The term Planning is not used in Operations Research in the sense that is most common in Artificial Intelligence. AI Planning does have many features in common with OR scheduling, sequencing, routing, and assignment problems, however. Current approaches to solving such problems can be broadly classified into four areas: Combinatorial Optimization, Integer Programming, Constraint Programming, and Local Search. These areas have developed somewhat independently; they have characteristic strengths and weaknesses, and have been commercially developed to varying degrees.
In Constraints and AI Planning: Papers from the AAAI Workshop, Alexander Nareyek, ed., Technical Report WS-00-02 (AAAI Press, 2000) 1-6.