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> Examples of Trees

Examples of Trees

Even if the concept of tree structures isn't familiar to you, you are bound to be familiar with many examples. Any printed material that is divided into sections and subsections is organized as a tree; textbooks and legal documents are particularly notable. Large companies are organized as trees, with a president at the top, a vice-president for each division, and so on; similarly for governments. Mailing addresses, too, are trees—instead of sending mail to, say, house #187598003, we send it first to the correct country, then to the correct state, and similarly to the correct city, street, and house number. (I'm ignoring the ZIP code because it overlaps with the city and state in a peculiar way.)

There are abundant examples of trees on computers, as well. File systems are the canonical example, I suppose: each drive is the root of an independent tree of files and directories (folders). File systems also provide a good example of the fact that any node in a tree can be identified by giving a path from the root. For example, here's the path to a random file from my browser cache.

C:\Program Files\Netscape\Users\Default\Cache\M0kvb40t.jpg

Web addresses—that is, HTTP URLs—seem like another good example, but really they're not, because they're not another example at all, they are essentially just a way of getting at part of a file system. To be fair, URLs do contain domain names (e.g., www.cs.cmu.edu), and domain names do form a beautiful and well-designed tree structure, but in practice I think the tree is too wide and shallow to be cited as a good example of hierarchical structure.


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@ May (2000)