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Re: Recommendations for serving backlinks when having hash URIs?

From: Richard Cyganiak <richard@cyganiak.de>
Date: Wed, 10 Feb 2010 16:20:16 +0000
Cc: public-lod@w3.org
Message-Id: <7BD05A83-93F2-4F44-A036-555C54E40201@cyganiak.de>
To: nathan@webr3.org
Hi Nathan,

On 10 Feb 2010, at 13:57, Nathan wrote:
>> I'd recommend:
>>
>> <foo27#bar1> rdfs:seeAlso <slashland/foo27/bar1> .
>>
>> and then perform standard (non-redirect) content negotiation at
>> <slashland/foo27/bar1>, with variants at <bar1.rdf>, <bar1.html> etc.
>>
>
> Just wondering about the note on "non-redirect" content negotiation;  
> it
> was my understanding that you'd have to server the following HTTP  
> status
> codes under each scenario:
>
>  300 (Multiple Choices) if no Accept header is given.
>  303 (See Other) if an Accept header is given and a match is found.
>  406 (Not Acceptable) if an Accept header is not matched successfully.

Not quite.

See here for details on “normal” content negotiation:

http://www.w3.org/TR/cooluris/#conneg

About 300 and 406: A server *may* respond with 300 or 406 under the  
circumstances you describe above, but it *may* also just send a  
default representation back to the client. That's because the Accept  
header is just a statement of preference by the client, and it's up to  
the server wether it wants to consider those preferences.

About 303: You are conflating two things. Content negotiation is about  
serving *multiple* representations of a resource from a single URI.  
303 redirects are about resolvable URIs for things that have *no*  
representations because they exist outside of the Web. The 303  
redirect guides the client to a related document that describes the  
non-Web thing.

In Linked Data setups, those related documents at the destination of  
the 303 redirect often have multiple representations, and hence  
content negotiation enters the picture. This is described in Section  
4.2 of the document above. And actually, 303 and content negotiation  
are sometimes combined in just a single step, see Section 4.3 of that  
document. This is the setup that you see for example on DBpedia.

To see normal content negotiation in action, try requesting
http://httpd.apache.org/docs/2.1/logs.html
with different values for the "Accept-Language" header, e.g.
"en" -- you get English
"ja" -- you get Japanese
"de" -- you get English because it doesn't have German
"en,ja" -- you get English because the server decides so
no header -- you get English because the server decides so

Hope that clarifies things.

Best,
Richard



>
> what approach would you take under the "non-redirect" method? (details
> please)
>
> Many Regards,
>
> Nathan
Received on Wednesday, 10 February 2010 16:20:51 UTC

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