Report to the DLF on the Z39.50
Moving Towards the Future of Z39.50. Issues and Options Based
on ZIG Meeting Discussions December 6-7, 2000
Denise Troll and Bill Moen
February 8, 2001
This document summarizes key issues, technical and perceptual
problems, potential solutions and opportunities identified by
presenters and participants at the December 2000 Z39.50
Implementers Group (ZIG) meeting. The problems and their
solutions affect both Z39.50 implementers and those who are
outside of the Z39.50 community.
The context in which Z39.50 operates today is much different
from the context in which active Z39.50 implementation began in
the early 1990s. In particular the networked environment has
evolved in ways few could have imagined at the time of the 1992
Z39.50 Interoperability Testbed, which placed the protocol on the
radar of many developers in the library community. Today, Z39.50
is one protocol among many that implementers must address.
Unfortunately, and for a variety of reasons, Z39.50 is no longer
even on the radar of key networked information retrieval
application environments. While attempts to examine and explain
how this happened would be informative, the more important
challenge is figuring out how to harness two decades of
intellectual and financial investment in Z39.50 to help solve
current critical information retrieval problems. The problems and
options explored at the December ZIG meeting suggest that Z39.50
and the ZIG will change profoundly in the future.
Factors Motivating and Constraining Change
Pressure for change derives from technical concerns about the
current Z39.50 standard and perception problems related to both
the standard and the ZIG. Many of the technical and perceptual
issues revolve around the role or place of Z39.50 in the context
of the Web. The future of Z39.50 is definitely related to its
potential roles on the Web. The Web, with its many tools and
technologies, provides the application and application
development environment in which Z39.50 must be considered. To a
certain extent, Z39.50 and Web technologies have already been
integrated, for example, through the implementation of Web-Z
gateways, the use of XML as a record syntax, the incorporation of
Dublin Core attributes for searching, etc. But though these
actions are important, they do not address the perceived and
actual barriers to integrating Z39.50 and the Web. In fact, such
actions may highlight the awkward fit of the two, for example,
statelessness vs. statefulness issues in gateways or getting an
appropriate DTD/schema for an XML object.
Perceptions of Z39.50 vary, but some of the common words used
are: broken, heavy weight, difficult, complex, and old
technology. Participants at the December 2000 ZIG meeting
articulated the following problems:
- Z39.50 documentation is difficult to understand.
- Z39.50 is difficult to implement and lacks tools that could
- Different developers implement Z39.50 differently, which
leads to interoperability problems.
- Some of the functions of Z39.50 may be unnecessary today,
unnecessarily complicating the standard.
- Z39.50 ties the application protocol to the transfer protocol
(BER), which many developers do not accept.
- Z39.50 lacks APIs, which many developers want.
- Z39.50 is not Web friendly.
- Many developers today do not want to run anything but an http
- Some ZIG members are wedded to a single protocol and expect
all implementations to interoperate.
- The standard and the ZIG are misunderstood and
misrepresented, which creates communication problems or barriers
among developers and implementers of different protocols.
Although people can articulate actual or perceived
shortcomings in the protocol and change is inevitable, the large
installed base of Z39.50 applications will necessarily constrain
radical changes to the technology. The Web appears to be the
?disruptive technology? that is changing the way organizations do
business. Even if Z39.50 remains a niche protocol within the
library environment, its vitality may continue to wane. If the
ZIG does not rise to the challenge, Z39.50 may be the ?sustaining
technology? that leads to obsolescence.
Strengths of Z39.50
A number of people highlighted the strengths of Z39.50:
abstract access points, ability to represent complex searches,
ability to represent complex data, rich records with identifiable
elements, and complex semantics for other information retrieval
functions (like extended services and access control), and the
fact that Z39.50 is available now. A concise description of
Z39.50 strengths would be valuable to ensure that the good points
of the standard are not lost as Z39.50 evolves.
