Abstract :
Summary form only given. The paper briefly refers to a number of the, by now well known, results of the author´s studies of software evolution since they provide a basis and framework for the development of a theory of the phenomenon. The author then summarises his most recent results outlining a proof that every E-type program reflects an unbounded number of assumptions about the application implemented, supported or modelled by the program. He shows that the presence of such assumptions is inevitable and that some of these become invalid over time as a consequence of changes in the dynamic real world. Some of the finite set of known assumptions reflected in the program is also become invalid. Together the resultant ever extending invalidity causes the software to require continuing change or to become ever more unsatisfactory or even invalid. This phenomenon provides the underlying and unavoidable cause of the universal experience that E-type software must be continually evolved to remain satisfactory and suggests that its further study and the development of methods and tools to reduce its considerable impact, economic and social cost, must form an important part of future software engineering R & D.
