Library The library is a place where books, journals, microfilms, audio and visual materials are kept and organized to support the cultural, informational, recreational, and educational needs of the general public or specific groups of users. Recent advances in computing and communication technologies have transformed the contemporary library: it is not only a warehouse, but now also an active member in a vast network of libraries and databanks through which users have access to a world-wide store of recorded knowledge. The most common kinds of libraries are public libraries and those of schools, colleges and universities, and government. In addition, many specialized libraries serving industry, commerce, the media, and the professions have been established during the past half century. In the United States and Canada alone more than 135,000 libraries exist, ranging in size from the Library of Congress to the smallest elementary school facilities. Classification Systems and the Catalog Library classification systems permit users to find a particular book or author, or to discover what books on a particular subject are held by the library. Most libraries use one of three major classification systems: the Dewey Decimal System, invented by Melvil Dewey the Universal Decimal Classification, a European adaptation of Dewey or a system developed by the Library of Congress. The library's catalog not only lists the library's contents but also analyzes them, so that all works by an individual author, all works on a given subject, and all works in a specific category (dictionaries, music, or maps, for example) can be easily located by readers. The modem catalog is a practical tool that is the result of the analysis of the subject, category, and contents of books, videocassettes, microfilms, compact discs, and a host of other informational vehicles. The library's own card catalog is only one of the many forms in which catalog and bibliographic materials are available. Large libraries own the National Union Catalog, for example, a cumulative listing of the library resources of the Library of Congress and other major and specialized libraries in the United States and Canada. Specialized libraries may own or subscribe to such specialized catalogs as the Eighteenth Century Short Title Catalog (ESTC), a computerized database listing every publication--book, pamphlet, or single sheet -- printed between 170l and 1800 in English or, if in a foreign language, in English-speaking countries. Cataloging and classifying are expensive processes. Many libraries cut expenses by subscribing to a computerized bibliographic service. To locate materials that are not among its. holdings, a library may inquire the Online Computer Library Center ( OCLC ) or the Research Libraries Information Network (RLIN), which are the two major national catalog networks. Through their computerized databases, these networks offer interlibrary loan services that can operate, if necessary, across the continent. History The earliest ancient libraries were clay tablet storerooms in ancient Mesopotamia, and the later papyrus scroll libraries in Egypt, Greece, and Rome. Ashurbanipal's library in Nineveh (7th century BC) consisted of thousands of inscribed clay tablets recording laws, astronomical data, commercial transactions, narrative poems, and royal happenings. A 30,000-tablet library has been discovered at diggings in the ancient Sumerian city of Nippur, and other extensive libraries have been found throughout the Mesopotamian region. The earliest large Greek library is traced to Aristotle (4th century BC), but the greatest was established (3d century BC) by Ptolemy I in the museum at Alexandria, Egypt. Scholars there copied, revised and edited works of the classical Greek writers. Their copies of ancient works became the standard editions on which other