Difference between coupling and cohesion in software engineering ppt

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., the set of functions defined on an array or a stack.

If all functions of the module refer to the same data structure.

For Ex., the algorithm for decoding a message.

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 set of functions responsible for initialization, start-up, shutdown of some process, etc.When a module contains functions that are related by the fact that all the functions must be executed in the same time span.An example of logical cohesion is the case where a set of print functions generating different output reports are arranged into a single module.For Ex., error handling, data input, data output, etc.A module is said to be logically cohesive, if all elements of the module perform similar operations.For Ex., in a transaction processing system (TPS), the get-input, print-error, and summarize-members functions are grouped into one module.It is likely that the functions have been put in the module out of pure coincidence without any thought or design.In this case, the module contains a random collection of functions.A module is said to have coincidental cohesion, if it performs a set of tasks that relate to each other very loosely.Content coupling exists between two modules, if they share code.Д¬lassification of Cohesion Coincidental cohesion.This violets information hiding вЂ“ a basic design concept.Content coupling occurs when one component secretly modifies data that is internal to another component.

Common coupling can leads to uncontrolled error propagation and unforeseen side effects when changes are made.Two modules are common coupled, if they share data through some global data items.An example of control coupling is a flag set in one module and tested in another module.If data from one module is used to direct the order of instructions execution in another.This occurs when Class B is declared as a type for an argument of an operation of ClassA.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 is a special case (or extension) of data coupling.An example is an elementary (primal) data item passed as a parameter between two modules, e.g.Two modules are data coupled, if they communicate through a parameter.Stated simply, a cohesive module should (ideally) do just one thing. A cohesive module performs a single task, requiring little interaction with other components. Cohesion is an indication of the relative functional strength of a module.

Difference between coupling and cohesion in software engineering ppt