Saz: Ssadm Version 4 and Z

1 Overview of the SAZ Method SAZ 1, 3] is an integrated method developed at the University of York 1. The method takes a diagram-and-text speciication and develops a formal description of (Z) state and operations. SAZ was originally developed 4] for use with SSADM version 4, and has been shown to raise issues which are not traditionally apparent in systems analysis and design 5]. SAZ and SSADM SSADM version 4 6, 7] and its subsequent variants form the UK de facto standard for information systems development. The method is best suited to complex, multi-analyst projects. However, the philosophy of SSADM version 4 is adaptation, and it is thus possible to apply selected parts of the method to much smaller information systems, such as these case studies. SSADM version 4 provides a development structure, and suggested diagram-and-text techniques. SAZ uses SSADM Requirements Speciication (RS). This is derived from a Requirements Analysis (RA) which extracts and clariies requirements using high-level data and functional models. RS speciies an abstract system to meet the requirements using data, dynamic and functional models. SSADM includes minimal cross-checking among its models; constraints (dynamic and static) are not routinely recorded. The rst task of the developer is to determine which parts of the method are appropriate for a project. The RA techniques used on the case studies comprise an entity-relationship diagram with simple documentation and a logical data ow diagram (DFD). Using the SSADM RS techniques, the data model is then validated against the scope of the system. The data ow diagram is reworked to function deenitions. These, rather than the DFDs, are the speciication of system processing. Function deenitions are text descriptions of the processing required of the system, and are derived by identifying system events and tracing their eeects through the DFD. SSADM advises that the results are referred to client users, who may combine, divide or replicate the functions. The RS also considers the dynamics of each entity, using entity life histories (ELHs). The case studies use the notations suggested (but not mandated) by SSADM version 4. The speciications are developed sequentially through the chapter.