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The formal definition of an autonomous software agent

The word agent use usually in one or both of two common uses: 1) one who acts, or who can act, and 2) one who acts in place of another with permission. Since "one who acts in place of " acts, the second usage requires the first. It is necessary to go from definition of the first notion.

This definition assumes the following characteristic properties of the agents. Each is situated in, and is a part on some environment. Each senses its environment and act autonomously upon it. No other entity is required to feed it input, or to interpret and use its output. Each acts in pursuit of it's own agenda, whether satisfying evolved drives as in humans and animals, or pursuing goals designed in by some other agent, as in software agents. (Artificial life agents may be of either variety.) Each acts so that its current actions may effect its later sensing, that is its actions effect its environment. Finally, each acts continually over some period of time. A software agent, once invoked, typically runs until it decides not to. An artificial life agent often runs until it's eaten or otherwise dies. Of course, some human can pull the plug, but not always. Mobile agents on the Internet may be beyond calling back by the user. Let's formalize them into a definition.

An autonomous agent is a system situated within and a part of an environment that senses that environment and acts on it, over time, in pursuit of its own agenda and so as to effect what it senses in the future.

It is important, that the Independent agents are located in some environment. Change the environment and we may no longer have an agent. A robot with only visual sensors in an environment without light is not an agent. And, second, the software agents defined by their tasks. Tasks can be specified so as to require agents to fulfill them.

What about ordinary programs? All software agents are programs, but not all programs are agents.

Subroutines of agents need not be agents for the same reasons that programs need not be. However agents can have subagents.

Such definition of an autonomous agents has succeeded in distinguishing between agents and programs. Software agents are, by definition, programs, but a program must measure up to several marks to be an agent. The class of the agents, which is allocated with such definition, is very great. So, practically the subclasses of the named class determined by the various purposes of creation of the agents will be useful.

Agent Classifications

Agents may be usefully classified according to the subset of following properties that they enjoy.

Property Other Names Meaning

reactive (sensing and acting) responds in a timely fashion to changes in the environment

autonomous exercises control over its own actions

goal-oriented pro-active purposeful does not simply act in response to the environment


continuous is a continuously running process

communicative socially able communicates with other agents, perhaps including people

learning adaptive changes its behavior based on its previous experience

mobile able to transport itself from one machine to another

flexible actions are not scripted

character believable "personality" and emotional state
Every agent satisfies the first four properties. Adding other properties produces potentially useful classes of agents, for example, mobile, learning agents. Thus a hierarchical classification based on set inclusion occurs naturally. Mobile, learning agents are then a subclass of mobile agents.

Multi-agent systems

Agents can have subagents. For example, the file system maintenance agent, can be thought of as a single agent, or as a multi-agent system consisting of Wanderer, Compressor, Back-Up and Sleepy. Each of these have independent access to sensors (certain unix commands such as ls) and to actions (other unix commands such as cd), and each has its own simple agenda. Also, each runs continuously, and acts so as to effect its next sensing. Thus, each may be considered an agent in it's own right, and hence a subagent. As a multi-agent system, such agent is particularly simple in that there is almost no communication between the subagents. Each is, of course, privy to sensing initiated by the others, and Sleepy's action effects the others. Also, each subagent sometimes suppresses the actions of the lower layers. One might ask if Wanderer is truly autonomous if Compressor can suppress its actions. A person in jail, or in an elevator, has lost some freedom of movement, but is still autonomous. Environment may be expected to imposes limits on an agent's actions.

It is possible to name a system with no communication between its subagents a discrete multi-agent system. A multi-agent system in which each agent communicates with every other might be called fully connected,. Thus multi-agents systems can be classified according to the possible communications paths through the system. It is possible also classify such systems by their communications bandwidth.

In addition to multi-agent systems that can reasonably be viewed as constituting a single agent, other multi-agent system are better classified as societies of agents. For example, when a collection of scheduling agents gather to schedule a meeting between their users, they pursue a common goal and intelligent group behavior emerges. Yet, as a group, definition of agent is not met in that persistence is missing. When scheduling is complete, agents disperse, perhaps never to gather again in this same grouping. One could argue that the collection of all such scheduling agents at a given site constitute a single agent. To do so, the notions of sensing, acting, and having its own agenda would have to be considerably stretched.

An attempt has been made to capture the essence of agency in a formal definition, which allows a clear distinction between a software agent and an arbitrary program. The beginnings of a natural kinds taxonomy for autonomous agents is proposed, as is further classification via collections of features.

The formal definition fixing essence of the independent program agent is offered which allows a clear distinction between a software agent and an arbitrary program , and approach to classification of the agents allows on the basis of the allocated set of properties.

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