Epistemic planning for single- and multi-agent systems

Abstract

ABSTRACT. In this paper, we investigate the use of event models for automated planning. Event models are the action defining structures used to define a semantics for dynamic epistemic logic. Using event models, two issues in planning can be addressed: Partial observability of the environment and knowledge. In planning, partial observability gives rise to an uncertainty about the world. For single-agent domains, this uncertainty can come from incomplete knowledge of the starting situation and from the nondeterminism of actions. In multi-agent domains, an additional uncertainty arises from the fact that other agents can act in the world, causing changes that are not instigated by the agent itself. For an agent to successfully construct and execute plans in an uncertain environment, the most widely used formalism in the literature on automated planning is "belief states": sets of different alternatives for the current state of the world. Epistemic logic is a significantly more expressive and theoretically better founded method for representing knowledge and ignorance about the world. Further, epistemic logic allows for planning according to the knowledge (and iterated knowledge) of other agents, allowing the specification of a more complex class of planning domains, than those simply concerned with simple facts about the world. We show how to model multi-agent planning problems using Kripke-models for representing world states, and event models for representing actions. Our mechanism makes use of slight modifications to these concepts, in order to model the internal view of agents, rather than that of an external observer. We define a type of planning domain called epistemic planning domains, a generalisation of classical planning domains, and show how epistemic planning can successfully deal with partial observability, nondeterminism, knowledge and multiple agents. Finally, we show epistemic planning to be decidable in the single-agent case, but only semi-decidable in the multi-agent case.

BDI Logics for BDI Architectures: Old Problems, New Perspectives

“…Consequently, the planning community recently moved towards multiagent planning problems [37]. This is paralleled by an interest in planning in the DEL community [5].…”

“…A path p associates to every non-negative integer t a set of propositional symbols and an action: the propositional symbols that are true at t and the action that is going to be performed by the agent at t. A set of paths P is appropriate if (1) on each path, the postcondition of each action at time tþ1 is true and (2) once the precondition of each action is satisfied at time t on p then it must be performed on some path that is identical to p up to time tÀ1. 5 Intuitively, B and I are coherent if the agent considers it possible to do all actions she intends with respect to some appropriate set of paths. Based on this formalization, Icard et al propose AGM-like postulates for the joint revision of beliefs and intentions and provide a representation theorem.…”

Learning Actions Models: Qualitative Approach

“…Some of the notions defined above are known from existing literature [7,8,16]. The newly introduced notions are precondition-free, universally applicable, and normal actions, as well as actions with basic preconditions.…”

“…We here use a variant that includes postconditions [8,7], which means that actions can have both epistemic effects (changing the beliefs of agents) and ontic effects (changing the factual states of affairs).…”

“…A language, interpreted on epistemic models, allows expressing conditions under which an action takes effect (so-called preconditions), and the effects of such actions (so-called postconditions). This setting is particularly useful for modeling the process of epistemic planning (see [7,1]): one can ask which sequence of actions should be executed in order for a given epistemic formula to hold in the epistemic model after the actions are executed.…”