N-1-3-020.20.2, "A Progress Report on the Implementation of the Z39.50 Information Retrieval Protocol", by Clifford A. Lynch*, The Z39.50 information retrieval protocol became a US national standard in 1988; it was developed by the National Information Standards Organization (NISO), the ANSI-accredited standards writing body serving the library, information services and publishing communities. The 1988 version saw little implementation, though it was used (in modified form) as the basis for the current version of the Wide Area Information Server (WAIS) system. Since 1988, work has been underway which culminated in the completion of version 2 of the standard, which was adopted in early 1992 and will be published shortly. Version 2 of the standard makes use of ASN.1 as an encoding mechanism, adds considerable functionality, and fixes a number of problems with the original standard. There is also an international analog (ISO 10162 and 10163) which is a subset of Version 2 of the US standard; this has reached IS status. A number of interoperable implementations of Version 2 of Z39.50 are now operational on the internet, with more on the way. While the Z39.50 standard was done within the OSI framework, the vast majority of the current implementations run over TCP/IP; the approach is to layer the Z39.50 application layer directly on top of a TCP/IP connection using TCP port 210 to contact the server. Currently running servers include bibliographic databases at the University of California (the MELVYL system at the office of the president and a campus-wide information server at UC Berkeley), Pennsylvania State University (the LIAS catalog), OCLC, the Research Libraries Information Network, and AT&T Bell Labs library. A number of these organizations also have running clients, as well as Dartmouth University and several library automation vendors, including Data Research Associates, NOTIS, Gaylord, and Innovative Interfaces. A number of other implementations are expected to be on the net within the next few months; it is hoped that these will include a new version of WAIS upgraded to support Z39.50 Version 2. A working group called the Z39.50 Interoperability Testbed operating under the auspices of the Coalition for Networked Information is seeking both to further interoperability among the developing implementations and to extend implementations to support additional nonbibliographic classes of information, such as fulltext documents and images. There is an active implementor's group which maintains a LISTSERV called Z3950IW at NERVM.BITNET; this group is meeting quarterly to move forward on the development of Version 3 of the standard, which will add a great deal of additional functionality. It is hoped that Version 3 will be ready for ballot sometime in 1993. One of the extensions targeted for version 3 is a facility called EXPLAIN, which permits a server to describe itself and its contents to clients and eliminates much of the current need for outside of protocol agreements between clients and servers in order to achieve interoperation. Z39.50 is viewed as a basic building block for the development of networked information servers; it provides a common search syntax and protocol control structure allowing clients to search information resources on the network and retrieve results from these servers without regard to the specific database structures in which information is stored. *Director, Library Automation University of California Office of the President