$${\rm I}.\,\,\,\,\,\,\,\,\,\,\,$$ Content coupling
$${\rm II}.\,\,\,\,\,\,\,\,\,$$ Common coupling
$${\rm III}.\,\,\,\,\,\,\,$$ Control coupling
$${\rm IV}.\,\,\,\,\,\,\,$$ Stamp coupling
$${\rm V}.\,\,\,\,\,\,\,\,\,$$ Data coupling
Coupling between modules can be ranked in the order of strongest (least desirable) to weakest (most desirable) as follows.
$${\rm I}.\,\,\,\,\,\,$$ The cyclomatic complexity of a module is equal to the maximum number of
$$\,\,\,\,\,\,\,\,\,\,\,$$linearly independent circuits in the graph.
$${\rm II}.\,\,\,$$ The cyclomatic complexity of a module is the number of decisions in the
$$\,\,\,\,\,\,\,\,\,\,$$module plus one, where a decision is effectively any conditional statement in
$$\,\,\,\,\,\,\,\,\,\,$$the module.
$${\rm III}\,$$ The cyclomatic complexity can also be used as a number of linearly
$$\,\,\,\,\,\,\,\,\,\,$$independent paths that should be tested during path coverage testing.
$${\rm I}.\,\,\,\,\,\,$$ The content diagram should depict the system as a single bubble.
$${\rm II}.\,\,\,\,$$ External entities should be identified clearly at all levels of $$DFDs$$
$${\rm III}.\,\,$$ Control information should not be represented in $$DFD$$
$${\rm IV}.\,\,$$ A data store can be connected either to another data store or to an external
$$\,\,\,\,\,\,\,\,\,\,\,\,$$entity.