[Search] [pdf|bibtex] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 rfc2288                                                 
Internet Draft                                Clifford Lynch
draft-ietf-urn-biblio-00.txt        University of California
22 March 1997                                Cecilia Preston
Expires in six months                        Preston & Lynch
                                              Ron Daniel Jr.
                              Los Alamos National Laboratory

          Using Existing Bibliographic Identifiers
                   Uniform Resource Names

Status of this Document

This document is an Internet-Draft.  Internet-Drafts are
working documents of the Internet Engineering Task Force
(IETF), its areas, and its working groups.  Note that other
groups may also distribute working documents as Internet-

Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced or made obsolete by
other documents at any time.  It is inappropriate to use
Internet-Drafts as reference material or to cite them other
than as works in progress.

Distribution of this document is unlimited.  Please send
comments to clifford.lynch@ucop.edu and cecilia@well.com.

This document does not specify a standard; it is purely

0. Abstract

A system for Uniform Resource Names (URNs) must be capable
of supporting identifiers from existing widely-used naming
systems.  This document discusses how three major
bibliographic identifiers (the ISBN, ISSN and SICI) can be
supported within the URN framework and the currently
proposed syntax for URNs.

                                                    [Page 1]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

1. Introduction

The ongoing work of several IETF working groups, most
recently in the Uniform Resource Names working group, has
culminated the development of a syntax for Uniform Resource
Names (URNs).   The functional requirements and overall
framework for Uniform Resource Names are specified in RFC
1737 [Sollins & Masinter] and the current proposal for the
URN syntax is draft-ietf-urn-syntax-04.txt [Moats].

As part of the validation process for the development of
URNs the IETF working group has agreed that it is important
to demonstrate that the current URN syntax proposal can
accommodate existing identifiers from well managed
namespaces.  One such well-established infrastructure for
assigning and managing names comes from the bibliographic
community.  Bibliographic identifiers function as names for
objects that exist both in print and, increasingly, in
electronic formats.  This Internet draft demonstrates the
feasibility of supporting three representative bibliographic
identifiers within the currently proposed URN framework and

Note that this document does not purport to define the
"official" standard way of doing so; it merely demonstrates
feasibility.  It has not been developed in consultation with
the standards bodies and maintenance agencies that oversee
the existing bibliographic identifiers.  Any actual Internet
standard for encoding these bibliographic identifiers as
URNs will need to be developed in consultation with the
responsible standards bodies and maintenance agencies.

In addition, there are several open questions with regard to
the management and registry of Namespace Identifiers (NIDs)
for URNs.  For purposes of illustration, we have used the
three NIDs "ISBN", "ISSN" and "SICI" for the three
corresponding bibliographic identifiers discussed in this
document.  While we believe this to be the most appropriate
choice, it is not the only one.  The NIDs could be based on
the standards body and standard number (e.g. "US-ANSI-NISO-
Z39.56-1997" rather than "SICI").  Alternatively, one could
lump all bibliographic identifiers into a single
"BIBLIOGRAPHIC" name space, and structure the namespace-

                                                   [Page 2]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

specific string to specify which identifier is being used.
We do not believe that these are advantageous approaches,
but must wait for the outcome of namespace management
discussions in the working group.

For the purposes of this document, we have selected three
major bibliographic identifiers (national and international)
to fit within the URN framework.  These are the
International Standard Book Number (ISBN) [ISO1], the
International Standard Serials Number (ISSN) [NISO1,ISO2,
ISO3], and the Serial Item and Contribution Identifier
(SICI) [NISO2].  ISBNs are used to identify monographs
(books).  ISSNs are used to identify serial publications
(journals, newspapers) as a whole.  SICIs augment the ISSN
in order to identify individual issues of serial
publications, or components within those issues (such as an
individual article, or the table of contents of a given
issue).  The ISBN and ISSN are defined in the United States
by standards issued by the National Information Standards
Organization (NISO) and also by parallel international
standards issued under the auspices of the International
Organization for Standardization (ISO).  NISO is the ANSI-
accredited standards body serving libraries, publishers and
information services.  The SICI code is defined by a NISO
document in the United States and does not have a parallel
international standards document at present.

Many other bibliographic identifiers are in common use (for
example, the CODEN, numbers assigned by major bibliographic
utilities such as OCLC and RLG, national library numbers
such as the Library of Congress Control Number) or are under
development.  While we do not discuss them in this document,
many of these will also need to be supported within the URN
framework as it moves to large scale implementation.  The
issues involved in supporting those additional identifiers
are anticipated to be broadly similar to those involved in
supporting ISBNs, ISSNs, and SICIs.

2. Identification vs. Resolution

It is important to distinguish between the resource
identified by a URN and the resources that can reasonably be
provided when attempting to resolve an identifier.  For

                                                    [Page 3]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

example, the ISSN 0040-781X identifies the popular
"Time".  All of it, every issue for from the start of
publication to present.  Resolving such an identifier should
not result in the equivalent of hundreds of thousands of
pages of text and photos being dumped to the user's machine.
It is more reasonable for ISSNs to resolve to a navigational
system, such as an HTML-based search form, so the user may
select issues or articles of interest.  ISBNs and SICIs, on
the other hand, do identify finite, manageably-sized
objects, but they may still be large enough that resolution
to a hierarchical system is appropriate.

