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Access to remote catalogs does not need to be embedded in an existing library catalog system. Free-standing Z39.50 client software exist, as do gateways that provide access to remote catalogs through a WWW form which invokes the Z39.50 protocol. From LC's Z39.50 Gateway, you can pick from a list of academic libraries and search any one of them using a similar search form. Notice that the catalogs are implemented using different software packages, which indicates that the local interface at each institution is likely to be very different. However, through the Z39.50 Gateway "client" the presentation is similar, (although the options may be different, depending on the Z39.50 "server" at the other end).
The Library of Congress also runs a Z39.50 server. As of September 1996, this server provides access from other catalog systems to the Library's Books and Name Authority files. However, access to other files (such as Audiovisuals and Maps) will be supported soon. The Library uses the combination of the Z39.50 Gateway "client" and the Z39.50 "server" to provide a forms-based interface to the Library's catalog through the World Wide Web. Library of Congress catalogers and acquisition specialists can use a Z39.50 client from within MUMS to retrieve catalog records from other sources (such as the Research Libraries Group, and foreign resources mounted locally using SiteSearch software) to use as a basis for building full catalog records. See a diagram showing the various Z39.50 components and links at the Library.
The combination of a "stateless" Z39.50 gateway client and the Z39.50 server can be used to create a link from a web-page that queries LC's catalog and returns a specified display of the results of that query. See examples of such searches.
The Library of Congress has been heavily involved with the development of Z39.50 from its beginnings in the Linked Systems Project which involved LC, OCLC, and the Research Libraries Group. The Z39.50 Maintenance Agency is at LC. Most current implementations of Z39.50 support access to traditional library catalog records (with fields such as author, title, and subject), but the Z39.50 community has been developing profiles designed to provide the same type of interoperability for access to other types of resource, including collections of ASCII full-text (the WAIS profile) and records describing sources (such as databases or WWW sites) for government documents (the GILS profile). During the summer of 1996, the first attempt was made to develop a profile that might be appropriate for access to collections with the characteristics and complexities of the American Memory and Thomas collections. The hope is that eventually, the Library would be able to provide this type of access to its digital collections, but a production repository will probably have to be in place before the hope can be realized. For more information on the Z39.50 profiles under development, see the Z39.50 Maintenance Agency
Z39.50 is one of the important components for LC's plans for information retrieval over the next few years. See this diagram (designed by Jim Stephens and drawn by Virginia Vitucci of ITS) to see how Z39.50 can link different "clients" (with different user interfaces) to LC's information "servers." A similar, but more comprehensive diagram incorporates other clients and servers (including the repository in which NDLP collections are expected to be stored).
Z39.50 is a client-server protocol, which allows the user interface to be on one computer and the searched database on another. This type of distributed system has many advantages. For an easy-to-read discussion of why Z39.50 is important, Walt Crawford has an essay on "Distributed Power" in his The Online Catalog Book, pages 89-94. [G.K.Hall & Co., 1992, LCCN 92-13843]
Glossary -- A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
NDLP Documentation: Intro -- Index
NDLP Glossary - Z
Comments: (10/23/97)
