Z39.50-2001

**Maintenance Revision**

**Ray Denenberg**

**Library of Congress/**

**Z39.50 Maintenance Agency**

**January 2002**

**Introduction**

NISO Z39.50-2001 is proposed as a maintenance revision of Z39.50-1995.
This memorandum is intended as a cover letter to the draft ballot; its
primary purpose is to describe how this new version differs from
Z39.50-1995, and the reasons for these changes. If you're familiar with
Z39.50 and its historical development, please feel free to skip the
following historical background (skip to ACollaborative Work of The ZIG
and Maintenance Agency since 1995@).

**Historical Background**

Momentum to standardize an information retrieval protocol heightened in
the early \>80s with the Linked Systems Project. LSP implementation
began in \>82 and it became operational in \>85. Its primary application
was a nationwide database of name authority records; searching of
authority records was a subsidiary application. Two application
protocols, Record Transfer and Information Retrieval, were developed to
support these two applications, record exchange and search, specifically
to support *authority* record exchange and search, but with sufficient
generality to support the two functions regardless of record type.

In 1983 the LSP participants B LC, RLG, OCLC, and WLN B submitted both
protocols to ANSI/NISO for consideration as American National Standards.
Attempts to standardize Record Transfer were eventually abandoned
(eventually the Record Transfer protocol was replaced by FTP for LSP).
There was however considerable U.S. interest in standardizing an
information retrieval protocol, and the LSP Information Retrieval
protocol was assigned to the NISO committee on application protocols who
prepared it for ballot, in 1984. It was designated by NISO as
\"Z39.50\", as it is known today. (NISO was formerly named Z39, and
continues to use that designation for its standards.)

The 1984 ballot failed within NISO, primarily because it was not yet
sufficiently well-developed. There was significant further development
over the next three years; Z39.50 was re-balloted in 1987, this time
successfully, and it was approved by ANSI and published in 1988. Thus
the first published version was Z39.50-1988.

Independently, in 1984, a work item was approved in ISO for a \"Search
and Retrieve\" protocol, SR. There were several drafts of the SR
standard between 1984 and 1991 when it was finally approved. The two
standards, Z39.50-1988 and SR, shared considerable common functionality,
but they were not bit-compatible.

**The ZIG and Maintenance Agency**

In 1990 the *Z39.50 Implementors Group* (ZIG) was established, initially
to share Z39.50 implementation resources. Over the past 12 years the
ZIG=s role has evolved, and during much of that period its primary
activity has been to develop and recommend enhancements to the standard.

Also in 1990 a *Maintenance Agency* for Z39.50 was established, at the
Library of Congress. In late 1991 the Maintenance Agency put forth
version 2 for ballot; it was approved in 1992. Version 2, developed by
the Maintenance Agency in collaboration with the ZIG, replaced and
superseded the 1988 version.

There were two broad categories of change in version 2: changes
necessary for alignment with SR, and the addition of features deemed
necessary by implementors, to provide sufficient functionality so that
implementation would be economically justified. Thus Z39.50-1992 was not
identical to but was a compatible superset of SR.

**Development of Z39.50-1995 (Version 3)**

Many additional enhancements had been proposed by ZIG members for the
1992 version, beyond those that were actually adopted. Several features
not yet fully developed or which had not achieved consensus were
deferred. Their adoption would have caused significant delay, which was
unacceptable because the Maintenance Agency had been assigned as its top
priority to revise Z39.50-1988 to achieve bit-compatibility with SR, and
to do so quicky, for the credibility of both efforts. The ZIG agreed to
defer the proposed new features in return for a commitment from the
Maintenance Agency that their development would proceed immediately, and
that the resultant subsequent version would be a compatible superset of
the 1992 standard.

Thus began in late 1991 an intensive collaboration between the ZIG and
Maintenance Agency towards Development of (what eventually became)
Z39.50-1995. The ZIG met roughly four times per year during that period;
for each meeting the Maintenance Agency prepared a new iterative draft
(there were a total of ten or so). Each was carefully scrutinized by
implementors and discussed at length both over the ZIG listserv and at
the ZIG meetings. In April 1994, the ZIG recommended that the draft be
finalized. It was balloted successfully in 1995.

The 1992 version came to be known as *version 2*, and the 1995 version,
*version 3*. Z39.50-1992 replaced and superseded Z39.50-1988, which
became obsolete. Z39.50-1995 is a compatible superset of the 1992
version.

**Disposition of SR**

Z39.50-1992 had been a compatible superset of SR (it included features
not in SR such as resource control, access control, and proximity
searching). In addition, widening the gap between SR and Z39.50 were the
new features developed for Z39.50-1995 (e.g. Sort, Scan, Explain,
Segmentation, Concurrent Operations, and Extended Services).

Beginning in1992, ISO advanced several proposals intended to narrow or
eliminate that gap, by process of alignment by individual amendment. In
1994, however, ISO decided that that process was excessively burdensome,
and instead adopted (by fast-track ballot) the text of Z39.50 verbatim
as an ISO standard, ISO 2950-1998.

