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What are Agent?
An agent is anything that can perceive its environment through sensors and acts upon that environment through effectors.
- A human agent has sensory organs such as eyes, ears, nose, tongue and skin parallel to the sensors, and other organs such as hands, legs, mouth, for effectors.
- A robotic agent replaces cameras and infrared range finders for the sensors, and various motors and actuators for effectors.
- A software agent has encoded bit strings as its programs and actions.
The Types of Intelligent Agents
Agent’s structure can be viewed as −
- Agent = Architecture + Agent Program
- Architecture = the machinery that an agent executes on.
- Agent Program = an implementation of an agent function.
1. Simple Reflex Agents
- They choose actions only based on the current percept.
- They are rational only if a correct decision is made only on the basis of current precept.
- Their environment is completely observable.
Condition-Action Rule − It is a rule that maps a state (condition) to an action.
2. Model Based Reflex Agents
They use a model of the world to choose their actions. They maintain an internal state.
Model − The knowledge about “how the things happen in the world”.
Internal State − It is a representation of unobserved aspects of current state depending on percept history.
Updating the state requires the information about −
- How the world evolves.
- How the agent’s actions affect the world.
3. Goal Based Agents
They choose their actions in order to achieve goals. Goal-based approach is more flexible than reflex agent since the knowledge supporting a decision is explicitly modeled, thereby allowing for modifications.
Goal − It is the description of desirable situations.
4. Utility Based Agents
They choose actions based on a preference (utility) for each state. Goals are inadequate when −
- There are conflicting goals, out of which only few can be achieved.
- Goals have some uncertainty of being achieved and you need to weigh likelihood of success against the importance of a goal.
Non-monotonic Reasoning
The definite clause logic is monotonic in the sense that anything that could be concluded before a clause is added can still be concluded after it is added; adding knowledge does not reduce the set of propositions that can be derived.
A logic is non-monotonic if some conclusions can be invalidated by adding more knowledge. The logic of definite clauses with negation as failure is non-monotonic. Non-monotonic reasoning is useful for representing defaults. A default is a rule that can be used unless it overridden by an exception.
For example, to say that b is normally true if c is true, a knowledge base designer can write a rule of the form
b ←c ∧ ∼ aba.
where aba is an atom that means abnormal with respect to some aspect a. Given c, the agent can infer bunless it is told aba. Adding aba to the knowledge base can prevent the conclusion of b. Rules that imply abacan be used to prevent the default under the conditions of the body of the rule.
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