Introduction

Intelligent agents are software entities that carry out a set of operations on behalf of a user or another program. They operate with a certain degree of autonomy, employing some knowledge of the user's goals. Multi-agent systems are complex systems comprised of multiple intelligent agents that act either independently or in cooperation with one another.

According to Jennings et al. [1998], multi-agent systems share a number of key characteristics: (a) each agent has incomplete information or capabilities for solving the problem and, thus has a limited viewpoint; (b) there is no system global control; (c) data is decentralised; and (d) computation is asynchronous. The aforementioned characteristics make multi-agent systems a suitable method for modelling, simulation and analysis of real-life complex systems. In recent years, many researchers have contributed valuable work in multi-agent systems, which is applicable to many disciplines including economics [Kaihara, 2001], sociology [Rodrigues et al., 2003], organisation and management science [Huin, 2004] and biology [Guo et al., 2005].