Dealing with Space in Multi–Agent Systems: a model for Situated MAS Stefania Bandini, Sara Manzoni, Carla Simone Department of Computer Science, Systems and Communication University of Milano - Bicocca, Italy {bandini,manzoni,simone}@disco.unimib.it ABSTRACT The paper introduces the Multilayered Multi–Agent Situ- ated System (MMASS). The MMASS allows tha descrip- tion of situated agents that is, agents sensitive to the spa- tial relationships that determine constraints and abilities for actions as well as privileged cooperation relationships. The main feature of the MMASS model is to give an explicit def- inition of the spatial structure of the environment in which the system of situated agents acts and interacts. Agent en- vironment, possibly multilayered, can reproduce a physical space. It is nevertheless possible to define a ‘virtual space’ that agents can roam and where they interact. Interactions take place when two or more agents are brought into dy- namic spatial relationship through a set of reciprocal ac- tions, and have an influence on the future behavior of the agents. There are several application domains that require the representation of the space in order to take advantage in the multi–agent approach. Typical examples of these do- mains are the Multi–Agent Based Simulation (MABS) and the Computer Supported Cooperative Work (CSCW). Two specific problems of these domains will be used in the paper to illustrate the MMASS model. Categories and Subject Descriptors I.2.11 [Artificial Intelligence]: Distributed Artificial In- telligence—Multi Agent Systems, Languages and Structure ; I.6.5 [Simulation and Modelling]: Model Development General Terms Languages 1. INTRODUCTION The main aim of this work is to present the Multilayered Multi–Agent Situated Systems (MMASS) model. A situated agent lives in an environment where the space is explicitly Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for pro£t or commercial advantage and that copies bear this notice and the full citation on the £rst page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior speci£c permission and/or a fee. AAMAS’02, July 15-19, 2002, Bologna, Italy. Copyright 2002 ACM 1-58113-480-0/02/0007 ...$5.00. structured. In [11] the concept of situated agent is intro- duced, without any explicit reference to the spatial structure of the environment. At our knowledge no other proposal in the literature dealing with interaction between agents and their environment or modelling the environment takes into account its spatial structure. We claim that there are several application domains that require an explicit representation of the spatial structure of the environment in order to take advantage of a multi–agent approach. The MMASS model describes the spatial structure of the environment as a multilayered network of sites. Moreover, it defines a set of influences generated by agents and prop- agating along the edges of the network and leaving on sites information about their presence. Agents situated in this en- vironment are strongly influenced by their position that is, the site of the space in which they are situated. This kind of Multi–Agent System (MAS) is based on a perception– deliberation–action mechanism, that describes agents as char- acterized by a set of possible actions, and on a mechanism for the selection of the action to be undertaken based on the internal state and the position of the agents themselves. In particular, the position in the environment defines the situ- ation in which agents are acting, where “situation” refers to a potentially complex combination of internal and external events and states [6]. Situated MAS are generally made of reactive agents that is, elementary memoryless agents with a defined position in time and space. Reactive situated agents perform their actions as a consequence of the perception of signals coming either from other agents or from the envi- ronment, and are sensitive to the spatial relationships that determine constraints and abilities for actions as well as priv- ileged cooperation relationships. The environment where agents are situated can reproduce a physical space. It is nevertheless possible to define a “virtual space” that agents can roam and where they interact. Interactions take place when two or more agents are brought into dynamic spatial relationship through a set of reciprocal actions, and have an influence on the future behavior of the agents. A formalized description of the basic principles of the MMASS model together with examples of its application are reported in this paper. This work is part of a larger project whose aim is to develop a tool to support the de- sign, development and execution of applications according to the MMASS approach. The work presented here gives the basis to provide designers with a language and a framework for the development of systems of agents that are charac- terized and influenced by their spatial position and where