  Resource sharing within Grid collaborations usually implies specific sharing
mechanisms at participating sites. Challenging policy issues can arise within
virtual organizations (VOs) that integrate participants and resources spanning
multiple physical institutions. Resource owners may wish to grant to one or
more VOs the right to use certain resources subject to local policy and service
level agreements, and each VO may then wish to use those resources subject to
VO policy. Thus, we must address the question of what usage policies (UPs)
should be considered for resource sharing in VOs. As a first step in addressing
this question, we develop and evaluate different UP scenarios within a
specialized context that mimics scientific Grids within which the resources to
be shared are computers. We also present a UP architecture and define roles and
functions for scheduling resources in such grid environments while satisfying
resource owner policies.
