There are (at least) two modules you'll want to look at. One is CCK
and another is hier
http://cvs.drupal.org/viewcvs/drupal/contributions/sandbox/vauxia/hier/
which comes out of vauxia's experience with Operon
OK. Thank you very much for your quick answer. What I see from your links is that : - Those modules seem to be far from being released - None of them explicitly deals with RDF For the second point, is it that RDF approach has been tried but proved to be a dead-end ? Or is it just that it's not been tried ? Because standard-based approach is really a key *feature* for us : we want to be able to use all the tools that deal with with standard RDF. -- Sébastien Arbogast Blog : http://www.sebastien-arbogast.com The Epseelon Project : http://www.epseelon.org Projet Phénix : http://phenix.netbios.fr