The instability of software projects: The role of private and public components

Software architecture expresses how the initial concept of a software system has been actually implemented. However, requirement changes imply the continuous modification of the software system and can impact its architecture. The paper analyses how the architecture instability of a software system evolves during its life cycle and investigates which kind of change, in terms of classes added, removed, and modified, influences more the software system instability. The access control modifiers of the methods and instance variables of the modified classes are then analyzed for understanding which kind of members, among the public or private ones, are most frequently added or removed.