Access control is an indispensable part of any information sharing system. Collaborative environments introduce new requirements for access control, which cannot be met by using existing models developed for non-collaborative domains. We have developed a new access control model for meeting these requirements, The model is based on a generalized editing model of collaboration, which assumes that usersinteract with a collaborative application by concurrently editing its data structures, It associates fine-grained data displayed by a collaborative application with a set of collaboration rights and provides programmers and users a multi-dimensional, inheritance-based scheme for specifying theserights. The collaboration rights include traditional read and write rights and severat new rights such as viewing rights and coupling rights. The inheritance-based scheme groups subjects, protected objects, and access rights; allows each component of an access specification to refer to both groups and individual members; and allows a specific accessdefinition to override a more generat one.

Traditionally, access control has been studied in the areas of operating systems and database management systems. With the advent of multiuser interfaces, there is a need to provide access control in the user interface. We have developed a general framework for supporting access control in multiuser interfaces. It is based on the classical notion of an access matrix, a generalized editing-based model of user-application interaction, and a flexible model of user-user coupling. It has been designed to support flexible control of all significant shared operations, high-level specification of access control policies, and automatic and efficient implementation of access control in a multiuser interface. It supports several new kinds of protected objects including sessions, windows, and hierarchical active variables; a large set of rights including not only the traditional semantic rights but also interaction and coupling rights; a set of inference rules for deriving default permissions; and a programming interface for implementing access control in multiuser interfaces. We have implemented the framework as part of a system called Suite. This article describes and motivates the framework using the concrete example of Suite, identifies some of the difficult issues we faced in its design, describes our preliminary experience with it, and suggests directions for future work.

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