Chapter 6 VB/Access Programming

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Information Systems Developers HandbookProcedural programming techniques allow for the development of code with a highlevel of cohesion and loose coupling. A high level of cohesion means that eachsection of code (a subprogram or a function) processes only one task. This sectionof code may be called whenever that particular task is required, thus encouragingthe reuse of code.Traditional Procedural ApplicationMenuOption 1Option 2Option 3Loose coupling is achieved by using local variables and passing data betweensubprograms and functions whenever that data is required in another program,rather than declaring that data as global data. The drawback with global data is thatit is difficult to track the value of that data at any specific instance. Judicial use ofarguments passed between subprograms and functions allows for better tracking ofdata values. This is particularly so when data is passed by value from one sub toanother. These techniques also allow for the efficient reuse of code.6.6 Event Driven Programming TechniquesThe main feature of event driven programming is that the control does not follow apredetermined path. An event may be triggered by the system, other applications,or by the user actions. For example:• system timer• user actions command buttonmouse movekey stroke• application load formThe sequence of events determines the sequence of code execution. Typically thesequence of events changes each time the application is run. This allows for greaterflexibility in the utility of these applications and is a major contributor to thePage 72
Chapter 6VB/Access Programmingincreased ‘user-friendliness’ of modern applications. However, from aprogrammer’s viewpoint, it adds complexity to the design of the application. As thesequence of events cannot be predicted, the application must make assumptionsabout the ‘state of the world’ when it executes. The programmer must structure theapplication so that these assumptions are always valid. For example, if anassumption is made that the user will have made an input to an entry field, the codemust ensure that input has been made before the event can occur. In suchcircumstances, a check must be included to ensure the data has been entered beforeallowing the event to proceed.The application shown in the figure, ‘Event-driven Procedural Application’ consistsof identical processes to the application shown in the previous figure, ‘TraditionalProcedural Application’. However in the event-driven application there aremultiple possible entry points and the user may choose any of these entry points atrandom. Each of the entry points represents an event.Event-Driven Procedural ApplicationEvent 12Event 21Opt io n 1MenuEvent 3 Event 4Opt ion 2Opt io n 3Page 73
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