Many existing software systems can benefit from restructuring to reduce maintenance cost and improve reusability. Yet, intuition-based, ad hoc restructuring can be difficult and expensive, and can even make software structure worse. We introduce a quantitative framework for software restructuring. In the framework, restructuring decisions are guided by visualized design information and objective criteria. The design information can be extracted directly from code to restructure existing or legacy software. Criteria for comparing alternative design structures include measures of design-level cohesion and coupling. Restructuring is accomplished through a series of decomposition and composition operations which increase the cohesion and/or decrease the coupling of individual system components. An example and a case study demonstrate the framework. The framework ensures that restructuring results in measurable improvements in design quality. Copyright © 1999 John Wiley & Sons, Ltd.

Cohesion was first introduced as a software attribute that, when measured, could be used to predict properties of implementations that would be created from a given design. Unfortunately, cohesion, as originally defined, could not be objectively assessed, while more recently developed objective cohesion measures depend on code-level information. We show that association-based and slice-based approaches can be used to measure cohesion using only design-level information. An analytical and empirical analysis shows that the design-level measures correspond closely with code-level cohesion measures. They can be used as predictors of or surrogates for the code-level measures. The design-level cohesion measures are formally defined, have been implemented, and can support software design, maintenance and restructuring.

Cohesion was first developed to predict properties of implementations created from a given design. Unfortunately, cohesion, as originally defined, could not be objectively assessed, while more recently developed objective cohesion measures depend on code level information. We show that association based and slice based approaches can be used to measure cohesion using only design level information. Our design level cohesion measures are formally defined, can be readily implemented, and can support software design, maintenance, and restructuring.