An abstract method for extracting goal orderings

Extracting and using goal orderings is a way to improve efficiencies of planning algorithms. During extracting goal orderings, some of existing methods can only deal with atomic goals of a specific problem that will introduce too much redundant work, and the others deal with predicates of a planning domain that can not extract enough goal orderings. The paper addressed an abstract method to extract goal orderings. The method used unification to identify different instantiations of a predicate when dealing with predicates. It can not only reduce redundant work during extracting, but also get enough goal orderings.