The growth of the Internet and the availability of enormous volumes of data in digital form has necessitated intense interest in techniques for assisting the user in locating data of interest. The Internet has over 350 million pages of data and is expected to reach over one billion pages by the year 2000. Buried on the Internet are both valuable nuggets for answering questions as well as large quantities of information the average person does not care about. The Digital Library effort is also progressing, with the goal of migrating from the traditional book environment to a digital library environment. Information Retrieval Systems: Theory and Implementation provides a theoretical and practical explanation of the latest advancements in information retrieval and their application to existing systems. It takes a system approach, discussing all aspects of an Information Retrieval System. The importance of the Internet and its associated hypertext-linked structure is put into perspective as a new type of information retrieval data structure. The total system approach also includes discussion of the human interface and the importance of information visualization for identification of relevant information. The theoretical metrics used to describe information systems are expanded to discuss their practical application in the uncontrolled environment of real world systems. Information Retrieval Systems: Theory and Implementation is suitable as a textbook for a graduate-level course on information retrieval, and as a reference for researchers and practitioners in industry.