Chapter 2
We will use the concept of a rational agent to define a system that can be called intelligent. Well define rational agents that behaves as well as possible in a given environment.
2.1 agents and environments
An agent is anything that can be viewed as perceiving its environment through sensors and acting upon that environment through actuators.
Percept the agents perceptual inputs at any given instant. Percept sequence complete history of everything the agent has ever perceived. An agents choice at any time can depend on the entire percept sequence observed to date.
Mathematically speaking, we say the agents behavior is defined by the agent function that maps any given percept sequence to an action.
Tabulating the agent function would result in a giant unusable table and take up too much space to be stored. The table might be an external characterization, and the agent function is an internal thing implemented by an agent program.
The notion of an agent is a tool for analyzing systems, not an absolute characterization that divides the world into agents and non-agents
2.2 good behavior: the concept of rationality
A rational agent does the right thing: that which will make the agent the most successful. Thus we need to quantify success.
Performance measures
A performance measure embodies the criterion for success of an agents behavior
An agent generates a sequence of actions in response to percepts. The sequence causes state transitions. If the sequence is desirable, the agent performed well. Agents should not have subjective opinions about their success or they would report it all the time, thus we must have objective performance measurements imposed by the agents designer(s).
As a general rule, it is better to design performance measures according to what you want in the environment, rather than according to how one thinks the agent should behave.
Averages of behavior are confusing, as there could be dramatic highs or lows whose average is equivalent to that of a stable system that has no major fluctuations.
Rationality
Rationality depends on four things
o Performance measures used as criterion of success
o Agents prior knowledge of the environment
o Actions the agent can perform
o Agents percept sequence to date
The definition of a rational agent is that for each possible percept sequence, a rational agent should select an action it expects to maximize its performance measure, given the evidence provided by the percept sequence and whatever built-in knowledge the agent has.
We need to define a performance measure in terms of the environment, inputs and outputs (percepts and actuators).
Omniscience, learning and autonomy
Difference between rationality and omniscience: an omniscient agent knows the actual outcome of its actions but this isnt possible in reality. Rationality is not the same as perfection. Rationality maximizes expected performance, while perfection maximizes actual performance.
Our definition of rationality doesnt require omniscience. Rational choices depend on percept sequence to date. We must ensure we dont allow the agent to behave decidedly underintelligently. (example of crossing the street, if a piano was dropped on a rational agent trying to cross a street we couldnt call it irrational thats an odd circumstance)
Rational agents must be able to gather information and learn as much as possible from what it perceives.