Focus Issue on Legacy Information Systems and Business Process Change: Migrating Large-Scale Legacy Systems to Component-Based and Object Technology: The Evolution of a Pattern Language

The process of developing large-scale business critical software systems must boost the productivity both of the users and the developers of software, while at the same time responding flexibly to changing business requirements in the face of sharpening competition. Historically, these two forces were viewed as mutually hostile. Component-based software development using object technology promises a way of mediating the apparent contradiction. This paper presents a successful new approach which focuses primarily on the architecture of the software system to migrate an existing system to a new form. Best practice is captured by software patterns that address not only the design, but also the process and organizational issues. The approach was developed through four completed, successful live projects in different business and technical areas. It resulted in a still-evolving pattern language called ADAPTOR (Architecture-Driven and Pattern-based Techniques for Object Re-engineering). This article outlines the approach that underlies ADAPTOR. It challenges popular notions of legacy systems by emphasizing business requirements. Architectural approaches to migration are then contrasted with traditional reverse engineering approaches, including the weakness of reverse engineering in the face of paradigm shifts. The evolution of the ADAPTOR pattern language is outlined with a brief history of the projects from which the patterns were abstracted