Prodigy is able to do hierarchical planning, by selecting an appropriate abstraction hierarchy. The planner uses the ALPINE abstraction module to build a series of abstract solutions to problems. The abstraction hierarchy is traversed and increasingly detailed plans built during this traversal. Thus the approach Prodigy uses is top-down, which the authors contend produces more elegant and concise plans than an opportunistic (bottom-up) approach.
The planner uses the definition of a problem as an initial state and a goal state(s). Then the planning/problem solving module, directed by knowledge from ALPINE, traverses the search space at each level in the abstraction hierarchy. When a solution is found, the plan is refined at the next lower level as described above.
Go to a discussion of this capability for multiple architectures.