This paper proposes a generic approach to planning in the presence of incomplete information. The approach builds on an abstract notion of a belief state representation, along with an associated set of basic operations. These operations facilitate the development of a sound and complete transition function, for reasoning about effects of actions in the presence of incomplete information, and a set of abstract algorithms for planning. The paper demonstrates how the abstract definitions and algorithms can be instantiated in three concrete representations: minimal-DNF, minimal-CNF, and prime implicates, resulting in three highly competitive conformant planners: DNF, CNF, and PIP. The paper includes an experimental evaluation of the planners DNF, CNF, and PIP and proposes a new set of conformant planning benchmarks that are challenging for state-of-the-art conformant planners.
Motivation and Related WorkPlanning in the presence of incomplete information [Goldman and Boddy 1996;Smith and Weld, 1998] is the problem of generating a plan that can achieve a given goal regardless of what the actual truth value of unknown information about the initial world is. This paper focuses on conformant planning-a special class of planning problems in the presence of incomplete informationthat deals with incomplete information about the initial state and with deterministic and non-sensing actions.One of the challenges in conformant planning is the problem of reasoning about action effects in the presence of incomplete information. Specifically, consider an action a with a set of conditional effects of the form (a : ψ → η), where ψ and η are a set of literals. Each * This paper is based on the journal article [To, Son, and Pontelli, 2015]. effect (a : ψ → η) denotes that the set of literals η will be true in the resulting state after the execution of a in the current state if the e-condition ψ is true in the current state. Due to incomplete information, the current state and, hence, the truth value of ψ in it can be unknown. As a consequence, the fact that η must be true in the successor state can be unknown, making the computation of the successor state particularly challenging. This agrees with the results in [Baral et al., 2000;Haslum and Jonsson, 1999], that conformant planning for domains with conditional effects is at a higher complexity level than that without conditional effects. Since its introduction, conformant planning has attracted the attention of several researchers-leading to the development of several state-of-the-art conformant planners. It is important to observe that most efficient conformant planners are best-first search and progression-based planners, whose development starts with the selection of a representation language for incomplete (partially known) states and the definition of a transition (progression) function that, given a state S and an action, computes the next state S of the world, where S and S are generally incomplete and encoded in the representation.To deal with incomplete information a...