The role and impact of assumptions in software development, maintenance and evolution.

This paper discusses the gradual invalidation of assumptions explicitly or implicitly embedded in software and shows this is an inevitable, probably dominant, cause and driver of software evolution. It reasons that such evolution is a natural phenomenon having major safety, reliability and economic impact on computer usage. In the context of growing computer application, the phenomenon and its significance as this technology is ever more widely exploited are becoming increasingly apparent. Many evolution properties identified are also present elsewhere but their impact is more profound in the field of software development, application and maintenance than in other fields.