STAN

(STate ANalysis) [Fox Long1999] extends the Graphplan algorithm in part by adding a preprocessor (called TIM) to infer type information about the problem and domain. This information is then used within the planning algorithm to reduce the size of the search space that the Graphplan algorithm would search. STAN also incorporated optimized data structures (bit vectors of the planning graph) that help avoid many of the redundant calculations performed by Graphplan. Additionally, STAN maintains a wave front during graph construction to track remaining goals and so limit graph construction. Subsequent versions incorporated further analyses (e.g., symmetry exploitation) and an additional simpler planning engine. Four versions of STAN were tested: the AIPS98 competition version, version 3.0, version 3.0s and a development snapshot of version 4.0.