11.10 Exercises 259
O-Plan, SIPE-2, and SHOP2 can each do certain kinds of temporal planning. For
details, see the web sites for O-Plan and SIPE-2, and see Nau et al. [413] for SHOP2.
Advantages and Disadvantages. Compared with classical planners, the primary
advantage of HTN planners is their sophisticated knowledge representation and
reasoning capabilities. They can represent and solve a variety of nonclassical plan-
ning problems; with a good set of HTNs to guide them, they can solve classical
planning problems orders of magnitude more quickly than classical or neoclassical
planners. The primary disadvantage of HTN planners is the need for the domain
author to write not only a set of planning operators but also a set of methods.
Comparing HTNs