I was cribbing to a colleague of mine that I had to give an example of a specific kind of multiagent system, a kind that I think didn't exist. The colleague suggested that it would be impossible to do that because there is not a single multiagent system in the world, let alone a specific kind.
He couldn't be more wrong. Multiagent systems are everywhere; it is just that we build these systems without using agent-oriented concepts, so we do not see them as such. The application eBay is a multiagent system: it involves eBay (the organization), bidders, sellers, payment processors, and so on. The application Orbitz is a multiagent system: it involve customers, airlines, Orbitz (the organization), credit card companies, banks, and so on. Your home security system is a multiagent system if it includes active monitoring by a security agency. These are multiagent systems because they involve interactions between autonomous parties, in other words agents.
You and your microwave do not constitute a multiagent system: the microwave is under your control. However, it would be a multiagent system if your microwave could say "No, I don't want to defrost the chicken now". Whereas you and the security agency that installed the sensors constitute a multiagent system, neither two or more sensors by themselves nor the sensors in conjunction with you constitute one. There is no sense in which such a sensor is autonomous in relation to you nor in relation with other sensors.
Every agent is a component, but not every component is an agent. Every multiagent system is necessarily distributed, but not every distributed system is a multiagent system.
The only test of agenthood is autonomy. Something is not an agent because it has a sense, reason, act (SRA) loop. Autonomy can only be understood in relation with other agents; the SRA loop is about the internal construction of the agent. Whether a bidder on eBay is a human or "intelligent" software using an SRA loop or "stupid" software -- for example, one that blindly raises its bid every so often -- does not change the fact that they are all agents.
An agent is not an agent because it is written in JADE or WADE (agent-oriented programming languages); it is not one because it was modeled and designed using agent-oriented abstractions. Anything that is autonomous is an agent; anything that is not is not an agent, and labeling such a thing as an agent is to abuse the term. In fact, the term "autonomous agent" is redundant in itself.
As multiagent system researchers, our goal is to enable their programming in a way that accommodates autonomy.
