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Typed Preconditions

Keywords: NONLIN, PLANNER, POPLER, STRIPS, preconditions

Categories: Planning

Author(s): Austin Tate

In early problem solving systems (e.g., STRIPS ) and planning languages (e.g., PLANNER) the operators were given a single set of preconditions which were always interpreted as `test if true, or subgoal to make them true'. The need to distinguish between the case in which the planner should only check if something was already true or should be allowed to add further actions into a plan to make the condition true was recognised as an important search control mechanism in POPLER. This led to two different types of precondition. Additions were also made to various pattern directed invocation systems which clustered alternative methods together and made a choice from them on the basis of some pre-occurring fact. The utility of typed preconditions and their different properties for both hierarchic domain description and planner Search Space control was investigated in the NONLIN planner which recognised four precondition types: SUPERVISED, UNSUPERVISED, USEWHEN and ACHIEVE.



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