Z39.50 is an international standard client–server, application layer communications protocol for searching and retrieving information from a database over a TCP/IP computer network, developed and maintained by the Library of Congress.
In practice, the functional complexity is limited by the uneven implementations by developers and commercial vendors.
Z39.50 is a pre-Web 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.
These projects have a much lower barrier to entry for developers than the original Z39.50 protocol,[2] allowing the relatively small market for library software to benefit from the web service tools developed for much larger markets.