One of the major problems in information technology is how to specify a system satisfactorily. The specification occupies a key position in the information system development life-cycle, concerning the relationship between the client and the system engineer, as well as many subsequent relationships during the design, coding and maintenance levels of information systems development. In this paper the major concept presented is that a formal model of information system specification is a vital nucleus around which subsequent layers of system development and categorisation of the information system can be performed accurately, unambiguously and to the best satisfaction of all users of the designed system.