Coupling

Meaning 1

Coupling is a measure for the strength of the dependencies between modules.

There are plenty of different types of couplings. These are the classic ones ordered from loose to tight¹⁾:

Type	Description	Justification
No coupling	The modules do not know each other.	good
Call coupling	A module calls another one.	good
Data coupling	A module calls another one passing parameters to it.	good
Stamp coupling	A module calls another one passing complex parameters to it.	good
Control coupling	A module influences the control flow of another module.	bad or OK
External coupling	The modules communicate using a simple global variable.	bad
Common coupling	The modules communicate using a common global data structure.	bad
Content coupling	A modules depends on the inner working of another module. This is the strongest form of coupling.	extremely bad

Up to control coupling they can be considered “good” couplings, although the lower the coupling the better (see Low Coupling).

Then there are also some special types of couplings:

Tramp Coupling	A module is only coupled to a data structure because some other module needs the data. The module gets the data and passes it to the other module without touching the “tramp data”²⁾	bad
Hybrid Coupling	A parameter (or return type) is data and control flow information at the same time.	partly bad
Logical Coupling	A module makes some assumptions about another module without referencing it. For example a module A only sorts a list because some other module B which A technically does not know about needs it sorted.	bad
Temporal Coupling		bad
Natural Coupling	A natural coupling is a coupling between classes which represent concepts which are dependent in the same way.	good
Artificial Coupling	An artificial coupling is a coupling which is only there for technical reasons.	bad
Abstract Coupling	A design pattern using	good

Discuss this wiki article and the term on the corresponding talk page.

¹⁾

see G. J. Myers: Reliable Software through Composite Design

²⁾

see M. Page-Jones: The Practical Guide to Structured Systems Design