Actions with Typical Effects: Epistemic Characterization of Scenarios.
Barbara Dunin‐Kȩplicz, Anna Maria Radzikowska · 1995
To meet recent requirements regarding modelling the behaviour of a rational agent in a multi-agent system one has to cope with the complexity of actions with typical, but not necessarily certain results. The generic characteristics of these actions, called ~,-actions, is that they have different effects in typical and atypical performances. We model these actions by extending the epistemic/dynamic framework presented in [1] designed to deal with both knowledge and abilities of agents, and with effects of actions they perform. A general notion of agent’s abilities covers physical, mental and moral capacities and is formalized by an expression Aia which states that agent i is capable to perform the action a. Epistemic aspect of agent is expressed in terms of the formula K~ which states that the agent i knows the fact represented by ~. We consider actions of two kinds: traditionally viewed basic actions with certain effects (atomic actions, sequential composition, conditional action or repetitive action) and atomic ~-actions. The results of basic actions performed by an agent are formalized by the the following formula from (propositional) dynamic logic ~, denoting the fact that the agent i has the opportenity to perform action a and that doing leads to ~. Simillary, the result of performing ~action is represented by ~o, ¢, denoting that the agent i has the opportunity to perform the action a and as a result of this event ~ (always) holds and t~/pically ~ holds. Both kinds of actions are assumed to be deterministic. By SCD(i, (Tpr,} {Tp..,}) we denote a scenar/o which is viewed as a sequence of basic and/or atomic A-actions to be performed by an agent i, together with initial (Tpre) and final (Tpo,,) observations. Rational agents usually deal with scenarios rellecting a ~typical pattern of behaviour, i.e. s/he prefers to perform typically as many actions as possible. This scenario realization is formalized in terms of a nonmonotonic preferential strategy which amounts to minimization of atypical performances of actions.