Coupling , Cohesion and there Types

What is Coupling and Cohesion.
Types of Cohesion
Types of Coupling
Logical , Temporal , Procedural , Sequential Cohesion
Content , Common , Control, Data Message , No Coupling

1. Cohesion In computer programming, cohesion refers to the degree to which the elements of a module belong together. Thus, cohesion measures the strength of relationship between pieces of functionality within a given module. For example, in highly cohesive systems functionality is strongly related. Cohesion is an ordinal type of measurement and is usually described as “high cohesion” or “low cohesion”.

2. Logical cohesion Logical cohesion is when parts of a module are grouped because they are logically categorized to do the same thing even though they are different by nature (e.g. grouping all mouse and keyboard input handling routines).

3. Temporal cohesion Temporal cohesion is when parts of a module are grouped by when they are processed - the parts are processed at a particular time in program execution (e.g. a function which is called after catching an exception which closes open files, creates an error log, and notifies the user).

4. Procedural cohesion P r o c edu r al c ohesi o n i s w hen parts of a mo d ul e a r e grouped because they always follow a certain sequence o f e x ecu t i o n (e . g . a func t i o n w hich check s f ile permissions and then opens the file).

5. Commun i c a tion a l/i n f orm a tion a l cohesion Communicational cohesion is when parts of a module are grouped because they operate on the same data (e.g. a module which operates on the same record of information).

6. Sequential cohesion Sequential cohesion is when parts of a module are grouped because the output from one part is the input to another part like an assembly line (e.g. a function which reads data from a file and processes the data).

7. Functional cohesion (best) Functional cohesion is when parts of a module are grouped because they all contribute to a single well- defined task of the module (e.g. Lexical analysis of an XML string).

8. While f u n ctio n al c ohesi o n is c o n si d e r e d th e mo s t desirable type of cohesion for a software module, it may not be achievable. The r e a r e cases w he r e c o mm unicati o na l c ohesi o n i s th e h i g hest l e v e l of cohesion that can be attained under the circumstances.

9. Examples of Cohesion

10. C OUPLING

11. Coupling (computer programming) In software Engenering , coupling is the degree of interdependence between software modules; a measure of how closely connected two routines or modules are; the strength of the relationships between modules. Coupling is usually contrasted with cohesion . Low coupling often correlates with high cohesion, and vice versa. Low coupling is often a sign of a well- structured computer system and a good design, and when combined with high cohesion, supports the general goals of high readability and maintainability.

12. Content coupling (high) Content coupling (also known as Pathological coupling ) occurs when one module modifies or relies on the internal workings of another module (e.g., accessing local data of another module). In this situation, a change in the way the second module produces data (location, type, timing) might also require a change in the dependent module.

13. Example of Content coupling

14. Common coupling Common coupling (also known as Global coupling ) occurs when two modules share the same global data (e.g., a global variable). Changing the shared resource might imply changing all the modules using it.

15. Example of Common coupling

16. Control coupling Control coupling is one module controlling the flow of another, by passing it information on what to do (e.g., passing a what-to-do flag).

17. Example of Control coupling

18. Stamp coupling (Data-structured coupling)   In this type of coupling, the data structure is used to transfer information from on component to another.

19. Example of Stamp coupling

20. Data coupling  The modules are connected by the data coupling, if only data can be passed between them.

21. Example of Data coupling

22. Message coupling (low) This is the loosest type of coupling. It can be achieved by state decentralization (as in objects) and component communication is done via parameters or message passing .

23. Example of Message coupling

24. External coupling External coupling occurs when two modules share an externally imposed data format, communication protocol, or device interface. This is basically related to the communication to external tools and devices.

25. Example of External coupling

26. No coupling Modules do not communicate at all with one another.

27. Example of No coupling