Contractor and purchaser: do they think about the same system during project implementation?

The paper discusses the problems of purchaser and contractor coordination during design and implementation of interdisciplinary and complex CBS (computer based systems) projects, and the roles of system engineering teams (SET) in CBS design and implementation. This paper describes the process of CBS design and implementation, from the beginning of the project when the purchaser defines his requirement through, to the definition of technical requirements, design, verification, and deployment of CBS. Additionally, the typical organization of a large purchasing company and the role of the SET during the project implementation is discussed. A survey of projects and author experience shows that the potential for a widening expectation gap during project implementation between the purchaser and the contractor arises from misunderstandings of the CBS purpose. The question that is discussed in this paper is "Do purchasers and contractors think about the same system during project implementation?". The paper analyses the main problems that cause the gap, the actions that could be carried out to "bridge the gap", and the role of the SET to overcome any misunderstandings between the purchaser and the contractor.