2.1 What it is

We do top-down design all the time in real life. For example, when we write a paper in an English writing class, we first identify the major sections of the paper (like introduction, background, and summary). Then, we write the content for each section. Sometimes, we even need to outline each section with subsections first.

Maps are also perfect examples of top-down design. If you visit any mapping website, a map shows different types of details depending on the ``zoom'' level. A map for the globe, for example, is unlikely to identify streets. Instead, it probably identifies nations and national capitals. A map for a country, on the other hand, may include states (provinces), major cities and state capitals. We may also see major highways, but probably not intrastate roads. A regional map will identify smaller towns and cities, as well as intrastate roads. Even at this level, local streets cannot be displayed.

Most books are also organized in parts, and then chapters within a part. This is especially the case for college-level textbooks.

Documents are usually organized in an office or even at home. A file cabinet contains drawers, a drawer contains hanging folders, a hanging folder contains regular folders, and a regular folder contains stapled documents.

Essentially, the term ``top-down'' means a hierarchical structure of details. At the top level, very little detail is revealed. At the bottom level, very fine detail is displayed. Between the top and the bottom, however, are levels that display intermediate detail.

Can you find more real-life examples of top-down hierarchies? In the computer context, how files and folders are organized is also a prime example of a top-down hierarchy.