**Collaborative Work of The ZIG and Maintenance Agency since 1995**

The Library of Congress maintains a Web page
(http://lcweb.loc.gov/z3950/agency) for matters pertaining to the
maintenance, ongoing development, and implementation of Z39.50.
Available via this page are various categories of information, including
the text of Z39.50, definitions of registered objects, and register of
implementors. Of particular relevance pertaining to the 2001 revision
are: clarifications, commentaries, defect reports, amendments, and
implementor agreements. These latter categories of information represent
much of the collaborative work of the ZIG and Maintenance Agency since
publication of Z39.50-1995, and it is this work primarily that is
incorporated into the proposed revision.

**Purpose and Scope of Revision**

The historical background provided above describes the circumstances and
reasons for the revisions in 1992 and 1995. Those circumstances and
reasons do not apply to this (2001) revision.

There are two primary purposes for this 2001 revision. First, ANSI
standards undergo periodic review/re-affirmation, every five years of
so. Thus re-affirmation of Z39.50 is appropriate in the 2000-2002
timeframe.

The second objective is to integrate the above mentioned information
into the standard=s text. These clarifications, amendments, etc., have
been approved by the ZIG, but have not undergone formal approval beyond
that; they have never been approved by a standards body. Many of the ZIG
participants feel that for the credibility of the standard, the
Maintenance Agency, and the ZIG, this body of work needs formal
approval, and that these individual elements need to be integrated into
the standard=s text.

A re-affirmation is usually very limited in scope; references may be
updated, errors and defects corrected, etc. This revision therefore
constitutes more than a re-affirmation. On the other hand it does not
represent a new version (i.e. AVersion 4\"). So we refer to this as a
Amaintenance revision@.

**Revision in Perspective**

This effort to revise Z39.50 has caused some confusion, given the wide
discussion of various other aspects of Z39.50\'s future.

There has been ongoing discussion of a new protocol version, Aversion
4\", not compatible with version 3 (or with Z39.50-1995). Version 4
might incorporate new models and mechanics, include new functionality,
and attempt to address intersystem-search requirements for the next
decade or so. Discussion has included decoupling the mechanics (syntax
and underlying protocol) from the topological, data, and
semantics/service models, thus allowing the possibilities of rendering
the protocol for instance into XML rather than ASN.1.

In addition, in recent years there has been substantial interest among
implementors in evolving Z39.50 to a more mainstream protocol, lowering
the barriers to implementation while preserving the existing
intellectual capital of Z39.50. This interest has resulted in a new
initiative known as ZING (Z39.50‑International: Next Generation),
described at http://www.loc.gov/z3950/agency/zing/zing.html.

This revision, Z39.50-2001, is not related to either of these two
efforts, neither of which would be compatible with Z39.50-1995 (i.e.
version 3). Z39.50-2001 is a compatible superset of Z39.50-1995. The
three efforts:

-   version 4

-   ZING

-   2001 revision

can be seen as complementary, independent initiatives which collectively
address the near-to-mid-term future of Z39.50.

**Summary of Changes in Z39.50-2001**

The following web pages describe much of the changes that have been
integrated into the revision:

-   **Implementor agreements.** See:
    [http://lcweb.loc.gov/z3950/agency/agree/agree.html]{.underline}

-   **Amendments**. See
    [http://lcweb.loc.gov/z3950/agency/amend/amend.html]{.underline}
    including:

```{=html}
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```
-   Duplicate Detection Service: See
    [http://lcweb.loc.gov/z3950/agency/amend/am2.html]{.underline}, and

-   Encapsulation. See:
    [http://lcweb.loc.gov/z3950/agency/amend/am3.html]{.underline}

```{=html}
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```
-   **Defect reports**. See
    [http://lcweb.loc.gov/z3950/agency/defects/defects.html]{.underline}

-   **Commentaries**. See
    [http://lcweb.loc.gov/z3950/agency/wisdom/wisdom.html]{.underline}

-   **Clarifications**. See
    [http://lcweb.loc.gov/z3950/agency/clarify/clarify.html]{.underline}

-   **Version 3 Baseline Requirements**. See
    [http://lcweb.loc.gov/z3950/agency/v3base.html]{.underline}

-   **Z39.50 Attribute Architecture**. See
    [http://lcweb.loc.gov/z3950/agency/attrarch/attrarch.html]{.underline}

-   **Negotiation Model** (Model for Z39.50 Negotiation During
    Initialization). See
    [http://lcweb.loc.gov/z3950/agency/nego.html]{.underline}

**Miscellaneous changes**

> **OSI**.
>
> All references to OSI (Open System Interconnection) are purged.
> Purging began in the 1995 version, and is now complete. Thus such
> concepts as Application Contexts and Presentation Contexts are gone;
> Aorigin@ and Atarget@ are completely replaced by Aclient@ and
> Aserver@.
>
> **ASN.1**
>
> All of the ASN.1 has been consolidated into a single appendix. This
> includes APDU as well as object definitions.
>
> **State Tables**
>
> State tables have been removed, along with accompanying prose and
> supporting definitions.

