  We describe R-GMA (Relational Grid Monitoring Architecture) which is being
developed within the European DataGrid Project as an 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 VO 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 to do the job. We are able to invoke MDS info-provider scripts and
publish the resulting information via R-GMA in addition to having some of our
own sensors. APIs are available which allow the user to deploy monitoring and
information services for any application that may be needed in the future. We
have used it both for information about the grid (primarily to find what
services are available at any one time) and for application monitoring. R-GMA
has been deployed in Grid testbeds, we describe the results and experiences of
this deployment.
