Some Design Transforms

Migration from procedural architecture to object oriented architecture is possible through design transformations. This paper initially provides a conceptual foundation for migration from procedural to object oriented software architecture for legacy software. Firstly, it relies upon a view of software life cycle, in which all software development is considered to be evolutionary activity with re-engineering/restructuring as an important process applied repeatedly on the artefacts of development at various stages in this evolution. Secondly, it introduces a novel approach of viewing a procedural program from an object oriented perspective in which there is a single god class which has a large number of global variables & methods, supported by several user defined classes which have no behaviour but data definitions. This view, coupled with repeated restructuring, enables a seamless migration of behaviour from the god class to other classes using design transformation methods. This paper distinguishes between the processes of translation and transformation and states that these two are orthogonal to each other, thus enabling us to concentrate on behaviour preserving design transformations to migrate from one design to another, leaving the language issues to be handled by translators. Having established the need for behaviour preserving design transformations, we provide a template for specifying design transformations. The main contribution of this paper is in the proposal of a template for the communication of design transformations. An example design transformation is presented which demonstrates the usefulness the template proposed in this paper.