Refers to systems that are organized in the shape of a pyramid, with each row of objects linked to objects directly beneath it. Hierarchical systems pervade everyday life. The army, for example, which has generals at the top of the pyramid and privates at the bottom, is a hierarchical system. Similarly, the system for classifying plants and animals according to species, family, genus, and so on, is also hierarchical.
Hierarchical systems are as popular in computer systems as they are in other walks of life. The most obvious example of a hierarchical system in computers is a file system, in which directories have files and subdirectories beneath them. Such a file organization is, in fact, called a hierarchical file system .
In addition to file systems, many data structures for storing information are hierarchical in form. Menu-driven programs are also hierarchical, because they contain a root menu at the top of the pyramid and submenus below it.