IPC-4 Probabilistic Planning Track : FAQ 1 . 0 September 2003
The 2004 International Planning Competition, IPC-4, will include a probabilistic planning track for the first time. This document provides some of the high level decisions that have been made concerning how the competition will be run. The 2004 International Planning Competition, IPC-4, will include a probabilistic planning track for the first time. This document lays out some of the high level decisions that have been made concerning how the competition will be run. The details are still in flux at the time of this writing, and we hope to get feedback from the participants to spelled them out more precisely during the fall. The overriding goal of the probabilistic planning track is to bring together two communities converging on a similar set of research issues and aid them in creating comparable tools and approaches. One community consists of Markov decision process (MDP) researchers interested in developing algorithms that apply to powerfully expressive representations of environments. The other consists of planning researchers incorporating probabilistic and decision theoretic concepts into their planning algorithms. Cross fertilization has begun, but the probabilistic planning track promises a set of shared benchmarks and evaluation metrics that could crystallize efforts in this domain of study. This document represents a snapshot of the ongoing development of the IPC-4 probabilistic track. For the latest developments, please visit: http://www.cs.rutgers.edu/∼mlittman/topics/ ipc04-pt.html. Frequently Asked Questions There are many issues to be ironed out as part of establishing the new track, but there are some issues that are mostly decided at this point. Here are some clarifying questions and their answers. What domain description language will be used to represent probabilistic domains? That’s a great first question. We are creating a new domain description language, sketched in the second section of this document. It is modeled on PDDL 2.1, the domain description language for deterministic domains that has been used in the IPC in the past. Syntactically, this language has a STRIPS-like flavor, but includes probabilistic constructs. By basing the domain description language on PDDL, we remain in the spirit of the existing programming competition, which we expect to help further bring the communities together. But, I like DBN representations. Is there some way for me to participate? Do not fear. The representation is sufficiently powerful to support a direct translation from the kind of conditional probability tables used in dynamic Bayesian network (DBN) representations (Dean & Kanazawa 1989), even if they include context-specific independence (Boutilier et al. 1996). For groups that have DBN-based planners and don’t feel they will be able to make drastic modifications, it is worth pointing out that there are techniques that make it possible to generate a DBN representation from a (propositionalized) STRIPS-like representation with only a polynomial increase in representation and plan size (Littman 1997). Was that a shameless plug? No, we’re a little ashamed. Since the domain description language is based on PDDL, does this mean the representation is relational? Yes, you’re very observant. Although representations with explicit objects are not a traditional feature of MDPbased domain description languages, algorithms that exploit these features have begun to appear. We expect that many groups will propositionalize the domains because they cannot directly plan with parameterized operators. Most of the test domains will allow for relatively straightforward propositionalization, so the relational representation should not be seen as an impediment to entry for interested groups. We simply feel that relational MDPs are an exciting direction worth supporting and want to give researchers interested in relational issues an opportunity to explore this type of representation. I don’t know how to write a parser for such an elegant, syntactically rich language. What resources will be available for me? Thank you, it is a nice language, isn’t it? We intend to provide software in C++ for a plan validator and very simple planner (essentially a parser). We are also considering