1.6 Summary

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Networked application software has been developed manually from scratch for decades. The continual rediscovery and reinvention of core concepts and capabilities associated with this process has kept the costs of engineering and evolving networked applications too high for too long. Improving the quality and quantity of systematic software reuse is essential to resolve this problem.

Middleware is a class of software that's particularly effective at providing systematically reusable artifacts for networked applications. Developing and using middleware is therefore an important way to increase reuse. There are many technical and nontechnical challenges that make middleware development and reuse hard, however. This chapter described how object-oriented frameworks can be applied to overcome many of these chal-lenges. To make the most appropriate choice of software development technologies, we also described the differences between frameworks and class libraries, components , patterns, and model-integrated computing. Each technology plays a part in reducing software development costs and life cycles and increasing software quality, functionality, and performance.

The result of applying framework development principles and patterns to the domain of networked applications has yielded the ACE frameworks. These frameworks handle common network programming tasks and can be customized via C++ language features to produce complete networked applications. When used together, the ACE frameworks simplify the creation, composition, configuration, and porting of networked applications without incurring significant performance overhead. The rest of this book explains how and why the ACE frameworks were developed and shows many examples of how ACE uses C++ features to achieve its goals.

An intangible, but valuable , benefit of ACE is its transfer of decades of accumulated knowledge from ACE framework developers to ACE framework users in the form of expertise embodied in well- tested C++ classes that implement time-proven networked application software development strategies. These frameworks took scores of person- years to develop, optimize, and mature. Fortunately, you can take advantage of the expertise embodied in these frameworks without having to independently rediscover or reinvent the patterns and classes that underlie them.

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