What is Modularity Theory?

Modularity Theory (or the Theory of Interdependence and Modularity) explains how different parts of a system’s architecture relate to one another and consequently affect the development and adoption of that system.

According to the theory, a system’s architecture determines its components and systems and defines how they must interact—fit and work together—in order to achieve desired outcomes.

The place where any two subsystems fit together is called an interface. A system’s architecture is interdependent at an interface if one part can’t be created independently of the other. In other words, the way one is designed and made depends on the way the other is designed and made. Unpredictable interdependencies require the same person, team, or organization to simultaneously develop both components for the overall system to work.

In contrast, a modular interface is one in which there are no unpredictable interdependencies between subsystems, people, teams, or organizations. Modular components and subsystems fit and work together in well-understood and highly-defined ways. A modular system architecture specifies the fit and function of all elements so completely that it doesn’t matter who makes the components or subsystems, as long as they meet specifications. In other words, to the extent that interfaces are specifiable, verifiable, and predictable, they are modular in nature. Systems that rely on modular interfaces allow people in separate teams or organizations to do their work with little to no effort spent on coordination.