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The Z39.50 protocol

Z39.50 is commonly used to refer to the service and protocol defined by international standard ISO 23950: Information retrieval (Z39.50) – Application service definition and protocol specification and standard ANSI/NISO Z39.50.

The Z39.50 protocol was invented in the late 1980s and became an American NISO (National Information Standards Organization) standard recognized and adopted by ISO in March 1997 under the name ISO 23950.

Z39.50 is developed by ZIG (Z39‐50 Implementers Group) and managed by the “Z39‐50 Maintenance Agency” housed by the Library of Congress.

Protocol description

The Z39.50 standard defines a client-server relationship based on a service and a protocol for retrieving and transferring information.
This information may be in MARC structured exchange formats in accordance with standard ISO 2709: Information and documentation – Format for information exchange.

The Z39.50 protocol specifies procedures and formats enabling a client to query a database made available by a server, identify information corresponding to the search criteria, and retrieve the information thus identified.

Unlike a harvester, Z39.50 operates in synchronous mode. Queries received from the client are run directly on the remote server, and the results are sent back immediately.

Examples of use

  • Record retrieval: BnF and OCLC
  • Shared search engines:
    • portals
    • collective catalogs: CCFr and TEL (The European Library)

Different published versions of the standard

The American standard published in 1988 (version 1 Z39.50-1988) was first updated in 1992 (version 2: Z39.50-1992).
The implementation of these first two versions is identical.

A new version (version 3: Z39.50-1995), the implementation of which is compatible with versions 1 and 2, was published in 1995 and revised in 2003. This version contains clarifications, amendments, and corrections.

International standard ISO 23950 is based on versions 2 and 3, and presupposes that versions 1 and 2 are identical.

Thursday, March 21, 2013

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