Subject-oriented design: Towards improved alignment of requirements, design and code

In practice, object-oriented design models have been less useful throughout the lifetime of software systems than they should be. Design models are often large and monolithic, and the structure of the designs is generally quite different from that of requirements. As a result, developers tend to discard the design, especially as the system evolves, since it is too difficult to keep its relationship to requirements and code accurate, especially when both are changing. This paper presents a different approach to designing systems, based on flexible decomposition and composition, that closely aligns designs with both requirements specifications and with code. We illustrate how this approach permits the benefits of designs to be maintained throughout a system's lifetime. © 1999 ACM.