Resumen
A framework is a generic application that allows the creation of different applications from an application domain. Due to the inherent flexibility and variability of a framework, framework design is much more complex than application design. Experience shows that the complexity of framework design is reduced by separating clearly different issues: the design of a class model for an application from the framework domain; the analysis and specification of the domain variability and flexibility; and its stepwise implementation by a sequence of generalizing transformations. Since application design is a well-known activity, the article will concentrate on the specification of the variable aspects, on the design of a local class structure that provides each with the required variability, and on how to transform a class structure for generalization. When developing a framework, don't plan all design activities in one development cycle. Framework development should be based on experience, nobody will develop a useful framework from scratch in one development cycle. Therefore, the design activities should be distributed over different development cycles.