Introduction to extended common coupling with an application study on Linux

Common coupling is usually considered an obstacle to software maintenance. In this paper, we study the interaction of common coupling with other forms of software coupling and introduce the concept of extended common coupling. We define four types of extended common coupling, which can help us to understand how a global variable is usually referenced, and how it is related to other forms of coupling. We perform an application study on Linux global variable current. The result shows that in most cases, global variable current in Linux is used with stamp coupling instead of data coupling, which will make the maintenance more difficult.