Cassell, Kay Ann Reference and information service in the 21st century: An introduction - 2nd ed. - New York: Neal-Schuman Publishers, Inc., 2009 - xvii, 461p. ISBN: 978-1-55570-672-2 Subjects--Topical Terms: Information services Subjects--Index Terms: Reference Bibliographic resource Universal Decimal Class. No.: D 027.081 / P9