Viewpoints as an evolutionary approach to software system maintenance

We describe a black box approach to software system evolution where viewpoints are used to alter a design without modifying the original system. A viewpoint is a model, possibly incomplete, of a domain from a given perspective. We discuss the views-an operator and its semantics, and then apply the concepts to the NACHOS file system as a case study. We believe the approach can be applied to existing object oriented software systems, and serve as a guide for developing systems which are more easily maintained. This case study is an example of an application of a more general transformational approach to software design and implementation