User Modeling and User-Adapted Interaction 9: 45–78, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 45 Mixed-Initiative Issues in an Agent-Based Meeting Scheduler AMEDEO CESTA 1 and DANIELA D’ALOISI 2 1 IP-CNR, Consiglio Nazionale delle Ricerche, Viale Marx 15, I-00137 Rome (Italy) e-mail: amedeo@pscs2.irmkant.rm.cnr.it 2 FUB, Fondazione Ugo Bordoni, Via B. Castiglione 59, I-00142 Rome (Italy) e-mail: dany@fub.it (Received: 16 November 1997; accepted in revised form: 13 May 1998) Abstract. This paper concerns mixed-initiative interaction between users and agents. After clas- sifying agents according to their task and their interactivity with the user, the critical aspects of delegation-based interaction are outlined. Then MASMA, an agent system for distributed meeting scheduling, is described, and the solutions developed to control interaction are explained in detail. The issues addressed concern: the agent capability of adapting its behavior to the user it is supporting; the solution adopted to control the shift of initiative between personal agents, their users and other agents in the environment; the availability of features, e.g. the inspection mechanism, that endow the user with a further level of control to enhance his sense of trust in the agent. Key words: personal assistants, mixed-initiative interaction, multi-agent systems, human computer interaction. 1. Introduction The term mixed-initiative usually refers to dialogue systems (Walker & Whittaker, 1990), in which the turns of conversation, along with an analysis of the type of utterances, determine which actor has control of the dialogue. There are several possible definitions for the term and different contexts in which mixed-initiative models can be applied (see for example (Allen et al., 1996; Lochbaum et al., 1990; Lester et al., 1998; Hagen, 1998)). An overview is presented in (Cohen et al., 1998) that shows several case studies where the actors can be either two people or a person and a system. It is interesting to understand how the definition for mixed-initiative changes when the system is an intelligent autonomous agent. In this paper, mixed-initiative issues are considered in the scenario offered by a specific personal assistant, a meeting scheduler. This context seems particularly suitable to verify the usefulness of an agent-based assistant, although an under- evaluation of issues concerning the user-agent interaction might prevent the user from actually using the system. A possible solution was to consider the agent- user pair as a mixed-initiative system and to test how mixed-initiative models were able to describe the flow of the interaction between the two. The system, named 195830.tex; 2/08/1995; 8:40; p.1 INTERPRINT: J.N.B. user167 (userkap:mathfam) v.1.15