A Hybrid Model for Object-Oriented Software Maintenance
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An object-oriented software system is composed of a collection of communicating objects that co-operate with one another to achieve some desired goals. The object is the basic unit of abstraction in an OO program; objects may model real-world entities or internal abstractions of the system. Similar objects forms classes, which encapsulate the data and operations performed on the data. Therefore, extracting, analyzing, and modelling classes/objects and their relationships is of key importance in understanding and maintaining object-oriented software systems. However, when dealing with large and complex object-oriented systems, maintainers can easily be overwhelmed by the vast number of classes/objects and the high degree of interdependencies among them. In this thesis, we propose a new model, which we call the Hybrid Model, to represent object-oriented systems at a coarse-grained level of abstraction. To promote the comprehensibility of objects as independent units, we group the complete static description of software objects into aggregate components. Each aggregate component logically represents a set of objects, and the components interact with one other through explicitly defined ports. We present and discuss several applications of the Hybrid Model in reverse engineering and software evolution. The Hybrid Model can be used to support a divide-and-conquer comprehension strategy for program comprehension. At a low level of abstraction, maintainers can focus on one aggregate-component at a time, while at a higher level, each aggregate component can be understood as a whole and be mapped to coarse-grained design abstractions, such as subsystems. Based on the new model, we further propose a set of dependency analysis methods. The analysis results reveal the external properties of aggregate components, and lead to better understand the nature of their interdependencies. In addition, we apply the new model in software evolution analysis. We identify a collection of change patterns in terms of changes in aggregate components and their interrelationships. These patterns help to interpret how an evolving system changes at the architectural level, and provides valuable information to understand why the system is designed as the way it is.