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Review of Cool URIs for the Semantic Web

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Fri, 28 Mar 2008 13:39:52 -0400
Message-ID: <47ED2D68.90009@ibiblio.org>
To: public-sweo-ig@w3.org, Leo Sauermann <leo.sauermann@dfki.de>, Richard Cyganiak <richard@cyganiak.de>

Since I think this is quite an important note, I'm going to chime in.
While I do think there's problems with both 303s and hash URIs (Please
read this message to www-tag [1] to see how they both kinda have issues
from a purely Web standards viewpoint, or just read the entire paper at 
[2]), in certain cases they are better than nothing and I think it's the
job of this note to explain the TAG's decision, not change it :)

Minor semantic clarifications:

1) I kinda think, even though I think this is wrong, that the term
"information resource" applies to whatever might in some possible world
(i.e. the future) be returned over the Web. But if the TAG hasn't
noticed this then it doesn't likely matter, but just in case..

" In technical literature, such as Architecture of the World Wide Veb,
Volume One <http://www.w3.org/TR/2004/REC-webarch-20041215/> [AWWW
<http://www.w3.org/TR/cooluris/#ref-AWWW>], the term /Information
Resource/ is used instead of /Web document/." -> "For most purposes, in
technical literature like the Architecture of the World Wide Veb, Volume
One <http://www.w3.org/TR/2004/REC-webarch-20041215/> [AWWW
<http://www.w3.org/TR/cooluris/#ref-AWWW>], the term /Information
Resource/ can be considered synonymous with the term /Web document/."

2) Overall the document is excellent explanation. It would be better
also if it served as a bit of a primer, since after I've just been
indoctrinated into giving URIs to things by using 303s, an eager
developer might actually want to do this. Yet the example of how to
modify an .htaccess file so 303 and conneg can be used is  in "Best
Practice Recipes for Publishing RDF Vocabularies" [3].

Yet the only reference of this *extremely useful* cut and paste sort of
examples - precisely the kind needed by developers wanting to deploy
303s and conneg - is here  "The W3C's Semantic Web Best Practices and
Deployment Working Group has published a document that describes how to
implement the solutions presented here on the Apache Web server. The
Best Practice Recipes for Publishing RDF Vocabularies
<http://www.w3.org/TR/2006/WD-swbp-vocab-pub-20060314/> [Recipes
<http://www.w3.org/TR/cooluris/#ref-Recipes>] mostly discuss the
publication of /RDF vocabularies/, but the ideas can also be applied to
other kinds of small RDF datasets that are published from static files."
So, why not just either merge the documents? Or keep the "Cool URI"
document as an explanation, and keep technical examples in the Best
Practice Recipe Doc?

To make this document useful as a primer, you either you need to provide
working code (like .htaccess files) for your examples inline in the
document or *clearly* tell the readers this sort of thing is in the
"Best Practices" document.

To make your life easier, I'd just move all the rather technical details
in Sec 4.7 to the "Best Practice Recipes" in order to keep readers in
line. And say, "If you're going to need help implementing content
negotation and 303 redirection, please see the working examples for
modifying your server in Best Practice Recipes for Publishing RDF
Vocabularies <http://www.w3.org/TR/2006/WD-swbp-vocab-pub-20060314/>."

3) Remove mention of XRIs:

"*XRI <http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=xri>*
defines a scheme and resolution protocol for abstract identifiers. The
idea is to use URIs that contain wildcards, to adapt to changes of
organizations, servers, etc.
Examples are |@Jones.and.Company/(+phone.number)| or
|xri://northgate.library.example.com/(urn:isbn:0-395-36341-1)|."

XRIs are patented and not clearly royalty-free and IMHO can be dangerous
to use.  Either this should be mentioned or they should just be removed
entirely. I'd prefer to remove them entirely, since if one can't say
anything nice one should say nothing at all.  Or you could say "Using a
new scheme that isn't clearly in the public domain like the patented
technology of XRIs, could inadvertently put you in a sitution where a
company may demand money from you!"

Minor sentence clarifications:

"The notion of resource /identity/ was not so important on the
traditional Web, a URL simply identified whatever we see when we type it
into a browser"-> "The identity of a resource is not as important
outside the Semantic Web, since a URL simply identified whatever
web-page was accessed when we typed the URL into a browser."

"Has the homepage an email address? And why has the homepage a homepage?
" -> "Can a homepage itself have an e-mail address? And does it even
make sense for a home-page to have itself as its home-page?"

Maybe add a sentence or two: "A human can easily disambiguate these sort
of distinctions to tell apart Alice and her homepage. Yet on a Web where
data integration is performed automatically by computer programs, the
sort of ambiguity caused by a having a person and their homepage have
the same identifier can not be resolved automatically and may even cause
problems."

"a different setup is needed when publishing URIs that are meant to
identify entities." -> "but a different setup is needed when publishing
URIs that are meant to identify entities."

"In those cases the RDF data is extracted from the returned HTML
document." -> "In those cases the RDF data is extracted from the
returned HTML or XML document, and a new URI can be given to this
extracted data as needed."

This is actually quite complicated in GRDDL [4], but referencing this
might just be too scary for most people. Luckily, implementations just
do it.

The bottom URIs in this picture seem off,
http://www.w3.org/TR/cooluris/img20080321/303conneg.png.
Shouldn't they be http://www.example.com/aboutalice.rdf or
http://www.example.com/about/alice.rdf. Otherwise, are all users on the
system like Bob also being given the same about.rdf?

"When using 303 URIs for an ontology, like FOAF, the network delay can
reduce a client's performance considerable." -> "When using 303 URIs for
an ontology, like FOAF, network delay can reduce a client's performance
considerably"

"An ideal case are RDF Schema vocabularies and OWL ontologies, where" ->
"The ideal case is RDF Schema vocabularies and OWL ontologies, where"

"of the new" -> just delete. Some rather old URI schemes, including
URNs, don't provide a resolution service. Also, might add a sentence to
the extent that "Using a resolution-scheme to resolve to a http URI is
usually unnecessary, as often a stable http URI itself would accomplish
the exact same purpose but with less overhead."

"We see that HTTP URIs are still used to identify the location where to
download more information." -> "In this way, HTTP URIs are still used to
identify the location where to download more information."

Overall, great job!

[1]http://lists.w3.org/Archives/Public/www-tag/2008Mar/0073.html
[2]http://www.ibiblio.org/hhalpin/homepage/publications/indefenseofambiguity.html
[3]http://www.w3.org/TR/swbp-vocab-pub/
[4] http://www.w3.org/2004/01/rdxh/spec#base_misc
-- 

		-harry

Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Friday, 28 March 2008 17:40:32 GMT

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