Introduction

With the rapid growth of the World Wide Web, the task of classifying natural language documents into a predefined set of semantic categories has become one of the key methods for organizing online information. This task is commonly referred to as text classification. It is a basic building block in a wide range of applications. For example, directories like Yahoo! categorize Web pages by topic, online newspapers customize themselves to a particular user’s reading preferences, and routing agents at service hotlines forward incoming email to the appropriate expert by content. While it was possible in the past to have human indexers do the category assignments manually, the exponential growth of the number of online documents and the increased pace with which information needs to be distributed has created the need for automatic document classification.