  In "Grids" and "collaboratories," we find distributed communities of resource
providers and resource consumers, within which often complex and dynamic
policies govern who can use which resources for which purpose. We propose a new
approach to the representation, maintenance, and enforcement of such policies
that provides a scalable mechanism for specifying and enforcing these policies.
Our approach allows resource providers to delegate some of the authority for
maintaining fine-grained access control policies to communities, while still
maintaining ultimate control over their resources. We also describe a prototype
implementation of this approach and an application in a data management
context.