The ZIG as Barrier or Enabler
The question of what should be done with Z39.50 cannot be
divorced from who will do it. A more problematic question is who
will decide what should be done. The ZIG has existed for ten
years, officially serving as an advisory group to the
Z39.50/23950 Maintenance Agency. In its first 5 or 6 years, the
focus was on protocol development. From 1992-1996, a core group
emerged to do the primary work, which resulted in the 1995
standard. Since that time, the ZIG has struggled for focus and
ZIG meeting attendance has been much more varied. The
internationalization of the ZIG has been of major benefit, but
the scheduling of meetings in Europe and North America has
contributed to the more varied attendance.
Presenters at the December 2000 ZIG meeting pointed out that
the ZIG feels like a closed group. While there are interesting
developments and initiatives using Z39.50, often the principal
implementers of those activities do not attend the ZIG meetings.
In the past two years, the focus and structure of ZIG meetings
have changed, but lingering perceptions of the way the ZIG used
to be may be a barrier hindering the participation of broader
development and implementation communities. Focused activities
such as the Bath Profile, the Z Species initiative, and the GILS
effort may offer a better response to critical needs than the ZIG
In the context of this discussion, significant questions
- Who or what is the ZIG?
- Are the attendees at any one ZIG meeting the people who can
provide the mandate or make decisions about significant changes
in the standard? Probably not. Is the list of registered Z39.50
implementers the body that can make such decisions? If so, what
is the decision making process?
- Has the ZIG outlived its usefulness?
- If the ZIG has outlived its usefulness, what organization
will do the work?
One alternative to the ZIG is a formal standards process such
as NISO, with a standards committee charged with particular
responsibilities. The ZIG process of the early 1990s provided a
way to relatively rapid protocol development, but it may not be
rapid enough when compared with the speed at which a consortium
such as W3C produces working drafts and proposes
Attendees at the December 2000 ZIG meeting offered different
solutions to the problems. The next section of this document
summarizes the options explored at the meeting.
Options for Changes to the Protocol
A number of options for changing Z39.50 surfaced at the
December meeting. The options are categorized below. The
categories are not necessarily mutually exclusive and in some
cases, starting on one option might lead to another option (for
example, option 3 might lead to option 2). The problems must be
carefully articulated and the impacts and benefits of potential
solutions seriously evaluated before any option is chosen.
- Revision and Reaffirmation of the Standard for NISO 5-Year
If nothing else is done with Z39.5, NISO requires a
reaffirmation of its standards every five years. This is
currently underway. According to Ray Denenberg, the forthcoming
revisions will be primarily textual, for example, changing
wording in the standard to remove unnecessary language from OSI,
and removing or revising appendices. The basic protocol
specifications will not change substantively. This approach
essentially confirms that Z39.50 meets a critical set of
requirements. It implies that the requirements themselves need
not be questioned or explored.
A more substantial revision of the standard could be
envisioned to simplify the text by separating what is required
for basic compliance from the additional services and
functionality that Z39.50 offers. The challenge is to make the
text more accessible without losing technical precision. To what
extent can this be done and who would do it? Should a technical
writer be hired to assist the Maintenance Agency in revising the
- Rewrite the Protocol from the Ground Up
Several different approaches could be taken and the
implications are far reaching. The basic assumption is that all
existing Z39.50 implementations would be orphaned. The first step
would be to identify and define requirements. How does the
current networked information retrieval environment differ from
the information retrieval environment that motivated the
development of Z39.50? What functions are needed in a protocol
for networked information retrieval? What are the problems to be
solved by a networked information retrieval protocol?
Certainly, a blank slate approach is appealing because it
transcends the bounds of existing implementations and would
enable the use of all available and emerging Web technologies and
application development tools. But the impact on the installed
base of Z39.50 applications would be monumental.
- Rewrite the Protocol as an XML Protocol A somewhat less
radical solution would be to jettison ASN.1/BER and rewrite
Z39.50 as an XML protocol, separating the application protocol
from the wire protocol. This approach could integrate the XML
Query Language developments. Recasting ASN.1 in XML could spark
discussion of protocol functionality, which would probably lead
to option 2 above.
- Separate the Z39.50 Protocol from its Use of BER as a Wire
This approach was presented in several ZIG meetings.
Abandoning BER would likely lead to encoding (probably by XER)
the ASN.1 messages into a character protocol such as SOAP or XP.
