Relational abstraction in community-based secure collaboration

Users of an online community are willing to share resources because they can expect rea-sonable behaviour from other members of the community. Such expectations are known as social contracts. In this work, we study the specification and enforcement of social contracts in a computer mediated collaboration environment. Specifically, we examine social contracts that contain both relationship- and history-based elements. A series of policy languages, all based on modal and temporal logics, with increasing expressiveness, have been proposed to express social contracts. Reference monitors are designed to correctly and efficiently enforce the specified policies. A technique called “relational abstraction ” is employed to reduce the reference monitor into a purely relationship-based protection system, that is, what is commonly known as a social network system.