Information retrieval, or "search" has become the central and primary mode for access to internet information. As more and more information becomes available the search technology required to access and retrieve that information becomes complex at the same time it becomes more commonplace. The computer science research field of information retrieval has become more widely known in recent years and has attracted researchers from other areas of computer and information science. Information Retrieval is primarily concerned with effective search in large collections of information ranging in size from small personal collections of information housed on a PC, to multi-terabyte repositories of information such as the National Science Digital Library, and indexes of the entire Web typified by Google and Yahoo.