M*-OBJECT is a methodology for the analysis, design and implementation of CIM information systems. In this paper, the conceptual design phase is presented. It starts from users information requirements and provides a conceptual specification, the conceptual schema, of the information system to be used in the integrated manufacturing system to be designed. This methodological phase is supported by the Process and Data Net (PDN) model which integrates an objet-oriented data model, a query and data manipulation language, a process model, and an object behaviour description model. The major features of the specification approach are : static, dynamic, and behavioural properties of information are fully covered, complex data structures and data manipulation can be specified, and specifications are executable for rapid prototyping.