Jointly-owned objects for collaboration: Operating-system support and protection model

As real-time collaboration becomes more frequent, it is common for a group of users to create and own an object jointly. The use of multiuser tools makes the existence of jointly-owned objects a necessity: a participant who joins a multiuser tool written by others knows that the user agent executed in his name will not allow unauthorized access to other objects if the multiuser tool is jointly owned by all participants. In this article, we discuss the requirements and issues behind jointly-owned objects. By generalizing these requirements, we have implemented a conditionally jointly-owned object. The conditions take the form of a quorum or a list of users who have the rights to access an object or to change its protection state. We sketch a design of conditionally jointly-owned objects, and apply the same concepts to subjects. Authority- and quorum-based objects are investigated as examples of conditionally jointly-owned objects. We show that conditionally jointly-owned objects can also be used to resolve conflicts that may arise among joint owners. We generalize Graham and Denning's protection model to incorporate these jointly-owned entities. Operating-system support for conditionally jointly-owned objects is specified at the system-call level. Examples are provided to demonstrate the usefulness of conditionally jointly-owned objects.