In the development of a software environment for integrated design and manufacturing of machines, the relevance of conceptual data modelling becomes apparent. This paper presents an analysis of the applicability of some notions of conceptual data modelling in the current literature, based on our experience in modelling for CAD of machines. The notions to be examined are: object relativity, object reliability, object convertibility, Functional dependency, derived attribute and composite object. Some notes and proposals for extending those notions to meet new requirements from engineering design are also presented. To stimulate the application of database technology in engineering the examples have been taken from the machine design domain as much as possible. The paper may also provide some guidelines For conceptual data modelling.