Hierarchical Understandability Assessment Model for Large-Scale OO System

Understanding software, especially in large-scale, is an important issue for software modification. In large-scale software systems, modularization provides help for understanding them. But, even if a system has a well-modularized design, the modular design can be deteriorated by system change over time. Therefore it is needed to assess and manage modularization in the view of understandability. However, there are rarely studies of a quality assessment model for understandability in the module-level. In this paper, we propose a hierarchical model to assess understandability of modularization in large-scale object-oriented software. To assess understandability, we define several design properties, which capture the characteristics influencing on understandability, and design metrics based on the properties, which are used to quantitatively assess understandability. We validate our model and its usefulness by applying the model to an open-source software system.