What is the maximum fan-in number for a system structure diagram?

The maximum fan-in number of the system structure diagram refers to the number of module lines in the system structure from the highest level to the lowest level that can be called; fan-in refers to the number of superior modules that directly call the module. A large fan-in indicates a high reusability of the module.

System structure diagram is a description method used in structured design methods, also called structure diagram or control structure diagram. It represents the hierarchical decomposition relationship of a system (or functional module), the calling relationship between modules, and the transfer relationship of data flow and control flow information between modules. It is the main diagram tool for describing the physical structure of the system.

The number of rows with the most modules is the maximum fan-out number. (Recommended Learning: PHPSTORM )

## The maximum fan income refers to the number of module rows with the lowest level that can be called from the superior to the lowest level.

Fan-in: refers to the number of superior modules that directly call this module. A large fan-in indicates a high reusability of the module.

The maximum number of fan-outs refers to the maximum number of subordinate modules that can be directly called by a module in the system structure.

Fan-out: refers to the number of subordinate modules directly called by this module. A large fan-out indicates that the module has high complexity and requires control and coordination of too many lower-level modules.

The concepts of fan-in and fan-out refer to the hierarchical calling situation between application modules. According to the structured design method, an application is composed of multiple modules with relatively independent functions.

Some concepts in module structured design:

Modularization: decompose a software to be developed into several small and simple parts - modules, each Each module can be independently developed, tested, and finally assembled into a complete program. This is a "divide and conquer" principle for complex problems. The purpose of modularization is to make the program structure clear, easy to read, easy to understand, easy to test, and easy to modify.

Module independence: Each module completes a relatively specific and independent sub-function, and has a simple connection with other modules. There are two measurement metrics: coupling between modules and cohesion of modules. Strong module independence must achieve high cohesion and low coupling.

Control level: Indicates the organization of program components (modules). The control hierarchy is often represented by the program's hierarchical structure (tree or network).

1. Depth: The number of levels of the program structure can reflect the scale and complexity of the program organization.

2. Width: the maximum number of modules in the same layer of modules

3. Module fan-out: the number of other modules called (or controlled) by one module

4. Module fan-in: the number of modules that call (or control) a given module

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