esentation (SD:/PR). These are 2. The software team has not got a strong mathematical back- equivalent in that they share a common semantics. Figure 25.1 ground. illustrates some of the elementary symbols. Process counter FPAR manager total:=0 enable disable alarm count count(total) TO manager total: =0 enable disable alarm count total:= total+1 count(total) TO manager total:=0 Figure 25.1 Some of the symbols used within SDL Lifecycle for each software design technique 25/7 25.3.3 Object oriented methods through analysis and design, and provides a basis from which to begin coding. Relatively recently it has been discovered that defining real world objects, and converting them into a software representation can 25.3.4.1 provide a way of producing reusable software components which are very much tailored to the problem domain. A software "object" is a set of data together with its access and transformation code or The following is reproduced from Hayball (1992) by kind per- mission of the authors: "Methods". A user of an object merely needs to know how to invoke the appropriate method; all object internals, for example data de- tails, are hidden. The term 'knowledge-based system' (and related terms such as 'expert system', as well as the broader area of 'artificial intel- In many areas the productivity gains through using object oriented ligence') has been surrounded by unnecessary confusion and ambi- languages have been significant. Object oriented methods to sup- guity. One reason for this is that the subject is an evolving and port this approach are being developed, and a number of notations complex area. The complexity primarily derives from the definition exist. The main method supporting Object Oriented Design (OOD) is HOOD, for which a number of tools are available. However, the of 'knowledge', but also from the breadth of coverage of such methods to support the full analysis and design phases are still being systems. Thus pragmatically, we define: developed. The most commonly known analysis and design metho