Information retrieval, commonly referred to as IR, is the process by which a collection of information is represented, stored, and searched in order to extract items that match the specific parameters of a user's request—or query—for information. Though information retrieval can be a manual process, as in using an index to find certain information within a book, the term is usually applied when the collection of information is in electronic form, and the process of matching query and document is carried out by computer. The collection usually consists of text documents (either bibliographic information such as title, citation and abstract, or the complete text of documents such as journal articles, magazines, newspapers, or encyclopedias). Collections of multimedia documents such as images, videoclips, music, and sound are also becoming common, and information retrieval methods are being developed to search these types of collections...