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Report to the DLF on the Z39.50 Implementers' Group

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 simplify development.
  • 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 server.
  • 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 itself.

In the context of this discussion, significant questions arose:

  • 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 recommendations.

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.

  1. Revision and Reaffirmation of the Standard for NISO 5-Year Review

    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 standard?

  2. 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.

  3. 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.
  4. Separate the Z39.50 Protocol from its Use of BER as a Wire Protocol

    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.

  5. Simplify the Protocol Specifications to Focus on Core Features

    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 Language.

  6. 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 of requirements:

  • 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 protocols.
  • 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?

Moving Forward

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 decision?

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? JISC? Others?

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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