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 of ten large and monolithic, and the structure of the designs is generally qui te different from that of requirements. As a result, developers tend to dis card the design, especially as the system evolves, since it is too difficul t to keep its relationship to requirements and code accurate, especially wh en both are changing. This paper presents a different approach to designing systems, based on flexible decomposition and composition, that closely ali gns designs with both requirements specifications and with code. We illustr ate how this approach permits the benefits of designs to be maintained thro ughout a system's lifetime.