Software architecture and design (VI) -- hierarchy

Hierarchy body

Hierarchy regards the whole system as a hierarchy , The software system is decomposed into logical modules or subsystems at different levels in the hierarchy . This method is usually used to design system software , Such as network protocol and operating system .

In the system software hierarchy design , The lower subsystem provides services to its adjacent upper subsystem , Thus calling lower level methods . The lower layer provides more specific functions , for example I / O service , Business , Dispatch , Security services, etc . The middle tier provides more domain related functions , Such as business logic and core processing services . and , The upper layer provides services such as GUI,shell More abstract functions in the form of user interfaces such as programming facilities .

It is also used to organize class libraries , Such as... In the namespace hierarchy .NET Class library . All design types can implement this hierarchy , And often combined with other architectural styles .

The layered architectural style is divided into -

• Main subprogram
• Master-slave
• virtual machine

Main subprogram

The purpose of this style is to reuse modules and freely develop a single module or subroutine . In this style , The software system is divided into subprograms by using top-down refinement according to the required functions of the system .

These refinements are vertically leading , Until the decomposed module is simple enough to bear exclusive responsibility . Functions can be reused and shared by multiple callers at the upper level .

There are two ways to pass data to subroutines as parameters , namely -

• Pass value - Subroutines use only past data , But it can't be modified .

• By reference ＆minu; Use subroutines and change the value of data referenced by parameters .

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