Basic BDI Agent

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Basic BDI Agent

• Dan Rochowiak
• drochowi_at_cs.uah.edu

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The basics
Desired Agent Properties Autonomy Proactive Reac
tive Social
Agent
Sensor Input
Action Output
Environment
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Intuitions

• Beliefs (Bel) represent the information the agent
  has about the world.
• Desires represent states of affairs (soa) that
  the agent wants to be true
• Intentions (Int) represent deires that the agent
  has committed to achieving.

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Formalism example

• (Int i soa) gt (Bel i soa)
• If the agent (i) intends the state of affairs
  (soa), then it is not the case that the agent (i)
  believes that the state of affairs (soa) obtains.

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Practical reasoning

• Theoretical reasoning is about belief.
• In theoretical reasoning the concern is for the
  transfer of truth or its surrogate
• Practical reasoning is about action not belief.
• In practical reasoning the concern is for the
  production of an action

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Practical reasoning

• Practical reasoning involves deliberation and
  planning (means-ends)
• Deliberation focuses on deciding what soa we want
  to achieve
• Means-ends reasoning (planning) focuses on
  deciding how to achieve the specified soa.
• All practical reasoning understood as computation
  is resource bound

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Intentions

• Intentions lead to action and drive means-end
  reasoning (pro-active).
• Intentions endure over time (persistence)
• Intentions constrain future deliberation.
• Intentions refer to future soa.

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Two cases

• Having the intention to bring about soa while
  believing that you will not bring about soa is
  called intention-belief inconsistency and is held
  to be irrational
• Having the intention to bring about soa while not
  believing that soa will be the case is called
  intention-belief incompleteness and is rational

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The other cases

• Having the intention to bring about soa while
  believing that soa is the case is
• Having the intention to bring about soa while not
  believing that soa is the case is
• Having the intention to bring about soa while
  believing that soa will be the case is

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Basic agent control

• While true
• Observe environment
• Update internal world model
• Deliberate about intention
• Get plan for intention
• Execute plan
• End while

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Plans

• Preconditions define the circumstances under
  which the plan is applicable
• Postconditions define the soa the plan achieves
• Body is the sequence of actions
• Let pl be a plan and Plans be the set of all plans

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Plans

• If pl is a plan, then pre(pl), post(pl) and
  body(pl) are the precondition, the postcondition
  and the body of the plan.
• If pl is a plan, then empty(pl) is an empty
  sequence.
• If pl is a plan, then execute(pl) is a procedure
  that executes the plan without stopping

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Plans

• If pl is a plan, then head(pl) is the plan with
  the first action of body(pl)
• If pl is a plan, then tail(pl) is the plan with
  all but the first action of body(pl)
• If pl is in Plans, i is in Int and b is in Bel,
  then sound(pl,i, b) means that pl is a sound plan
  for achieving i.

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As the world changes

• The function brf(b,p) is the belief revision
  function that changes Beliefs given a new percept
  p.
• The function deliberate(b) returns an intention
  from Beliefs
• The function plan(b,i) returns a plan from the
  current Beliefs and Intentions

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New control

• Let B be Beliefs
• While true
• Get next p (percept)
• Let B be brf(B,p)
• Let I be deliberate(B)
• Let pl be plan(B,I)
• execute(pl)
• End while

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Deliberation

• Deliberation has two parts
• Generate a set of possible alternatives
• The function options(B,I) takes Beliefs and
  Intentions and generates Desires
• Select between competing alternatives and commit
  to achievement
• The function filter(B,D,I) takes Beliefs,
  Desires, and Intentions and returns a new
  Intentions

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Revised control

• Let B be Beliefs
• Let I be Intentions
• While true
• Get next p
• Let B be brf(B,p)
• Let D be options(B,I)
• Let I be filter(B,I)
• Let pl be plan(B,I)
• execute(pl)
• End while

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Commitment

• Once there is commitment one might blindly trudge
  ahead or
• Revise plans when a plan fails or
• Drop impossible or successful intentions

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The final general version

• Let B be Beliefs
• Let I be Intentions
• While true

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The final general version

• Get next p
• Let B be brf(B,p)
• Let D be options(B,I)
• Let I be filter(B,D,I)
• Let pl be plan(B,I)

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The final general version

• While not (empty(pl) or succeeded(I,B) or
  impossible(I,B))
• Let A be head(pl)
• execute(A)
• Let pl be tail(pl)

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The final general version

• Get next p
• Let B be brf(B,p)
• If not sound(pl,I,B) then
• Let pl be plan(B,I)
• End if
• End while
• End while