A new method is presented for representing machined surfaces, machining operations, machine tools and cutting tools according to the definitions of design and manufacturing primitives. A conjugative coding system is achieved through a new concept termed as conjugative concept. The codes provided by this system are not the classification codes. They are computer internal definition of relations between design and manufacturing which integrate design and manufacturing information into a compact data format. There are two significances of the codes. One is that the codes can represent directly design entities from CAD geometrical models. The other is that the codes replace the logics and rules built in automatic manufacturing systems to support the decision-making. This will provide the possibility of developing a single database (SDB) for a computer automated manufacturing system, which has been proposed to solve the problem of integration between CAD, CAPP and CAM systems