1 Information Retrieval on the Web

Introduction How do we find information on the Web? Although information on the Web is distributed and decentralized, the WWW can be viewed as a single, virtual document collection. In that regard, the fundamental questions and approaches of traditional information retrieval (IR) research (e.g., term weighting, query expansion) are likely to be relevant in Web document retrieval. Findings from traditional IR research, however, may not always be applicable in a Web setting. The Web document collection–massive in size and diverse in content, format, purpose, and quality–challenges the validity of previous research findings that are based on relatively small and homogeneous test collections. Moreover, some traditional IR approaches, while applicable in theory, may be impossible or impractical to implement in a Web setting. For instance, the size, distribution, and dynamic nature of Web information make it extremely difficult to construct a complete and up-to-date data representation of the kind required for a model IR system. To further complicate matters, information seeking on the Web is diverse in character and unpredictable in nature. Web searchers come from all walks of life and are motivated by all kinds of information need. The wide range of experience, knowledge, motivation and purpose means that searchers can express diverse types of information need in a wide variety of ways with differing criteria for satisfying their needs. Conventional evaluation measures, such as precision and recall, may no longer be appropriate for Web IR, where a test collection