  We describe R-GMA (Relational Grid Monitoring Architecture) which has been
developed within the European DataGrid Project as a Grid Information and
Monitoring System. Is is based on the GMA from GGF, which is a simple
Consumer-Producer model. The special strength of this implementation comes from
the power of the relational model. We offer a global view of the information as
if each Virtual Organisation had one large relational database. We provide a
number of different Producer types with different characteristics; for example
some support streaming of information. We also provide combined
Consumer/Producers, which are able to combine information and republish it. At
the heart of the system is the mediator, which for any query is able to find
and connect to the best Producers for the job. We have developed components to
allow a measure of inter-working between MDS and R-GMA. We have used it both
for information about the grid (primarily to find out about what services are
available at any one time) and for application monitoring. R-GMA has been
deployed in various testbeds; we describe some preliminary results and
experiences of this deployment.
