In structure chart whole application is divided into modules (set of program instructions) and modules are designed according to some principles of design. These are:

Modularity and partitioning: Every system must comprises a hierarchy of modules. Lower level modules are usually smaller in size and scope compared to higher level modules. They serve to partition processes in separate functions.

Coupling: Modules must be loosely coupled. Which means that modules must have little dependence on other modules in a system.

Cohesion: Modules must be highly cohesive. It means that modules must carry out a single processing function.

Span of control: Modules must interact with and manage functions of a limited number of lower level modules. It means that number of called modules must be limited (in a calling module).

Size of Module: Number of instructions present in a module must be limited so that module size is normally small.

Shared use of Functions: Functions must not be duplicated in separate modules may be shared. It means that functions can be written in a single module and can be invoked by any other module when required.