If the software is to be developed in-house, it is at this point in the development process that we must specify the software design (i.e., detailed, internal design). The modular design of the software is one of the features unique to structured systems development. The main tool of the structured design process is the structure chart, a graphic tool for depicting the partitioning of a system into modules, the hierarchy and organization of these modules, and the communication interfaces between the modules. 1
The structure chart’s overall appearance is similar to that of an organization chart. Each box on a structure chart is a module. These structure chart modules become computer program modules of 30 to 60 lines of computer program code (one-half to one page of code). During structured systems design, related activities are grouped together within a module. This grouping of activities leads to a more maintainable system because changes to one function of a system lead to changes in a minimum of modules.