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The BDI model

In general, an architecture built on the BDI model of agency is specified in terms of the following data structures:

bdi.jpg

Beliefs. They represent information about the world. Each belief is represented as a ground literal of first-order logic. Two activities of the agent update its beliefs:

  1. The perception of the environment.
  2. The execution of intentions.

Desires. Also known as goals, they correspond to the tasks allocated to the agent and are usually considered as logically consistent among them. Two kinds of desires are usually adopted:

  1. To achieve a desire, expressed as a belief formula, that is, a literal not necessarily grounded.
  2. To test a situation expressed as a situation formulae, that is a belief formula or a disjunction and/or a conjunction of them.

Event queue. Perceptions of the agent are mapped to events stored in a queue. Events are of three kinds:

  1. The acquisition or removal of a belief.
  2. The reception of a message.
  3. The acquisition of a new goal.

Plans. BDI agents usually have a library of predefined plans. Each plan has several components. The plan-id is used to identify a plan in the plan library. The plan body represents possible courses of action. It is a tree which nodes are considered as states and arcs are actions or goals of the agent. External actions are like procedures the agent can execute directly. Goals are posted to the event queue when the plan is executed, then other plans that can deal with such events are considered, and so on. Additionally, a plan have some maintenance conditions which describes the circumstances that must remain to continue the execution of the plan. A set of internal actions is specified for the cases of success and failure of the plan. Finally, some BDI architectures include some measure of the utility of the plan.

Intentions. They are courses of action an agent has commited to carry out. Each intention is implemented as a stack of plan instances. Two cases are possible:

  1. If the event is an external one, which means no plan has generated it, then an empty stack is created and the plan instance selected is pushed on it
  2. If the event is an internal one, it means that a previous plan generated it, then the plan instance is pushed on the existing stack containing this previous plan

Overall control/data flow of BDI architecture is as follows

bdi.gif

-- AndreySalnikov? - 27 May 2004


Attachment sort Action Size Date Who Comment
bdi.jpg manage 82.5 K 31 May 2004 - 20:03 AndreySalnikov?  
bdi.gif manage 5.1 K 01 Jun 2004 - 06:41 AndreySalnikov?  

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Topic revision r1.4 - 01 Jun 2004 - 08:05 GMT - AndreyUstyuzhanin
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