Abstract: BOM (Bill of Materials) is a basic form of data exchange among different departments and processes in enterprise. Due to the diversity of requirements in various departments, there exist many kinds of BOM to meet their specific needs. Such a variety of BOM forms complicates the transfer of data and may also lead to inconsistency. This paper worked out some formal definition of basic concepts such as component relation, component constraint, and component configuration. Based on these definitions, a flexible way of defining BOM is given, through which the variety of BOM forms could be reduced. Although the definition is focusing on manufacturing enterprises, it can be easily extended and applied to other fields. In addition, some algorithms to solve the disagreement among different forms of BOM are also presented.