[Om] Going real with the OpenMath CD Linked Data

Christoph LANGE ch.lange at jacobs-university.de
Wed Jul 27 11:44:17 CEST 2011 

Hi Paul,

I'm back working on the linked data publication.

On 26/07/2011 13:12, Paul Libbrecht wrote:
> one version is active now. It was manually contributed by our sysadmin and worked for the xhtml case.
> Another version is coming up in a few minutes which is almost the
> same as your file.

Thanks, the redirects seem to work.  I have just tried "cdname" with
different Accept headers and it looks all fine.

BTW, contrary to the original .htaccess file that I sent you, I think
it would make sense to redirect requests to "cdname" without an Accept
header to the *.ocd files instead of *.xhtml.  That mainly addresses
users of command-line clients such as wget, and it would help to make
them aware of the original implementation of the CDs in the OCD
format.

> thanks for feedback
> There's an amount of URLs that need to be checked, including:
> - http://www.openmath.org/cd/cdname.xhtml
> - http://www.openmath.org/cd/cdname (with a diversity of accept
> headers)

these work

> - http://www.openmath.org/cd/cdname.html (historical)

That ultimately redirects to cdname.xhtml, as desired, but for some
strange reason the redirect goes via the intermediate step
cdname.html.xhtml (in case of "Accept: text/html") or via
cdname.html.rdf (if there is no Accept header):

--- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< ---

$ wget --header="Accept: text/html" -O /dev/null -S 
http://www.openmath.org/cd/a
lg1.html
--2011-07-27 11:33:57--  http://www.openmath.org/cd/alg1.html
Resolving www.openmath.org (www.openmath.org)... 134.96.184.220
Connecting to www.openmath.org (www.openmath.org)|134.96.184.220|:80... 
connecte
d.
HTTP request sent, awaiting response...
   HTTP/1.1 303 See Other
   Date: Wed, 27 Jul 2011 09:33:56 GMT
   Server: Apache/2.0.50 (Linux/SUSE)
   Location: http://www.openmath.org/cd/alg1.html.xhtml
   Content-Length: 337
   Keep-Alive: timeout=15, max=100
   Connection: Keep-Alive
   Content-Type: text/html; charset=iso-8859-1
Location: http://www.openmath.org/cd/alg1.html.xhtml [following]
--2011-07-27 11:33:58--  http://www.openmath.org/cd/alg1.html.xhtml
Reusing existing connection to www.openmath.org:80.
HTTP request sent, awaiting response...
   HTTP/1.1 301 Moved Permanently
   Date: Wed, 27 Jul 2011 09:33:56 GMT
   Server: Apache/2.0.50 (Linux/SUSE)
   Location: http://www.openmath.org/cd/alg1.xhtml
   Content-Length: 333
   Keep-Alive: timeout=15, max=99
   Connection: Keep-Alive
   Content-Type: text/html; charset=iso-8859-1
Location: http://www.openmath.org/cd/alg1.xhtml [following]
--2011-07-27 11:33:58--  http://www.openmath.org/cd/alg1.xhtml
Reusing existing connection to www.openmath.org:80.
HTTP request sent, awaiting response...
   HTTP/1.1 200 OK
   Date: Wed, 27 Jul 2011 09:33:56 GMT
   Server: Apache/2.0.50 (Linux/SUSE)
   Last-Modified: Mon, 25 Apr 2011 22:18:18 GMT
   ETag: "73daa-878e-95a39e80"
   Accept-Ranges: bytes
   Content-Length: 34702
   Keep-Alive: timeout=15, max=98
   Connection: Keep-Alive
   Content-Type: application/xhtml+xml
Length: 34702 (34K) [application/xhtml+xml]
Saving to: `/dev/null'

100%[======================================>] 34,702      --.-K/s   in 0.1s

2011-07-27 11:33:58 (319 KB/s) - `/dev/null' saved [34702/34702]

--- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< ---

> - http://www.openmath.org/cd/cdname.xml (historical)

That one does not yet work. BTW, what should *.xml redirect to? To
*.xhtml, or to *.ocd, or to *.rdf?  Note that all of these are XML
formats.

> Maybe we need to add more redirects.

> I am wondering if redirect (303 in your case) is the right thing to do.
> I believe it is ok to actually server the resource, which gives all the right headers, under
>    http://www.openmath.org/cd/cdname
> or?

For answering that I have to dig into linked data specifications.  The
short answer is that 303 redirects are part of the linked data best
practices, and that most linked data clients won't work otherwise.
One can test that in a very nice way using the
http://validator.linkeddata.org/vapour validator.

The long version, quoting from
http://www.w3.org/TR/cooluris/#r303gendocument

--- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< ---
… to use a special HTTP status code, 303 See Other, to give an 
indication that the requested resource is not a regular Web document. 
Web architecture tells you that for a thing resource (URI) it is 
inappropriate to return a 200 because there is, in fact, no suitable 
representation for those resources. However, it is useful to provide 
information about those resources. The W3C's Technical Architecture 
Group proposes in its httpRange-14 resolution [httpRange] document a 
solution that is to direct you to a document which has information about 
the thing you asked about. By doing this we avoid ambiguity between the 
original, real-world object and the resource that represents it.
--- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< --- %< ---

In short: The cdname.rdf RDF/XML file, which is the target of the
redirect, is not the same as "the 'cdname' OpenMath CD". E.g. the
cdname.rdf file may have metadata such as dc:creator = "Christoph
Lange", dc:date = "2011-07-27" (because I created it), whereas the
actual OpenMath CD, i.e. the thing described by the URI
<http://www.openmath.org/cd/cdname> (and not by the URI
<http://www.openmath.org/cd/cdname.rdf>) would rather have metadata
such as dc:creator = "James Davenport", dc:date = "2004-06-30".  For
our day-to-day practice this distinction is rather philosophical, but,
as I said above, linked data tools expect 303 redirects nevertheless.

> Robin Berjon had a particularly nice post here:
>     http://berjon.com/blog/2009/12/xmlbp-non-http-namespaces.html
> where he says... don't name the technology of your namespace document! Another day it's going to be another technology... I understand this as the fact that we should share URLs without the nitty gritty details that made us use .xml one day and .xhtml another day... just use one name and do the right thing (of today and in the future).

I completely agree with that, and I think that with the improved
redirects we achieved exactly that.

Cheers,

Christoph

-- 
Christoph Lange, Jacobs University Bremen
http://kwarc.info/clange, Skype duke4701

Workshop: Ontologies come of Age in the Semantic Web (OCAS)
Ontology User Experience Challenge (1st prize US$ 2000)
October 23 or 24 at the Intl. Semantic Web Conference, Bonn, Germany
Submission deadline August 15, http://ocas.mywikipaper.org

More information about the Om mailing list