n The logical components of the design should correspond to physically separate syntactic software components. n Modules should be self-contained and coherent. n Cohesion is a measure of the degree to which a module completely encapsulates a single notion (a facet of the system’s functionality or data). n Coupling is a measure of the degree to which a module interacts with and depends on other modules. n We want to design modules with high cohesion and weak coupling.