[Mulgara-dev] descriptors/references

[David Wood]

Hi Bill,

On 7 Jul2007, at 01:05, William Mills wrote:
> So the major difference between rdf and mulgara that I have found  
> so far is
>
> That http://www.w3.org/1999/02/22-rdf-syntax-ns is actually  
> available as an XML reference document, and http://mulgara.org/ 
> mulgara is not.  Should this be true?

It depends and is under active discussion, especially within the W3C  
Technical Architecture Group.  At issue is whether HTTP URIs may  
refer to things that are not information resources (such as physical  
resources or namespaces) and whether the term "information resource"  
includes virtual concepts like namespaces at all.  This discussion is  
complicated by the fact that "information resources" are currently  
defined as things you get back from a URI dereferencing when the  
server responds with a 2XX HTTP response code (!).  It is all very  
circular.

The current state of thinking is that HTTP should return different  
status codes depending on what you are trying to do.  This should  
eventually result in a clean handling of both information and non- 
information resources by HTTP (and hopefully encourage everyone,  
including Mulgara) to ground their namespaces in URIs.

In brief, an HTTP 2XX return code should result when the transaction  
returns an information resource.  Non-information resources should  
result in an HTTP 303 (See Other) response, which may optionally list  
one or more URIs that relate to the non-informational resource (but  
are not in fact the resource itself).

Brian Sletten of the Mulgara community and I are actively upgrading  
the Persistent URL or PURL service at http://purl.org to handle the  
full range of HTTP return codes for this purpose.  It is our hope  
that Mulgara will follow others in using PURLs for namespace  
dereferencing.

Here is the current W3C guidance, but note the large number of  
disagreements in the draft document:

Dereferencing HTTP URIs
Draft TAG Finding 31 May 2007
http://www.w3.org/2001/tag/doc/httpRange-14/2007-05-31/HttpRange-14

and the older open TAG issue that started this discussion:
http://www.w3.org/2001/tag/issues.html#httpRange-14

Regards,
Dave