RDF editor tools?

Hi,

Can anyone point me to free editing tool(s) for RDF or RDFS document
development ?
 (And are there any that provide graphical views?)

Thanks,
Margaret 

----
Margaret Lyell, Ph.D.
Principal Engineer, Distributed Systems
The MITRE Corporation
7515 Colshire Drive
McLean, VA 22102
--
703-883-6509 (phone)
mlyell@mitre.org