Completeness versus usefulness in .NET Build Code 128A in .NET Completeness versus usefulness

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13.5 Completeness versus usefulness use none none printer tomake none with none Microsoft Office Development. Microsoft Office 2000/2003/2007/2010 In this book w none for none e have tried to position design as the central activity in software development. We have tried to show that it is possible to construct precise design models at various levels of abstraction, including models that come close to being and perhaps are complete descriptions of implementation behaviour. The time has.

7But note our comments in the next section on completeness. 13.5 Completeness versus usefulness come to consid none for none er whether it is appropriate and useful to build models that even approach the level of completeness we have suggested. Producing a complete implementation model, with full statecharts showing all interobject message sending, takes a considerable time. In the absence of tools to execute such models directly, we must decide whether it is worth spending that time when it is inevitable that another model at roughly the same level of abstraction will be produced in some other language, such as C++ or Smalltalk.

These languages are complex in their own right and, when coupled with the complexity of operating system interfaces and so on, the result must be a significant proportion of the developer s time spent on realising an implementation. Given the tools available at the time of writing in 1994, it is our contention that completeness is not often a reasonable goal in software design. For any system of moderate complexity, a complete design specification (complete in the sense that it leaves nothing unsaid) would take too long to create and be of limited use since it cannot be executed.

At heart, software development is actually about building executable systems, systems that work and are useful. We believe, and the evidence supports this view, that as soon as the system being built exceeds the trivial, any time spent on analysis and design activities is repaid during coding and subsequent system extension. But this does not imply that analysis and design must be exhaustive.

It is, of course, a trade-off. If we were to plot the total effort expended on a development project against the percentage of that time spent on analysis and design, we predict that the graph would be like the one shown in figure 13.8 (not to scale).

Although the shape of the curve will vary, according to such factors as the expected life-time of the software and the organisational culture, we think the principle is sound: there comes a point where spending extra time on analysis and design just cannot be justified. It is probably impossible to say where that point is without detailed consideration of the project in hand. From our own experience we know that this point is frequently exceeded.

Completeness and usefulness are not related. A few, scruffy diagrams showing the basis of operation of a system are frequently life-savers. The best guideline we can give is this: if you reach a point where you believe, on the basis of some real experience, that, given the current state of knowledge, the software can be completed in a satisfactory way, and that the amalgamation of the software with the analysis and design documents produced so far is sufficient to allow the system to be repaired and enhanced, don t spend any more time on your design models.

Hopefully, in time the software industry will develop tools that allow efficient execution of specifications. But even in 1994, we believe that a deep understanding of the design principles described in this book will empower designers to produce more elegant systems, and that the rigorous notations will provide a mode of communication between designers..

The development process 100%. Total effort Percentage of time spent on analysis and design Figure 13.8 The effort/design trade-off 13.6 Summary. At present, so ftware design is a creative and chaotic process performed by skilled and experienced craftsmen. It is necessary to separate clearly the software management process from the software design process, so that designers are not constrained by the formality needed by managers. The management process must be rigid and disciplined but not based on measurement of the use of design techniques.

The management process should establish milestones that correspond to the delivery of functioning code and achieve them in a series of evolutionary cycles. The ultimate goal of a software development organisation must be to establish an environment that reacts to changes in need by accommodating the need within the existing software framework, rather than meeting each set of needs with a separate project. Every development should have a small core team consisting of a project manager, a chief designer, assistant designers and a project administrator.

The core team takes full technical responsibility for the development. There are three major development activities: project preparation, construction and approval. The design process has as its aim systematic design, a condition where the code is at all times a consequence of the design models, and not the other way around.

It is inevitable that some design decisions can be made only by experimentation with implementations. The issue is how these experiments, or prototypes, are incorporated into the development process. We discuss two approaches: incremental prototyping, where each experiment is part of the system being developed, and dual-track design, where the results of the experiments are input to the design of the final system.

Neither approach guarantees systematic design, although dual-track design is more likely to provide it..
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