The analysis of planning systems in terms of the different algorithms they use needs to be complemented by a study of how these systems represent and use available knowledge -- in other words, of their problem-solving methods. The goals of such knowledge level analysis are complementary to that of algorithms: instead of finding which algorithm is the most efficient, we can find the role of each piece of knowledge in the system. This is an essential aspect in finding out how to engineer a planning system and obtain a desired performance in an application and its engineering. One analysis of this type has been made. However, that analysis was incomplete, because it concentrated on the organization of the domain knowledge used by the system. Another equally important aspect is the way this knowledge is used in the planning process. These two are complementary aspects in the description of a problem-solving method. In this paper, we will depart from and complement Valente’s analysis by providing a more detailed discussion on planning tasks, providing a general, high-level task. decomposition for planning.