Re: working around the identity crisis

On 14.11.2004 17:20:12, Miles, AJ (Alistair) wrote:
>Sorry, reposting this with a more sensible title - a discussion about
>working around the 'identity crisis' for http uris:

>Would very much like to know what folks think of this.  Have I just managed
>to redescribe some emerging consensus, have I misunderstood anything, should
>I go away and read more?
I like your work-around very much, so I dare to add my 2 cents:
IMHO there isn't really a URI identity crisis at all. we only run
into trouble when we start using a URI to identify two different
things. From an *RDF* point of view it would basically not even
hurt to serve a representation of a non-document resource at its
URI. But(!) the problem then is, that from a *human* (or automated
semweb agent) point of view, there is now a document served at that
URI and sooner or later  someone (incl. automated semweb agents)
could start asserting things about that document (lastModified
etc.), using the URL as a URI, and we are in a kind of crisis,
as RDF machinery would merge the descriptions. (following your
argumentation, we should better call the problem the "seth brundle"
and not a "URI identity" crisis.)

As you describe in the wiki page, the most important thing is to
keep non-document resource URIs distinct from potential documents
describing the resource in question. And you also provide a
practical approach that still allows serving additional information
via (not *at*) a resource's URI, therefore keeping a triple store's
data consistent. And patrick added that the way *how* you keep that
distinction is up to the implementor. I'd also say that the solution
you mention is a very implementation-friendly approach (and IMHO
better than "XSLT at the same location" which still uses the same
URI for the RDF/XML and the html). I invested some (too much AND
probably still not enough) time in reading about this whole
discussion, as I'm trying to use a similar mechanism for the new site. So far, I plan to use the http "303 see
other" redirect approach[1] described by (I think) sandro hawke,
in combination with content negotiation. A request for a non-document
individual such as "" with
an "Accept: application/rdf+xml" header would result in a 303 to
"", where then an
rdf/xml document would be available. An xhtml representation would be
served at another URL. For web-pages that are going to be
published at a fixed URL, I'm going to add <link .../> tags, and
perhaps an additional x-metadata-location header, which could
also be used with non-xml web resources such as images. This may
not be the best solution (URIQA's MGET is definitely based on a
cleaner and more efficient design, but I'm not able to implement
the server part of it), but it appeared to me to be one of the
most practical solutions until the SWBPD WG proposes some sort
of recommendation which addresses the "description vs.
representation" and "rdf discovery" issues. (Someone started a
survey a couple of weeks ago regarding rdf tools' support for
http accept headers. not sure if the results have already been
published somewhere, though.)



Benjamin Nowack

Kruppstr. 100
45145 Essen, Germany

@ DERI Galway from 2004-10-01 to 2004-12-02

>I wanted to say also that I am acutely aware that alot of people have spent
>a lot more time thinking and writing about this than I have.  I'm really
>just trying to understand this problem space, and get to a place were I can
>effectively explain the issue (and the options) to other people.
>Responding to Patrick:
>'If you have a URI that identifies a concept, and dereferencing that URI in
>a browser results in some web page displayed in that browser, that does not
>mean that the URI has been used to identify two things, the concept and
>the web page (document).'
>I think that puts very concisely the fundamental point I was trying to make.
>I probably didn't need to say any more than this.
>Responding to Daniel:
>'A good solution, but I still prefer the notion of using XSLT to
>transform the RDF/XML definition of a concept into a human friendly
>HTML page about it.'
>I agree that, as a matter of good practise, any alternate content-type
>representations of the same concept need to be synchronised.  One way of
>achieving this would be to use an RDF/XML description as the reference
>point, and using XSLT to generate an HTML representation.
>Alistair Miles
>Research Associate
>CCLRC - Rutherford Appleton Laboratory
>Building R1 Room 1.60
>Fermi Avenue
>Oxfordshire OX11 0QX
>United Kingdom
>Tel: +44 (0)1235 445440

Received on Monday, 15 November 2004 15:11:29 UTC