  Grid technologies aim at enabling a coordinated resource-sharing and
problem-solving capabilities over local and wide area networks and span
locations, organizations, machine architectures and software boundaries. The
heterogeneity of involved resources and the need for interoperability among
different grid middlewares require the sharing of a common information model.
Abstractions of different flavors of resources and services and conceptual
schemas of domain specific entities require a collaboration effort in order to
enable a coherent information services cooperation.
  With this paper, we present the result of our experience in grid resources
and services modelling carried out within the Grid Laboratory Uniform
Environment (GLUE) effort, a joint US and EU High Energy Physics projects
collaboration towards grid interoperability. The first implementation-neutral
agreement on services such as batch computing and storage manager, resources
such as the hierarchy cluster, sub-cluster, host and the storage library are
presented. Design guidelines and operational results are depicted together with
open issues and future evolutions.
