Knowledge discovery in database have been attracting a significant amount of research, industry attention in recent years. Process planning knowledge (PPK) is one of the most important knowledge in mechanical manufacturing enterprise. The traditional method of turning data into knowledge relies on manual analysis and interpretation. This paper analyzes the source and composing of process planning knowledge and state of arts on process planning discovery in mechanical manufacturing enterprise. On the basis of the widely application of computer aided process planning (CAPP) system in mechanical manufacturing enterprise, the concept of process planning knowledge discovery (PPKD) is proposed based on process planning databases. This paper provides an overview CAPP database of the field, clarifying how PPKD in CAPP database are related both to each other and to related fields, the technology architecture of process planning knowledge discovery is founded based on objectoriented model-driven...