Welcome to a Z39.50 Instructional Site

This site is intended to be an introduction to the Z39.50 standard. Information for this site has been compiled from various sources.

The Problem

Z39.50 is the solution, so what's the problem. If you've ever tried to search on various databases -- electronic, library catalogs, etc. -- you've had to struggle with learning and using various interfaces to access each database. Z39.50 enables multiple diverse databases to be searched from the same interface. Also, if you don't know how data is indexed in the databases, your searching strategy can be affected. Z39.50 in combination with various profiles can assist with this difficulty as well.


What is Z39.50?

"Z39.50 is a computer-to-computer communications protocol designed to support searching and retrieval of information -- full text documents, bibliographic data, images, multimedia -- in a distributed network environment." (William E. Moen, 1995)

A Protocol

Designed to Support Searching and Retrieval

This protocol allows a patron to use a computer program ("a client") to submit an information request to multiple computer database servers without having to know how to search on each of the different databases. The client can then compile the results from the various servers and present them to the patron.

Models of How Z39.50 is Used in Information Retrieval

Z39.50 Model of Information Retrieval Z39.50 Model of Resource Discovery

Z39.50 acts as a translator between the "language" of the client and the "language" of the server.

Images used with permission of William E. Moen.

Difference between Client, Origin, Target, and Server

When discussing or reading about Z39.50, you need to know if you are talking about the client or the server. For example, if a vender tells you that you are purchasing Z39.50, does that mean that you are receiving a Z39.50 server or client or both?

What Z Is What Z Is Not
A computer-to-computer protocol A database language
A "language" for communication A search engine
A mechanism to search multiple databases at the same time Search commands
A mechanism to retrieve records and have them displayed as if they were on a local system A client interface

"The essential power of Z39.50 is that it allows diverse information resources to look and act the same to the individual user." (Sebastian Hammer and John Favaro)

What Can Z39.50 Do for Your Library

Z39.50 can help a library in many ways, but with the opportunities provided also come challenges. Some of these are listed below:

Opportunities Challenges
Enables a single interface for information retrieval -- choose a client carefully With sophistication comes complexity
Enables access to multiple, diverse databases, not just online library databases Z39.50 is misunderstood and is invisible to most users
Supports simple and sophisticated searching Unrealistic expectations
Allows flexible and customizable retrieval Differences in implementations -- see "Profiles" below

Benefits Drawbacks
Patrons will have easier access to information outside of the local library Costs -- check on grants
Access is given to multiple databases through one interface Complexity: for configuration, an understanding of both the library database and the server is needed
Access is given to multiple types of data through one interface Increased visibility and use
Can easily create a "union" catalog

How Does Z Do It?

How Does Z Accomplish Its Mission?

A Typical (Simple) Information Request

Required Services

Other Services

The Process of a Simple Query (from Z39.50's View)

Composition of a Query

REMEMBER: The patron has no knowledge of this composition. The patron enters information as requested by the client; the client composes the Z39.50 search query. The patron may only have to enter a name and click "Author Search."

Attribute Value Meaning
Use (1) 1003 Author
Relation (2) 3 Equal to
Structure (4) 1 Search term is a phrase
Truncation (5) 100 Do not truncate

Translation: 1=1003 2=3 4=1 5=100 "Twain, Mark"

If we change the search to an "Author-name Personal" and include right truncation, the query becomes:

Translation: 1=1004 2=3 4=1 5=1 "Twain, Mark"

Differences in Implementations

Since much of the Z39.50 standard allows for options, software vendors may implement the standard in somewhat different ways and still be "Z39.50 compliant." Also, differences in the way the database is created (indexed) can lead to results that are not consistent. Some examples of things to consider:

The Answer is "Profile"

Interoperability Testbed

Funded by a grant from the Institute of Museum and Library Services, the University of North Texas, School of Library and Information Sciences and Texas Center for Digital Knowledge are working to create an interoperability testbed. "The project, Realizing the Vision of Networked Access to Library Resources: An Applied Research and Demonstration Project to Establish and Operate a Z39.50 Interoperability Testbed, will design and demonstrate test methods and metrics to assess interoperability between systems using the ANSI/NISO Z39.50 standard protocol for information retrieval. The overall goal for the project is to improve Z39.50 semantic interoperability among libraries for information access and resource sharing." -- from the project web site


This site was compiled by Mike Pullin. Please send comments, suggestions, and corrections to mike@txmike.com.

Last updated: September 29, 2004.