**Appendices**

The following table summarizes changes in the appendices.

+-----------------+-----------------+-----------------------------------+
| **Appendix in   | **Corresponding | **Changes**                       |
| Z39.50-1995**   | Appendix in     |                                   |
|                 | Z39.50-2001**   |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 1: OID | Appendix 1      | No additional substantial         |
| (object         |                 | changes. See note 1.              |
| Identifiers)    |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 2: CTX | none            | removed entirely                  |
| (application    |                 |                                   |
| contexts)       |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 3:ATR  | Appendix 2      | Bib-1 removed. See note 2.        |
| (attributes)    |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 4: ERR | Appendix 3:     | -   bib-1 renamed Ageneral        |
| (diagnostics)   | DIAG (name      |     diagnostic set@.              |
|                 | change)         |                                   |
|                 |                 | -   Diag-1 removed.               |
|                 |                 |                                   |
|                 |                 | -   AGeneral Diagnostic           |
|                 |                 |     Container@ added.             |
|                 |                 |                                   |
|                 |                 | -   AReturning Diagnostics in an  |
|                 |                 |     Init Response@ added.         |
+-----------------+-----------------+-----------------------------------+
| Appendix 5: REC | Appendix 4.     | -   The list of syntaxes and      |
| (record         |                 |     their oids is removed.        |
| syntaxes)       |                 |                                   |
|                 |                 | -   OPAC and Summary removed.     |
+-----------------+-----------------+-----------------------------------+
| Appendix 6: RSC | Appendix 5      | Resource-1 removed. See note 3.   |
| (resource       |                 |                                   |
| reports         |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 7:ACC  | Appendix 6      | No additional substantial         |
| (access         |                 | changes. See note 1.              |
| control)        |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 8: EXT | Appendix 7      | No additional substantial         |
| (extended       |                 | changes. See note 1.              |
| services)       |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 9: USR | Appendix 8      | -   Old USR.2 (negotiation        |
| (user           |                 |     records) has been removed,    |
| information     |                 |     superceded by new appendix    |
| formats)        |                 |     14.                           |
|                 |                 |                                   |
|                 |                 | -   New section Ause of Init      |
|                 |                 |     Parameters for User           |
|                 |                 |     Information@                  |
|                 |                 |                                   |
|                 |                 | -   New section AGeneral User     |
|                 |                 |     Information format, User-1\". |
+-----------------+-----------------+-----------------------------------+
| Appendix 10:    | Appendix 9      | -   eSpec-2 replaces eSpec-1.     |
| ESP (especs)    |                 |                                   |
|                 |                 | -   eSpec-q added.                |
+-----------------+-----------------+-----------------------------------+
| Appendix 11:VAR | Appendix 10     | No additional substantial         |
| (variant sets)  |                 | changes. See note 1.              |
+-----------------+-----------------+-----------------------------------+
| Appendix 12:TAG | Appendix 11     | No additional substantial         |
| (tagSets &      |                 | changes. See note 1.              |
| schemas)        |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 13:ERS | Appendix 12     | Unchanged                         |
| (result set     |                 |                                   |
| model)          |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 14:RET | Appendix 13     | No additional substantial         |
| (retrieval)     |                 | changes. See note 1.              |
+-----------------+-----------------+-----------------------------------+
| Appendix 15:PRO | Appendix 16     | completely re-written             |
| (profiles)      |                 |                                   |
+-----------------+-----------------+-----------------------------------+
| Appendix 16     | None.           |                                   |
| (maintenance    |                 |                                   |
| agency)         |                 |                                   |
+-----------------+-----------------+-----------------------------------+
|                 | Appendix 14:    | New in Z39.50-2001                |
|                 | NEGO            |                                   |
|                 | (Negotiation    |                                   |
|                 | model)          |                                   |
+-----------------+-----------------+-----------------------------------+
|                 | Appendix 15:    | New in Z39.50-2001                |
|                 | NEGO2           |                                   |
|                 | (negotiation    |                                   |
|                 | records)        |                                   |
+-----------------+-----------------+-----------------------------------+
|                 | Appendix 17     | New in Z39.50-2001                |
|                 | (attribute      |                                   |
|                 | architecture)   |                                   |
+-----------------+-----------------+-----------------------------------+

Notes:

1.  ANo substantial changes@ above mean none other than (perhaps)
    changes made in accordance with changes listed above before the
    table (which themselves may be substantial).

2.  Bib-1 attributes are no longer maintained within the text of Z39.50.
    They will continue to be maintained on the web site.

3.  Originally there was resource‑1, which listed 16 categories of
    resources, with no provision of extensibility. Resource‑2 was added
    in 1995, inheriting the original 16 categories, with provision for
    extensibility. Thus Resource‑2 is a compatible superset of
    resource‑1. Thus resource‑1 is dropped resource‑2 retained (with a
    comment to the effect that a client might want to be prepared to
    recognize the resource‑1 object identifier.)