igher-levels show the interactions between the package specifications (to use the Ada terminology) and lower-levels of STC are used to define the package bodies.
             The relationships between modules are shown by calls. The existence and direction of the call indicates that a module has the means to call the other module and that, at "runtime"; the module may call the other module zero or more times. Typically, the STC contains a hierarchy of modules with calls used to show how one module will call another. As module calls normally involve the passage and return of parameters (or arguments), the STC depicts these with couples. Data and control couples are provided that indicate the passage or return of an item of data or some value that controls the operati
             ...