Z39.50
Encyclopedia
Z39.50 is a client–server protocol
for searching and retrieving information from remote computer
database
s. It is covered by ANSI
/NISO
standard Z39.50, and ISO standard 23950. The standard's maintenance agency is the Library of Congress
.
Z39.50 is widely used in library
environments and is often incorporated into integrated library system
s and personal bibliographic reference software
. Interlibrary catalogue searches for interlibrary loan
are often implemented with Z39.50 queries.
Work on the Z39.50 protocol began in the 1970s, and led to successive versions in 1988, 1992, 1995 and 2003. The Contextual Query Language (formerly called the Common Query Language) is based on Z39.50 semantics.
In practice, however, the functional complexity is limited by the uneven implementations by developers and commercial vendors. The syntax of Z39.50 is abstracted from the underlying database structure; for example, if the client specifies an author search (Use attribute 1003), it is up to the server to determine how to map that search to the indexes it has at hand. This allows Z39.50 queries to be formulated without having to know anything about the target database; but it also means that results for the same query can vary widely among different servers. One server may have an author index; another may use its index of personal names, whether they are authors or not; another may have no name index and fall back on its keyword index; and another may have no suitable index and return an error.
An attempt to remedy this situation is the Bath Profile
(named after Bath, England, where the working group
first met in 1999). This document rigidly specifies the exact search syntax to employ for common bibliographic searches, and the expected behavior of Bath-compliant servers in response to these searches. Implementation of the Bath Profile has been slow but is gradually improving the Z39.50 landscape. The Bath Profile is maintained by Library and Archives Canada
.
technology, and various working groups are attempting to update it to fit better into the modern environment. These attempts fall under the designation ZING (Z39.50 International: Next Generation), and pursue various strategies.
The most important are the twin protocols SRU
/SRW, which drop the Z39.50 communications protocol (replacing it with HTTP) but attempt to preserve the benefits of the query syntax. SRU is REST
based and enables queries to be expressed in URL
query strings; SRW uses SOAP. Both expect search results to be returned as XML
.
These projects have a much lower barrier to entry for developers than the original Z39.50 protocol, allowing the relatively small market for library software to benefit from the web service
tools developed for much larger markets.
Software:
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
for searching and retrieving information from remote computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
s. It is covered by ANSI
American National Standards Institute
The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...
/NISO
Niso
Niso is a genus of very small parasitic sea snails, marine gastropod mollusks or micromollusks in the family Eulimidae. -Species:According to the World Register of Marine Species the following species with accepted names are included within the genus Niso * Niso aeglees Bush, 1885* Niso albida...
standard Z39.50, and ISO standard 23950. The standard's maintenance agency is the Library of Congress
Library of Congress
The Library of Congress is the research library of the United States Congress, de facto national library of the United States, and the oldest federal cultural institution in the United States. Located in three buildings in Washington, D.C., it is the largest library in the world by shelf space and...
.
Z39.50 is widely used in library
Library
In a traditional sense, a library is a large collection of books, and can refer to the place in which the collection is housed. Today, the term can refer to any collection, including digital sources, resources, and services...
environments and is often incorporated into integrated library system
Integrated library system
An integrated library system , also known as a library management system ,is an enterprise resource planning system for a library, used to track items owned, orders made, bills paid, and patrons who have borrowed....
s and personal bibliographic reference software
Reference management software
Reference management software, citation management software or personal bibliographic management software is software for scholars and authors to use for recording and utilising bibliographic citations . Once a citation has been recorded, it can be used time and again in generating bibliographies,...
. Interlibrary catalogue searches for interlibrary loan
Interlibrary loan
Interlibrary loan is a service whereby a user of one library can borrow books or receive photocopies of documents that are owned by another library...
are often implemented with Z39.50 queries.
Work on the Z39.50 protocol began in the 1970s, and led to successive versions in 1988, 1992, 1995 and 2003. The Contextual Query Language (formerly called the Common Query Language) is based on Z39.50 semantics.
Search syntax
It supports a number of actions, including search, retrieval, sort, and browse. Searches are expressed using attributes, typically from the bib-1 attribute set, which defines six attributes to be used in searches of information on the server computer: use, relation, position, structure, truncation, completeness. The syntax of the Z39.50 protocol allows for very complex queries.In practice, however, the functional complexity is limited by the uneven implementations by developers and commercial vendors. The syntax of Z39.50 is abstracted from the underlying database structure; for example, if the client specifies an author search (Use attribute 1003), it is up to the server to determine how to map that search to the indexes it has at hand. This allows Z39.50 queries to be formulated without having to know anything about the target database; but it also means that results for the same query can vary widely among different servers. One server may have an author index; another may use its index of personal names, whether they are authors or not; another may have no name index and fall back on its keyword index; and another may have no suitable index and return an error.
An attempt to remedy this situation is the Bath Profile
Bath Profile
The Bath Profile is an international Z39.50 Specification for Library Applications and Resource DiscoveryThe syntax of Z39.50 is abstracted from the underlying database structure; for example, if the client specifies an author search , it is up to the server to determine how to map that search to...
(named after Bath, England, where the working group
Working group
A working group is an interdisciplinary collaboration of researchers working on new research activities that would be difficult to develop under traditional funding mechanisms . The lifespan of the WG can last anywhere between a few months and several years...
first met in 1999). This document rigidly specifies the exact search syntax to employ for common bibliographic searches, and the expected behavior of Bath-compliant servers in response to these searches. Implementation of the Bath Profile has been slow but is gradually improving the Z39.50 landscape. The Bath Profile is maintained by Library and Archives Canada
Library and Archives Canada
Library and Archives Canada is a national memory institution dedicated to providing the best possible account of Canadian life through acquiring, preserving and making Canada's documentary heritage accessible for use in the 21st century and beyond...
.
Modernization efforts
Z39.50 is a pre-WebWorld Wide Web
The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...
technology, and various working groups are attempting to update it to fit better into the modern environment. These attempts fall under the designation ZING (Z39.50 International: Next Generation), and pursue various strategies.
The most important are the twin protocols SRU
Search/Retrieve via URL
Search/Retrieve via URL is a standard search protocol for Internet search queries, utilizing Contextual Query Language , a standard query syntax for representing queries.-External links:* at Library of Congress...
/SRW, which drop the Z39.50 communications protocol (replacing it with HTTP) but attempt to preserve the benefits of the query syntax. SRU is REST
Representational State Transfer
Representational state transfer is a style of software architecture for distributed hypermedia systems such as the World Wide Web. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation...
based and enables queries to be expressed in URL
Uniform Resource Locator
In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....
query strings; SRW uses SOAP. Both expect search results to be returned as XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
.
These projects have a much lower barrier to entry for developers than the original Z39.50 protocol, allowing the relatively small market for library software to benefit from the web service
Web service
A Web service is a method of communication between two electronic devices over the web.The W3C defines a "Web service" as "a software system designed to support interoperable machine-to-machine interaction over a network". It has an interface described in a machine-processable format...
tools developed for much larger markets.
External links
- Z39.50 Maintenance Agency
- Z39.50 Standard Document (pdf)
- Bath Profile
- SRU Maintenance Agency
- Z-Brary Registry of z39.50 Targets
- IRSpy Z39.50 Target Directory
Software: