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CHAPTER 9

model that describes how information moves from the application level in
an environment, through the network level, and to the application level of
a target (see figure 9.4).
For practical purposes, the Z39.50–1992 draft was practically unimple-
mentable due to the draft’s continued reliance on the OSI framework—
particularly a desire to make use of the presentation layer within the OSI
model. This coupling hamstrung developers, and continued to be a barrier
for implementation. Recounting his work with the Z39.50 community,
Clifford Lynch notes:

By 1992, it was already clear to most implementers that OSI
had failed, but this was not yet a politically acceptable statement
within international standards bodies or certain US government
and library circles. There was at least one OSI-based implementa-
tion of Z39.50–1992, which was developed but never exercised
because there was nobody to talk to—and no way of talking to
FIGURE 9.4 anyone. To move Z39.50 from theory to practice it was necessary
OSI Model to move it into the TCP/IP based environment of the Internet,
despite the political controversy that this would entail. 8
Given OSI’s failure to gain traction, CNI initiated the development of Z39.50
over a TCP/IP connection, leading to the subsequent revision (Version 3)
in 1995. Z39.50–1995 (Version 3) expanded the available attribute set for
searching, and also provided guidelines for implementing Z39.50 over a
TCP/IP connection. These changes allowed Z39.50 to be utilized for the
9
first time in widespread deployment by software and content developers
alike within the library community. Z39.50–1995 was quickly adopted by
the major library ILS vendors and became the standard by which records
could be shared and contributed to remote library systems. Content provid-
ers would later provide support for Z39.50 as a means for building citation
applications and facilitating basic levels of remote searching in the content
repositories. Citation software like EndNote would later be developed as
a robust citation management application utilizing Z39.50 to query and
retrieve metadata about specific titles within a database.
So, what is Z39.50? Z39.50 is a stateful connection between a client (or
origin) and a server (target). Z39.50 supports two levels of search—what
are known as a SCAN and a SEARCH. SCAN requests retrieve result sets
containing minimal metadata—basically an item’s title. These requests pro-
vide a quick mechanism for retrieving a results list within a selected target.
Once an item has been selected, a request for the full item’s metadata can
be made on the server. The second type of request is SEARCH. A SEARCH
differs from a SCAN request in regard to the data being made available
within the results set. Unlike a SCAN request, which returns a list of item
titles, a SEARCH request returns the entire metadata record for each item
within the results set.
Given the nearly universal support for the Z39.50 protocol within the
library community, one would think that the protocol has been a stunning

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