What is an agent?

Michael Wooldridge (1994)

Carl Hewitt recently remarked that the question what is an agent? is embarrassing for the agent-based computing community in just the same way that the question what is intelligence? is embarrassing for the mainstream AI community. The problem is that although the term is widely used, by many people working in closely related areas, it defies attempts to produce a single universally accepted definition. This need not necessarily be a problem: after all, if many people are successfully developing interesting and useful applications, then it hardly matters that they do not agree on potentially trivial terminological details. However, there is also the danger that unless the issue is discussed, ‘agent’ might become a ‘noise’ term, subject to both abuse and misuse, to the potential confusion of the research community.

Michael Wooldridge (1994)

Perhaps the most general way in which the term agent is used is to denote a hardware or (more usually) software-based computer system that enjoys the following properties:

• autonomy: agents operate without the direct intervention of humans or others, and have some kind of control over their actions and internal state;
• social ability: agents interact with other agents (and possibly humans) via some kind of agent-communication language (Genesereth and Ketchpel, 1994);
• reactivity: agents perceive their environment, (which may be the physical world, a user via a graphical user interface, a collection of other agents, the INTERNET, or perhaps all of these combined), and respond in a timely fashion to changes that occur in it;
• pro-activeness: agents do not simply act in response to their environment, they are able to exhibit goal-directed behaviour by taking the initiative.