This would safeguard the intellectual investment in the Z39.50
protocol solutions to information retrieval, yet would offer more
Web friendliness. The focus of this approach is to repackage
Z39.50 strengths to make to make the standard more acceptable to
broader development and implementation communities.
This approach could include some protocol simplification (for
example, the pruning or elimination of some services and
features), but its primary intent is to separate the ASN.1
protocol specification from the BER encoding. Any pruning would
be in response to identified applications and requirements.
- Simplify the Protocol Specifications to Focus on Core
This option focuses on identifying the core 50% of
functionality for information retrieval to simplify and
facilitate rapid implementation. The organizational memory and
collective wisdom of the ZIG and Z39.50 development would be used
to revise the protocol specifications to solve 50% of the
functional requirements in the current networked environment. The
questions of who would decide what constituted the core 50%
functionality and what criteria would be used to make the
decision were not addressed.
This approach resembles option 2, but it is not focused
automatically on technologies such as XML and the XML Query
- Z39.50 as a Protocol Template
This may be a separate option or an option subsumed by one or
more of the options listed above.
First Principles and Requirements
What are the first principles of design, implementation, etc.
that will guide decisions to change Z39.50 in the future? Rapid
development and simple implementation are essential, but the ZIG
(or whatever body accepts the challenge) must articulate and
agree on the principles. Consideration of first principles
necessarily entails examining and specifying at least three types
- Applications Requirements: What applications need or
could use a networked information retrieval protocol (e.g.,
virtual catalogs, virtual library services, digital library and
digital museums, etc.)? Identifying potential applications is
necessary to articulate the second category of requirements, but
it is likely that any applications using a networked information
retrieval protocol will be using a range of other protocols as
well. In general there is a need for Z39.50 to work with other
- Functional Requirements: What are the various
functional requirements that must be addressed for the
applications? Are there core and auxiliary functions, and can we
focus on the 50% functionality to move ahead quickly?
- Development Environment Requirements: What are the
development tools widely deployed that the protocol must use,
including but not limited to Web technologies, programming
languages, and API contexts?
The networked world will not wait for the ZIG to make
decisions or to create a "right way" protocol. How does the ZIG,
the Maintenance Agency, NISO, or whoever, indicate that a
strategic decision about Z39.50's future has been made? What is
the timeline for making such a decision? How will such a decision
be made? Who will make the decision? Finally, what is that
The ZIG must commit to a path that leads Z39.50 forward. That
path may require the ZIG to meet more frequently than previously
planned. Meetings must have a clear focus and identify clear
deliverables, including what work will be done, how it will be
done, who will do it, and when it will be completed. Perhaps the
ZIG is not the appropriate body to make these decisions. If that
is the case, what is the forum that can take such actions? A NISO
task force? Something under the auspices of CNI? A group jointly
sponsored by several North American and European organizations?
Can funding sources be identified for such activity? IMLS? NSF?
The goal is to solve the problems articulated above so that
Z39.50 continues to serve information retrieval without other
groups having to redo the intellectual work that the ZIG has done
well. To be successful, the ZIG and Z39.50 must interact with
other development and implementation communities and standards.
The scope of information retrieval issues and problems today is
so broad that no one group or standard can hope to address or
solve them all. ZIG members were encouraged to attend the OAI
open meeting to learn more about the Open Archives Initiative of
the Digital Library Federation and begin thinking about how a
Z39.50 gateway (by exposing its metadata) can be a harvestable
service for the OAI and how an OAI harvesting service can
contribute metadata to Z39.50.
The ZIG agreed that the standard documentation must be
significantly revised to clarify the utility of Z39.50 and
simplify implementation, but revising the document alone is
insufficient to address the technical problems. The standard
itself must be changed and better tools must be provided for
application developers if Z39.50 is to reappear on the radar of
key networked information retrieval application environments. The
ZIG agreed that the first step in addressing the technical
problems is to separate the application specification (the ASN.1
semantics) from the transfer syntax (BER encoding). Z39.50
implementers will begin experimenting with different approaches
to accomplish this using XER, XP, SOAP or RFC 822.
The questions of who decides what to change in the standard
based on what criteria will be revisited at the next ZIG meeting,
tentatively scheduled for October 2001.
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