How are coupling and cohesion related to modular design?

Answer 1

Ideally, modules will have low coupling and high cohesion. Coupling describes the strength of the connection between modules in a program. Loose (or low) coupling occurs when modules do not depend on other modules. One way to control this is by avoiding the use of global variables and reducing the number of variables that are passed between the modules. Another is to limit the depth of module calls (where a module calls another module, that then calls another module, and so on). Cohesion is a measure of how well a module accomplishes the module's purpose. High cohesion implies that all the module's internal statements serve to perform the module's (single) task. In order for modules to work together, there must be some connection between them. The nature of the connection is important because it determines the extent to which the modules are coupled. How are they connected? The best way to connect them is to pass the value of a local variable in one module to a second module through its parameter list. (A local variable is a variable that is defined within a module (not a parameter) is local to that module. The values of local variables are not available outside of the module in which they are declared unless they are passed. Local variables are reset to their default values once control leaves the module in which they are declared.) Another way to share information is through the use of global variables. (A variable that is defined outside of a module and that does not need to be passed to a module to be accessed by it is a global variable. Global variables retain their value once control leaves the module in which they are referenced. ) Because the value of a global variable can be changed by any module without passing, it increases the coupling between modules.