13:17 UTC

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