In many planning domains, it is impossible to construct plans that are guaranteed to keep the system completely safe. A common approach is to build probabilistic plans that are guaranteed to maintain system with a sufficiently high probability. For many such domains, bounds on system safety cannot be computed analytically, but instead rely on execution sampling coupled with a plan verification techniques. While probabilistic planning with verification can work well, it is not adequate in situations in which some modes of failure are very rare, simply because too many execution traces must be sampled (e.g., 1012) to ensure that the rare events of interest will occur even once. The P-CIRCA planner seeks to solve planning problems while probabilistically guaranteeing safety. Our domains frequently involve verifying that the probability of failure is below a low threshold (< 0.01). Because the events we sample have such low probabilities, we use Importance sampling (IS) (Hammersley and Handscomb 1964; Clarke and Zuliani 2011) to reduce the number of samples required. However, since we deal with an abstracted model, we cannot bias all paths individually. This prevents IS from achieving a correct bias. To compensate for this drawback we present a concept of DAGification to partially expand our representation and achieve a better bias.

The Association for the Advancement of Artificial Intelligence, in cooperation with Stanford University's Computer Science Department, was pleased to present its 2006 Spring Symposium Series held March 27-29, 2006, at Stanford University, California.

The Association for the Advancement of Artificial Intelligence, in cooperation with Stanford University's Computer Science Department, was pleased to present its 2006 Spring Symposium Series held March 27-29, 2006, at Stanford University, California. The titles of the eight symposia were (1) Argumentation for Consumers of Health Care (chaired by Nancy Green); (2) Between a Rock and a Hard Place: Cognitive Science Principles Meet AI Hard Problems (chaired by Christian Lebiere); (3) Computational Approaches to Analyzing Weblogs (chaired by Nicolas Nicolov); (4) Distributed Plan and Schedule Management (chaired by Ed Durfee); (5) Formalizing and Compiling Background Knowledge and Its Applications to Knowledge Representation and Question Answering (chaired by Chitta Baral); (6) Semantic Web Meets e-Government (chaired by Ljiljana Stojanovic); (7) To Boldly Go Where No Human-Robot Team Has Gone Before (chaired by Terry Fong); and (8) What Went Wrong and Why: Lessons from AI Research and Applications (chaired by Dan Shapiro).