Page 224 - Building Digital Libraries

Thinking about Discovery

current-generation digital repositories for bibliographic description. These
chapters discussed the various ways that XML-centric metadata systems
are changing the way that systems and individuals can interact with their
descriptive data, and the chapters discuss the major technologies currently
being utilized in conjunction with these XML-centric descriptive systems.
Likewise, the library community has come to rely on a specific set of com-
munication protocols to allow the remote searching of local systems.
Since the late 1990s, the library community has seen an explosion in
the number of communication protocols being utilized for library services.
Protocols like LDAP for authentication, OAI for data harvesting, and
OpenURL and DOI for linking are playing a key role in how the library of
the twenty-first century interacts with its users. And what’s more, for the
first time, the library community isn’t just looking within its own commu-
nity, but is looking outside of that community for communication and data
transfer protocols that are easy to implement and can provide a robust level
of search and integration. Digital repository administrators need to care-
fully consider both what communication protocols they wish to support,
and at what level they want to support real-time federated searches of their
content. Given the array of protocols available, this analysis will focus on
the three search protocols that enjoy the widest support within the library
community and beyond: Z39.50, SRU/W, and OpenSearch. While other
protocols exist, these three protocols are nearly universally supported by
federated search systems and provide a great deal of flexibility in terms of
query support and metadata formats.

Z39.50
Z39.50 is the grandfather of federated searching within the library commu-
nity. The protocol traces its roots back to the early 1970s as a way for large
bibliographic databases like the Library of Congress and OCLC to share
bibliographic data between systems. In 1979, a National Information Stan-
dards Organization committee was formed to investigate the development
of a standard data protocol that could facilitate bibliographic data-sharing.
These efforts culminated in the development of Z39.50–1988, or Z39.50
Version 1. As documented later by Clifford Lynch, Version 1 was basically
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a theoretical concept draft that was virtually unimplementable. In retrospect
Lynch, one of the original members of the Z39.50 committee, would call the
first Z39.50 draft an utter fiasco that should never have been approved by the
committee. Following the approval of Version 1, the Library of Congress
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was appointed as the maintenance agency for the protocol.
The protocol was subsequently revised again in 1992 (Z39.50–1992),
expanding the protocol’s capabilities and borrowing heavily from work that
was internationally published as ISO 10162/10163. However, like the previ-
ous version of the protocol, Z39.50 was still tied to the OSI framework. The
OSI (Open Systems Interconnection) model is a seven-layered conceptual

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