The goal of this work is to devise a structured representation of manufacturing planning that captures both the sequence of processing steps and the data functions, such as tooling, fixturing, and setups. The difficulty in accomplishing this is that although processing steps are often strongly ordered, these steps do not follow neat functional boundaries between tools, fixtures, setups, etc. The solution presented in this paper is a matrix architecture for process planning (MAPP) which captures a sequence of planning phases that cut across functional boundaries while still allowing data to be organized neatly into major functions. The matrix itself is a set of data blackboards: the rows of the matrix are the sequence of planning phases, the columns are data functions, such as tools, fixtures, and setups. This architecture combines advantages of sequential architectures and blackboard architectures, and enables more accurate modeling of the interwoven nature of tooling, fixturing and setup decisions in manufacturing planning.