During the 1950’s, era of computing, computer programs were created using ad hoc software development approach; each system a unique, custom-built intellectual product. In their book, & Design, Edward Yourdon and Carl Argila state “There was no concept of reusability, interchangeability of parts, or for that matter, formal design.” The systems were difficult to maintain or enhance, and became more and more difficult with each change. During the 1960’s, there were efforts to create more maintainable software, and in a more predictabl ....