As computer Systems become ubiquitous and more information becomes available electronically, it is increasingly important for computer systems to be able to collaborate with each other and their users. The develop ment of the underlying theories and formalization needed to build collaborative systems will have far- reaching practical import as well as addressing challenging computer science problems. The Shared Plan formalization of collaboration (Grosz and Kraus, 1995; Grosz and Kraus, 1993) provides a specification of the capabilities to act and mental attitudes that agents must have to participate in collaborative activities with one another. This formalization will be extended developing strategies for elabmrating partial plans by specifying axioms that treat more completely the attitude of intending that a proposition hold. In addition a collaborative communication system based on Shared Plans will be designed: this system will both demonstrate the value of a model of collaboration to the design of human-computer interface systems and test the formalization. The proposed research will contribute to the development of computer agents that are fully collaborative, with each other and their users; it will also enable the construction of more flexible and user-friendly interfaces.
