In message <[log in to unmask]>, Paul Walk 
<[log in to unmask]> writes
>
>However, I've always been a little unconvinced by the 'Cool URIs don't 
>change' piece (http://www.w3.org/Provider/Style/URI) linked to by the 
>W3C Note you referenced. While I agree with the sentiment, I think the 
>W3C statement does not quite gel with my practical experience.
>
>The gluing together of the object identifier with the organisational 
>domain part of a URL is seen by some as a potential problem, and is 
>addressed for example in John Kunze's paper on ARK 
>(http://colab.mpdl.mpg.de/mediawiki/images/e/eb/ESci08_Sem_1_n2t_a_viabl
>e_pid_solution_Kunze.pdf )
>
>The W3C would maintain that this is unnecessary. I tend to lean 
>towards the W3C in this respect - but really because I think the 
>deleterious effect of changing URIs can be overstated, so it's not 
>necessarily worth introducing another layer of complexity.

Paul,

Your comments on feasibility are well taken, but I think that in the 
particular context of the Semantic Web, stable URIs are pretty central 
to whether the whole thing will work at all.  This isn't just related to 
whether they resolve to a physical resource (the point John Kunze 
discusses in the presentation you quote): not so long ago the same job 
was to be done by "URNs", which didn't (and in fact couldn't) point to 
anything.

The other, crucial, job that stable URIs do is that they become a common 
currency, expressing a well-defined class or property.  People use them 
in their own RDF, and the magic of Semantic Web data linking starts to 
happen. If your RDF instances are just strings (rather than rdf:about 
links), it's effectively just a local resource.  Ditto if all your 
rdf:about links just point to somewhere else in your own data set.

The above comments are based on my own experiments in this area, and may 
well be misguided or plain wrong.  If so, I would be delighted to be put 
right.  Meanwhile, let me explain what I have been up to since the last 
message in this thread ...

Just to see what is involved in implementing the W3C advice on Cool 
URIs, Open Data, etc., I have built a front end to the Wordsworth Trust 
to expose their collection as RDF.  While this is very much a work in 
progress, it has got to the point where there is something to see.

The whole thing is built on the basis that none of the resources 
identified by the URLs actually exist (!) ... in other words the 
redirection work is all done by a customized "404 page not found" error 
handler.  (Since the server in question is IIS, this is an Active Server 
Page.)  The object URLs all have the form:

http://collections.wordsworth.org.uk/object/[identity number]

e.g.
http://collections.wordsworth.org.uk/object/GRMDC.C104.15

If you request this URL in a normal web context, you are redirected to 
the object's page on the standard site (try it).  If your HTTP request 
includes the header "Accept: application/rdf+xml", it will instead issue 
a "303 See Also" response, and give the URL which delivers RDF:

http://collections.wordsworth.org.uk/object/data/GRMDC.C104.15

You can request this in your browser, and if you have something like the 
RDF Tabulator extension to Firefox, you can see it as a nicely rendered 
table of properties and values.  Otherwise you'll get an RDF XML dump - 
always a pleasure ;-)  (BTW, I don't get anything using IE - maybe I'm 
not setting the MIME type properly.)  You can also open it in the RDF 
browser provided by OpenLink:

http://demo.openlinksw.com/DAV/JS/rdfbrowser/index.html

Once it's loaded some triples, click on the "Raw triples" tab to see 
them.

Within my transform, I look up the most specific place name in Geonames, 
and if I get a good match I include the Geonames URL in place of the 
keyword.  If you follow the "data link" after the Geonames URL, this 
loads information about the place, and then you can switch to the "Yahoo 
Map" tab and see it as the familiar pin on a map.  Load a few of the 
C104 series in the same way, and you can see the distribution of this 
set of prints - all without doing extra work on the catalogue record. 
Similarly, by using the W3C Calendar namespace 
(http://www.w3.org/2002/12/cal/icaltzd) for my dates, I get entries on 
the timeline.

The RDF is produced by an XSLT transform on the live source record 
(which is already XML).  At present it almost totally fails to meet my 
criterion for successful Open Linking, but does raise some interesting 
issues:

1. The properties I use are mostly taken from DBpedia.  They are 
effectively what has been scraped from Wikipedia.  Should the museum 
community be publishing an ontology of properties that it is interested 
in?

2. Are we interested in finding or creating ontologies for common stuff 
like object type ("simple name") and materials?

3. How do we deal with the biggies? - people are the obvious one.

In general, the main conclusion I have drawn from this exercise is that 
if we are to contribute to, and benefit from, this initiative, we need 
to look way outside our own little community of practice.

Thanks for reading if you got this far ...

Richard
-- 
Richard Light
XML/XSLT and Museum Information Consultancy
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