HP Labs Technical Reports

Experience With the ET++ Application Framework

Shaw, Robert; Young, Doug



Abstract: New software applications are often expected to share a set of common features with other applications. One example is the appearance and behavior of the application's user interface. Since the majority of development time for an application can be spent meeting an interface standard that, by definition, constrains the interface to resemble those of other applications within the same environment, code reuse is an important tool for the application developer. Object-oriented application frameworks are an effective reuse tool that mimics a common mode of informal code reuse, duplication and modification of an existing application. A framework supplies both a set of reusable components and a prototypical application skeleton to be used as a base for modification. We have ported an existing application framework, ET++, to the HP 9000/300 series of computers to gain experience with an object-orient ed application framework. ET++ fell short of our expectations, but supplied us with lessons on how an application framework should be built. The lessons usually involved common common sense issues in system building such as promul- gating a simple system model and creating and adhering to absractions. Some of the lessons were not so obvious. For instance, we found that inheritance alone does not solve the problems of extensibility in an object- oriented system, nor is it reasonable to assume that a class library designed for a language like Smalltalk will be appropriate to a system written in C++/

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