While strong cohesion within a routine is important, loose coupling is what we desire between routines. There are four criteria to use when evaluating coupling as shown in Figure 13. These criteria are applied to the various forms of coupling. Loose coupling occurs when the routines are low in size and high in intimacy, visibility, and flexibility. Routines can be coupled through data or control.
Table 13: Criteria for Evaluating Couplings
The levels of coupling refer to various ways data and control can be used (Figure 14). For example, normal couplings are preferred to data-structure coupling since the callee must ``know'' the structure and contend with the extra fields.
