Software Engineering (2160701)

Coupling

Cohesion

Classification of Coupling

Data coupling

• Two modules are data coupled, if they communicate through a parameter.
• An example is an elementary (primal) data item passed as a parameter between two modules, e.g. an integer, a float, a character, etc.

Stamp coupling

• This is a special case (or extension) of data coupling
• Two modules (``A'' and ``B'') exhibit stamp coupling if one passes directly to the other a composite data item - such as a record (or structure), array, or (pointer to) a list or tree.
• This occurs when Class B is declared as a type for an argument of an operation of ClassA

Control coupling

• If data from one module is used to direct the order of instructions execution in another.
• An example of control coupling is a flag set in one module and tested in another module.

Common coupling

• Two modules are common coupled, if they share data through some global data items.
• Common coupling can leads to uncontrolled error propagation and unforeseen side effects when changes are made.

Content coupling

• Content coupling occurs when one component secretly modifies data that is internal to another component.
• This violets information hiding – a basic design concept
• Content coupling exists between two modules, if they share code.

Classification of Cohesion

Coincidental cohesion

• A module is said to have coincidental cohesion, if it performs a set of tasks that relate to each other very loosely.
• In this case, the module contains a random collection of functions.
• It is likely that the functions have been put in the module out of pure coincidence without any thought or design.
• For Ex., in a transaction processing system (TPS), the get-input, print-error, and summarize-members functions are grouped into one module.

Logical cohesion

• A module is said to be logically cohesive, if all elements of the module perform similar operations.
• For Ex., error handling, data input, data output, etc.
• An example of logical cohesion is the case where a set of print functions generating different output reports are arranged into a single module.

Temporal cohesion

• When a module contains functions that are related by the fact that all the functions must be executed in the same time span.
• For Ex., the set of functions responsible for initialization, start-up, shutdown of some process, etc.

Procedural cohesion

• If the set of functions of the module are all part of a procedure (algorithm) in which certain sequence of steps have to be carried out for achieving an objective
• For Ex., the algorithm for decoding a message.

Communicational cohesion

• If all functions of the module refer to the same data structure
• For Ex., the set of functions defined on an array or a stack.

Sequential cohesion

• If the elements of a module form the parts of sequence, where the output from one element of the sequence is input to the next.
• For Ex., In a Transaction Processing System, the get-input, validate-input, sort-input functions are grouped into one module.

Functional cohesion

• If different elements of a module cooperate to achieve a single function.
• For Ex., A module containing all the functions required to manage employees’ pay-roll exhibits functional cohesion.