Designing RDF data models

Hello all!
design of RDF data  models directly in RDF/XML is not an easy job, mainly
for beginners as me. It seems evident that graphical modelling tools could
well support RDF data model specifications. Some alpha released prototypes
are available in the RDF community, but they require still relevant
implementation effort, to be conveniently used in an application project.
Does someone suggest me some more stable design tool?
Thanks!
Giuseppe Bux