OCLC has a database, WorldCat, for cataloging and searching purposes which is used by librarians and the public. Contributions to WorldCat are made via a computer program, Connexion, which was introduced in 2001; the Connexion predecessor, OCLC Passport, was phased out in May 2005.
WorldCat contains records in MAchine Readable Cataloging ("MARC) format contributed by library catalogers worldwide who use OCLC as a cataloging tool. These MARC format records are then downloaded into the libraries' local catalog systems. This allows libraries to find and download records for materials to add to their local catalog without the lengthy process of cataloging each individually.
As of March 2015, the OCLC database contained over 336M records with 2.2 billion cataloged items, and is the world's largest bibliographic database covering 72,000 libraries. Connexion is available to professional librarians as a computer program or on the web at connexion.oclc.org.
WorldCat is available to the public for searching via a subscription web-based service called FirstSearch, as well as through the publicly available WorldCat.org.
OCLC assigns a unique control number (referred to as an "OCN" for "OCLC Control Number") to each new bibliographic record in the WorldCat. Numbers are assigned serially, and as of mid-2013 over a billion OCNs had been created. In September 2013, the OCLC declared these numbers to be in the "public domain, removing a perceived barrier to widespread use of OCNs outside of OCLC itself. The control numbers link WorldCat's records to local library system records by providing a common reference key for a record across libraries.
OCNs are particularly useful as "identifiers for books and other bibliographic materials that do not have "ISBNs (e.g., books published before 1970). OCNs are used as identifiers often in "Wikipedia and "Wikidata. In October 2013, it was reported that out of 29,673 instances of "Infobox Book in Wikipedia, "there were 23,304 ISBNs and 15,226 OCNs"; and regarding Wikidata: "of around 14 million Wikidata items, 28,741 were books. 5403 Wikidata items have an ISBN associated with them, and 12,262 have OCNs."
OCLC also runs the "Virtual International Authority File (VIAF), an international name authority file. VIAF numbers are broadly used as standard idenfitiers.
OCLC acquired "NetLibrary, a provider of electronic books and textbooks in 2002 and sold it in 2010 to "EBSCO Industries. OCLC owns 100% of the shares of "OCLC PICA, a "library automation systems and services company which has its headquarters in "Leiden in the Netherlands and which was renamed "OCLC" at the end of 2007. In June 2006, the "Research Libraries Group (RLG) was merged into OCLC. On January 11, 2008, OCLC announced that it had purchased "EZproxy. It has also acquired "OAIster. The process started in January 2009 and from 31 October 2009, OAIster records are freely available via WorldCat.org. In January 2015, OCLC acquired Sustainable Collection Services (SCS). SCS offered consulting services based on analyzing library print collection data to help libraries manage and share materials. Other mergers and acquisitions are listed on the OCLC website.
OCLC has been criticized for "monopolistic practices. In July 2010, the company was sued by SkyRiver, a rival startup, in an "antitrust suit. Library automation company "Innovative Interfaces joined SkyRiver in the suit. The suit was dropped in March 2013, however, following the acquisition of SkyRiver by Innovative Interfaces.
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