Decomposition and reduction of packet set

Packet set is a set pair which is composed of the internal and outer packet set together. In this paper using the concepts and structures of packet set, we give several new concepts, such as decomposition class, reduction class, decomposition base, reduction base and so on. We further put forward decomposition and reduction theorem, the maximal and minimal attribute set principles. Decomposition and reduction of packet set are the theoretical base in the research of reasoning in dynamic system.