Software design principles : The principle of software design is very helpful to improve the quality of software design .

◆ abstract

Abstraction is the neglect of aspects of a subject that are not relevant to the current goal , In order to pay more attention to the aspects related to the current goal . Process abstraction and data abstraction are two main methods of abstraction .

◆ modularization

Modularity refers to the decomposition of a software to be developed into several small and simple parts —— modular , Each module can be developed independently , test , Finally, it is assembled into complete software . It's a complex problem “ divide and rule ” Principle of .

Modules are data structures and program codes that perform a specific task . A module has its external and internal characteristics .

◆ Information concealment

Information concealment is the rule used in developing the overall program structure , To conceal or encapsulate the components of each program in a single design module
, Define each module with as little internal processing as possible . The principle of information concealment to improve the modifiability of software , Testability and portability play an important role .

◆ Module independent

Module independence means that each module completes a relatively independent sub function , And the connection with other modules is simple . There are two measures to measure module independence : Coupling and Cohesion .

Coupling refers to the closeness of connection between modules . The higher the coupling degree, the worse the independence of the module .

According to the coupling degree from low to high, there are 7 Coupling mode .

         Indirect coupling ( Independent operation )

         Data coupling ( Transfer simple data with parameter table )

         Tag coupling ( Transfer a data structure or part of it )

         Control coupling ( The information transmitted includes the information of the control module )

         External coupling ( Modules are related to environments other than software )

         Public coupling ( Multiple modules refer to the same global data area )

         Content coupling ( Access internal data , Code overlap or multiple entries )

Cohesion refers to the closeness of the relationship among the elements within the module , The lower the cohesion, the poorer the independence of the module .

According to the degree of cohesion, there are 7 Species cohesive species .

         coincidental cohesion ( Multiple tasks completed by the module , Loose relationship between tasks )

         Logical cohesion ( Module completes a set of logically related tasks )

         Instantaneous cohesion ( All tasks of the module must be performed at the same time interval )

         Procedural Cohesion ( The processing elements of the module are related and executed in a specific order )

         Communication Cohesion ( All elements of the module are concentrated on one data structure area )

         Sequential Cohesion ( Module processing element correlation , Must be executed in sequence )

         Functional Cohesion ( Module accomplishes a single function , Coordination of all parts , And indispensable )

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