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 multi-user tools makes the existence of jointlyowned objects a necessity: a participant who joins a multi-uscr tool written by others knows that the user agent executed in his name is not a Trojan horse if the multi-user tool is jointly owned by all the participants. In this paper, 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. Authorityand quorum-based objects are investigated as instances of conditionally joinly-owncd objects. We show that conditionally jointlyowned objects can also be used to resolve the 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 demonsuate the usefulness of conditionally jointly-owned objects.