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Types of cohesion

It is important to know that cohesion is a qualitative measure. It cannot be measured in units. Rather, it is expressed as being “High” or “Low” when discussing it. There are certain types of cohesion. They are explained below in an ascending order of degree (low to high): 1. Coincidental Cohesion -‘Coincidently’ means ‘by chance’. This, coincidental cohesion is a situation in which the modules of a program are divided into sub-parts (say, after every nth line). -This is said to be the worst type of cohesion and occurs when the concepts of modular programming and cohesion are not clear to the programmer. 2.Logical Cohesion - When modules of a program are grouped together due to a small relationship between them, it is called Logical cohesion. - This can be seen when two or more modules are having some code in common. When this type of cohesion is encountered, it is important to split such a logically cohesive module into smaller parts. 3.Temporal Cohesion - Sometimes, it so happens that certain procedures or functions are performed at the same time are grouped and put inside a single module. - When this happens, all the procedures that are to be executed simultaneously are found in a single module. - An example is that of the opening of a file in a program and the exception handler that tells the user if the opening of the file was unsuccessful. 4.Procedural Cohesion - Sometimes, related functions maybe put into the same module, say, when they are to be executed in a sequence that is repetitive. - This achieves what is called Procedural cohesion. 5.Communicational Cohesion -Communicational cohesion is when the parts of the same module act or work upon the same data. 6.Functional Cohesion - This is the highest degree of cohesion and so also the most desirable type of cohesion. - When a module is functionally cohesive, it signifies that all the parts of the module are put together into it because they perform as single, well-defined function or task. - Such a module is then called a perfect module. It is to be noted that it may not always be possible to have functional cohesion in a program or module