"standard" lifecycle. To a large extent, the same deliverables are one such method which is being used within the industry is KADS produced, albeit in a slightly different format. (KBS Analysis and Design Support). This is a methodology which The key deliverables in a formal methods development are the takes the user through the initial knowledge acquisition stages, initial specification of the system, the final design of the system and 25/8 Software systems in telecommunications Requirements Capture Aims and Objectives and Analysis User Requirements System Specification Specification Project Plan Quality Plan Design Level 1 Level 2 System Design Level N System Production Code and System System and Unit Tests Code and Unit Testing User Documentation Integration System Testing Installation Acceptance Testing Further Development Figure 25.2 Main stages in the software lifecycle, with deliverables the system itself. The initial specification is very important because of the system. These descriptions will also form the basis for testing this forms the basis for the whole development. the system, as they define what the system is meant to do. This initial specification is developed using an "invent and verify" Considerable effort is required to produce and verify these inter- paradigm. The specification is enriched (more details about the mediate descriptions. However, experience from other projects system is added) and refined (more details about how the system is shows that a corresponding amount of effort is saved in the coding to be implemented) to produce another description of the system. and testing stages of the lifecycle. This new description is then checked or verified against the initial Figure 25.2 shows the main stages in the lifecycles together with specification to ensure that this description is a "proper" develop- the main deliverables from each stage. More detailed information ment of the initial specification. may be found in Hughes (1992). There may be several intermediate descriptions of the syst