Using the Z39.50 Information Retrieval Protocol
RFC 1729

Document Type RFC - Informational (December 1994; No errata)
Author Clifford Lynch 
Last updated 2013-03-02
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Network Working Group                                           C. Lynch
Request for Comments: 1729                      University of California
Category: Informational                          Office of the President
                                                           December 1994

            Using the Z39.50 Information Retrieval Protocol
                      in the Internet Environment

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.


   This memo describes an approach to the implementation of the
   ANSI/NISO Z39.50-1992 Standard for Information Retrieval in the
   TCP/IP environment which is currently in wide use by the Z39.50
   implementor community.


   Z39.50 is a US national standard defining a protocol for computer-
   to-computer information retrieval that was first adopted in 1988 [1]
   and extensively revised in 1992 [2]. It was developed by the National
   Information Standards Organization (NISO), an ANSI-accredited
   standards development body that serves the publishing, library, and
   information services communities. The closely related international
   standard, ISO 10162 (service definition) [3] and 10163 (protocol)
   [4], colloquially known as Search and Retrieve or SR, reached full
   International Standard (IS) status in 1991. Work is ongoing within
   ISO Technical Committee 46 Working Group 4 Subgroup 4 to progress
   various extensions to SR through the international standards process.
   The international standard is essentially a compatible subset of the
   current US Z39.50-1992 standard. Z39.50 is an applications layer
   protocol within the OSI reference model, which assumes the presence
   of lower-level OSI services (in particular, the presentation layer
   [5]) and of the OSI Association Control Service Element (ACSE) [6]
   within the application layer.

   Many institutions implementing this protocol chose, for various
   reasons, to layer the protocol directly over TCP/IP rather than to
   implement it in an OSI environment or to use the existing techniques
   that provide full OSI services at and above the OSI Transport layer
   on top of TCP connections (as defined in RFC 1006 [7] and
   implemented, for example, in the ISO Development Environment

Lynch                                                           [Page 1]
RFC 1729      Using the Z39.50 in the Internet Environment December 1994

   software). These reasons included concerns about the size and
   complexity of OSI implementations, the lack of availability of mature
   OSI software for the full range of computing environments in use at
   these institutions, and the perception of relative instability of the
   architectural structures within the OSI applications layer (as
   opposed to specific application layer protocols such as Z39.50
   itself). Most importantly, some of these institutions were concerned
   that the complexity introduced by the OSI upper layers would outweigh
   the relatively meager return in functionality that they were likely
   to gain. Thus, for better or worse, the decision was taken to
   implement the Z39.50 protocol directly on top of TCP (with the
   understanding that this decision might be revisited at some point in
   the future).

   During 1991-1993, a group of implementing institutions agreed to
   participate in the Z39.50 Interoperability Testbed project (sometimes
   referred to by the acronym "ZIT") under the auspices of the Coalition
   for Networked Information (CNI). Their primary objective was to
   encourage the development of many interoperable Z39.50
   implementations running over TCP/IP on the Internet. By mid-1993, a
   number of independent Z39.50 implementations were operational and
   able to interoperate across the Internet.

   The Library of Congress, in its role as the Z39.50 Maintenance Agency
   for NISO, maintains a registry of the implementors [8], which
   includes members of the Z39.50 interoperability testbed.

   This document describes implementation decisions by current
   implementors of Z39.50 in the Internet environment. These have been
   proven within the ZIT project and are being used by most of the
   members of the Z39.50 Implementors' Group (ZIG), an informal group
   that meets quarterly to discuss implementation and interoperability
   issues and to develop extensions to the Z39.50 protocol targeted for
   inclusion in future versions of the standard. Intended as a guide for
   other implementors who seek to develop interoperable Z39.50
   implementations running over TCP/IP, this document focuses on issues
   related to TCP/IP, and it does not address other potential
   interoperability problems or agreements that have been reached among
   the implementors to address these problems. It does include a few
   notes about extensions to the existing Version 2 protocol that are
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