An Intentional View of Change
Résumé
System evolution is a fact of industrial life. In order to survive in a more and more competitive environment, organizations undergo frequent changes that imply changes of their software based systems. As a consequence of the fast speed of organizational change, system evolution costs are far higher than initial development costs. Handling system evolution has therefore been and is still, an important issue that we consider in this talk. Our position is that a prerequisite to perform software change is to understand the way organizational changes impact system requirements. Just as for systems developed from scratch where requirements elicitation provides a basis for subsequent software design and implementation, changes in design and implementation are rooted in changed requirements. Eliciting these change requirements is the first concern of this talk: we express change requirements with gaps and similarities. Gaps are operators that express transformations of As-Is models into the To-Be models, whereas similarities specify through predicates what the As-Is and To-Be models shall have in common. The talk will present generic typologies of gaps and similarity measures and illustrate their instantiation for a goal driven representation formalism called MAP. It is also important to establish that the 'whys' of the system to be developed fit the 'whats' of the delivered system. The aim is to ensure a 'best fit' between organization needs (whys) and system functionality (whats). However, systems, once developed, undergo changes and it is of prime importance that the changed need and the changed system functionality continue to preserve the 'best fit'. The second part of the talk will consider the issue of co-evolution i.e. the coherent evolution of two interrelated entities, namely the software system and the business needs. The position adopted is again to express change requirements as gaps between As-Is and To-Be models expressing intentionally the alignment links between the business and the system.