24.12, An Introduction to Multiagent Systems

Notes taken from 'An Introduction to Multiagent Systems' (2002), by Michael Wooldridge

12, Logics for Multiagent Systems

(Why Modal Logic?, Possible-Worlds Semantics for Modal Logics)

Normal Modal Logics

The basic possible-worlds approach has the following disadvantages as a multiagent epistemic logic:

- agents believe all valid formulae;
- agents' beliefs are closed under logical consequence;
- equivalent propositions are identical beliefs; and
- if agents are inconsistent, then they believe everything.

Epistemic Logic for Multiagent Systems

Pro-attitudes: Goals and Desires

An obvious approach to developing a logic of goals or desires is to adapt possible-worlds semantics. In this view, each goal-accessible world represents one way the world might be if the agent's goals were realised. However, this approach falls prey to the side effect problem, in that it predicts that agents have a goal of the logical consequences of their goals (cf. the logical omniscience problem). This is not a desirable property: one might have a goal of going to the dentist, with the necessary consequence of suffering pain, without having a goal of suffering pain.

Common and Distributed knowledge

Integrated Theories of Agency

When building intelligent agents - particularly agents that must interact with humans - it is important that a rational balance is achieved between the beliefs, goals, and intentions of agents.

"For example, the following are desirable properties of intention: an autonomous agent should act on its intentions, not in spite of them; adopt intentions it believes are feasible and forego those believed to be infeasible; keep (or commit to) intentions, but not forever; discharge those intentions believed to have been satisfied; alter inentions when relevant beliefs change; and adopt subsidiary intentions during plan formation." (Cohen and Levesque, 1990)

Recall the properties of intentions, as discussed in Chapter 4.

(1) Intentions pose problems for agents, who need to determine ways of achieving them.
(2) Intentions provide a 'filter' for adopting other intentions, which must not conflict.
(3) Agents track the success of their intentions, and are inclined to try again if their attempts fail.
(4) Agents believe their intentions are possible.
(5) Agents do not believe they will not bring about their intentions.
(6) Under certain circumstances, agents believe they will bring about their intentions.
(7) Agents need not intend all the expected side effects of their intentions.

Formal Methods in Agent-Oriented Software Engineering