Re: RSS 1.0 with Jena

I haven't got any usable code available, but have spent a fair bit of
time with RSS + Jena. A while ago I set up an RSS aggregator, the
approach (if I remember correctly) was something like this:

1. a Jena model is given the list of channel URIs (as rss:channel instances)
2.  a URI is chosen
3. an external HTTP client gets the RSS 
4. the RSS is fed through an XSLT stylesheet *
5. the result is loaded into the Jena Model
6. a statement is added to the model giving the current time as a
property of that rss:channel (along with any useful headers from the
HTTP client)
7. the rss:channel with the next oldest update time is chosen, goto 3.

* in 4 I used an XSLT stylesheet to convert RSS x.x to RSS 1.0. 
Morten Frederikson's done a good XSLT, see:
http://purl.org/net/syndication/subscribe/feed-rss1.0.xsl
(also, for channels:
 http://purl.org/net/syndication/subscribe/list-ocs0.5.xsl) 

For display you can either select data from the model programmatically
(a bit like DOM) or using RDQL queries. (for a 3-pane style view I did
the former, with the results going into a JTree-based component on the
left and a Swing HTML editor kit thingy area on the right).

If I was to do this again with Jena now, I'd probably use the Rome RSS
toolkit + Apache Commons HTTP Client for the feed front end rather
than XSLT, it /should/ be more versatile and robust with dodgy feeds.

The model can be file or RDBMS-backed (I just used file in prototypes,
though had planned to mode to a HSQL base to allow zero-config use).

For RSS 1.0 generation, you can simply build up a Jena model to
represent the feed adding statements as appropriate, either
programmatically or through RDQL inserts (I haven't tried the latter).
The biggest problem is with serializing the data in such a way that it
appears in the syntax that some aggregators expect. I didn't manage to
do this with Jena 1.6 but I believe the serializers in Jena 2 are a
lot more versatile and things like the default namespace can be set
(some aggregators don't even understand namespaces, so the rss: prefix
has to go). Ian Davis has recently been looking at strategies for
'normalising' RDF/XML to fit with rigid XML syntaxes, see:

 http://internetalchemy.org/2004/10/constraining-rdfxml

I think there's also potential for using XSLT for this kind of
filtering, it should be very straightforward if the source format is
predictable, like out of a standard RDF/XML serializer.

Cheers,
Danny.

On Wed, 13 Oct 2004 01:51:34 -0000, alexandre_martini
<alexandre_martini-/E1597aS9LRfJ/[email protected]> wrote:
> 
> 
> Hi,
> 
> Does anybody have developed anything addressing RSS using Jena?
> (http://sourceforge.net/projects/jena)
> 
> Thanks!
> 
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 


-- 

http://dannyayers.com


 
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