Page 226 - Building Digital Libraries

Thinking about Discovery

success—but this is not necessarily the case. While Z39.50 is widely sup-
ported within the library community, the protocol itself has failed to real-
ize its full potential. Even in the absence of viable alternatives, Z39.50 has
remained more of a fringe protocol, supported primarily in response to the
perceived need within the library community for its support, rather than
the actual utilization of the protocol. In part, this is due to the complexity
of the protocol itself. In the not too distant past, adding Z39.50 support
required the development of a Z39.50 server, including components for
encoding and decoding/encoding ASN.1/BER messages between the host
and target. Given the obscure nature of the protocol (i.e., it is used primar-
ily by the library community), this process was often a major barrier to
implementation, since only a handful of individuals outside of the vendor
community knew how to create the necessary components to utilize the
protocol. What’s more, the protocol itself is expensive in terms of the system
resources that need to be deployed. And with that said, Z39.50 has enjoyed
a reawakening of sorts—though this time, outside of the library commu-
nity. Within the GIS (geographic information systems) community, the
Z39.50 protocol is being used to build shared information networks like the
Federal Geographic Data Committee (www.fgdc.gov) and to create small
organizational networks through GIS software solutions that use Z39.50 as
the networking protocol. 10
While issues relating to the relatively expensive nature of the Z39.50
protocol have not been significantly overcome, adding support for the pro-
tocol has no longer become the primary barrier to implementation. This is
thanks largely to the open-source library community and the development
of a number of toolkits designed specifically for the integration of Z39.50.
Much of the credit for the simplification of the Z39.50 protocol goes to the
ZOOM (Z39.50 Object-Oriented Model) initiative. Started in 2001, the
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ZOOM initiative defined a set of object-oriented APIs that has been adapted
and ported to a wide variety of development languages. Toolkits such as
YAZ (Yet Another Z39.50 component) have provided the open source
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community with professional tools for creating or interacting with a Z39.50
server. Code examples utilizing these components can be found in numer-
ous languages like PHP, Ruby, PERL, C#, and so on. Digital repository
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administrators looking to implement Z39.50 support in their repositories
now have a simple set of toolkits that can be plugged into their repository
software, allowing quick Z39.50 integration. Of course, nowadays one must
evaluate if Z39.50 support is still valuable to one’s user community, since
more Internet-friendly protocols have begun to emerge and find a footing
within the library community.

SRU/SRW

While Z39.50 has been and continues to be an important protocol within the
library and digital library communities, the protocol’s reliance on ASN.1/
BER encoding makes it incompatible with the various XML-based systems

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