Tripathi, AnandAhmed, TanvirKumar, RichaJaman, Shremattie2020-09-022020-09-022001-11-20https://hdl.handle.net/11299/215484We present here the execution model of a policy-drivenmiddleware for building secure distributed collaboration systems from their high level specifications. Our specification model supports nested collaboration activities and uses role based security policies and event count based coordination specification. From the specifications of a collaboration environment, appropriate policy modules are derived for enforcing security and coordination requirements. A policy-driven distributed middleware provides services to the users to join roles in an activity, perform role specific operations, or create new activities. We describe here the design challenges for the middleware and present the runtime structures and protocols supported by it for creating activities, roles, and objects. Our design takes into consideration that only some designated nodes can be trusted to enforce the required security policies for an activity.en-USReport