8. Yourdon Systems Method (YSM). （8。）.pdfVIP

Chapter 8 – Yourdon Systems Method (YSM) Notes 8. Yourdon Systems Method (YSM). 8.1. Introduction This chapter gives a brief outline of the 1993 version of the method. Unlike earlier versions, YSM now uses terms like real-world and subject-matter when talking about systems modelling. It is to be wondered how much these changes have been influenced by the work of Michael Jackson whose JSD method (1983) used these notions to escape from the limitations of top-down development. For a full coverage see the book Yourdon Systems Method, by Yourdon Inc. Originally, YSM was very similar to STRADIS (see Chapter 9), Yourdon, Gane and Sarson all being one-time colleagues. However, unlike STRADIS, YSM in its later versions has attempted to move away from pure functional decomposition towards something called event partitioning which is claimed to be neither top-down, nor bottom-up but ‘middle-out’. However, because the method still uses the time-honoured techniques of data-flow diagrams and entity-relationship models it is difficult to see how the shackles of functional decomposition have been shed. YSM now claims to be a third generation method. However, we must note the essential difference between YSM and JSD (another 3GM) which is that unlike YSM, the Jackson approach has eschewed completely any notion of functional decomposition. The method requires the analyst first to draw a context-diagram (top level