As web sites become an integral part of an organization's operations and external communications, it is increasingly becoming more important to understand, model, and utilize web site traffic and visitors' online behavior effectively. By examining web log files, it is possible to determine not only what, when, and by whom documents are being viewed, but log files can also provide information regarding server load, unsuccessful requests, and valuable marketing information.

In addition to knowing what you can learn from a log file, it is equally important to understand what you can't learn from a log file. In particular what types of data are not captured in log files, what types of data are inherently incomplete, and what types of incorrect inferences can be made from log files.