In addition, the materials identified by an ISSN, ISBN or
SICI may exist only in printed or other physical form, not
electronically.  The best that a resolver may be able to
offer is information about where to get the physical
resource, such as library holdings or a bookstore or
publisher order form.  The URN Framework provides resolution
services that may be used to describe any differences
between the resource identified by a URN and the resource
that would be returned as a result of resolving that URN.

3. International Standard Book Numbers

3.1 Overview

An International Standard Book Number (ISBN) identifies an
edition of a monographic work.  The ISBN is defined by the
standard NISO/ANSI/ISO 2108:1992 [ISO 1]

Basically, an ISBN is a ten-digit number (actually, the last
digit can be the letter "X" as well, as described below)
which is divided into four variable length parts usually
separated by hyphens when printed.  The parts are as follows
(in this order):

* a group identifier which specifies a group of publishers,
based on national, geographic or some other criteria,

* the publisher identifier,

                                                   [Page 4]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

* the title identifier,

* and a modulus 11 check digit, using X in lieu of 10.

The group and publisher number assignments are managed in
such a way that the hyphens are not needed to parse the ISBN
unambiguously into its constituent parts.  However, the ISBN
is normally transmitted and displayed with hyphens to make
it easy for human beings to recognize these parts without
having to make reference to or have knowledge of the number
assignments for group and publisher identifiers.

3.2 Encoding Considerations

Embedding ISBNs within the URN framework presents no
particular coding problems, since all of the characters that
can appear in an ISBN are valid in the identifier segment of
the URN.  %-encoding is never needed.

Example: URN:ISBN:0-395-36341-1

For the ISBN namespace, some additional equivalence rules
are appropriate.  Prior to comparing two ISBN URNs for
equivalence, it is appropriate to remove all hyphens, and to
convert any occurrences of the letter X to upper case.

3.3 Additional considerations

The ISBN standard and related community implementation
guidelines define when different versions of a work should
be assigned the same or differing ISBNs.  In actuality,
however, practice varies somewhat depending on publisher as
to whether different ISBNs are assigned for paperbound vs.
hardbound versions of the same work, electronic vs. printed
versions of the same work, or versions of the same work
published for example in the US and in Europe.  The choice
of whether to assign a new ISBN or to reuse an existing one
when publishing a revised printing of an existing edition of
a work or even a revised edition of a work is somewhat
subjective.  Practice varies from publisher to publisher
(indeed, the distinction between a revised printing and a
new edition is itself somewhat subjective).  The use of

                                                    [Page 5]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

ISBNs within the URN framework simply reflects these
existing practices.  Note that it is likely that an ISBN URN
will often resolve to many instances of the work (many

4. International Standard Serials Numbers

4.1 Overview

International Standard Serials Numbers (ISSN) identify a
work that is being published on a continued basis in issues;
they identify the entire (often open-ended, in the case of
an actively published) work.  ISSNs are defined by the
standards ISO 3297:1986 [ISO 2] and ISO/DIS 3297 [ISO 3] and
within the United States by NISO Z39.9-1992 [NISO 1].  The
ISSN International Centre is located in Paris and
coordinates a network of regional centers.  The National
Serials Data Program within the Library of Congress is the
US Center of this network.

ISSNs have the form NNNN-NNNN where N is a digit, the last
digit may be an upper case X as the result of the check
character calculation.  Unlike the ISBN the ISSN components
do not have much structure; blocks of numbers are passed out
to the regional centers and publishers.

4.2 Encoding Considerations

Again, there is no problem representing ISSNs in the
namespace-specific string of URNs since all characters valid
in the ISSN are valid in the namespace-specific URN string,
and %-encoding is never required.

Example: URN:ISSN:1046-8188

Supplementary comparison rules are also appropriate for the
ISSN namespace.  Just as for ISBNs, hyphens should be
dropped prior to comparison and occurrences of 'x'
normalized to uppercase.

                                                    [Page 6]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

4.3 Additional Considerations

The ISSN standard and related community implementation
guidelines specify when new ISSNs should be assigned vs.
continuing to use an existing one.  There are some
publications where practice within the bibliographic
community varies from site to site, such as annuals or
annual conference proceedings.  In some cases these are
treated as serials and ISSNs are used, and in some cases
they are treated as monographs and ISBNs are used.  For
example SIGMOD Record volume 24 number 2 June 1995 contains
the Proceedings of the 1995 ACM SIGMOD International
Conference on Management of Data.  If you subscribe to the
journal (ISSN 0163-5808) this is simply the June issue.  On
the other hand you may have acquired this volume as the
conference proceedings (a monograph) and as such would use
the ISBN 0-89791-731-6 to identify the work.  There are also
varying practices within the publishing community as to when
new ISSNs are assigned due to the change in the name of a
periodical (Atlantic becomes Atlantic Monthly); or when a
periodical is published both in printed and electronic
versions (The New York Times).  The use of ISSNs as URNs
will reflect these judgments and practices.

5. Serial Item and Contribution Identifiers

5.1 Overview

The standard for Serial Item and Contribution Identifiers
(SICI) has recently been extensively revised and is defined
by NISO/ANSI Z39.56-1997 [NISO 2].  The maintenance agency
for the SICI code is the UnCover Corporation.

SICI codes can be used to identify an issue of a serial, or
a specific contribution (i.e., an article, or the table of
contents) within an issue of a serial.  SICI codes are not
assigned, they are constructed based on information about
the issue or issue component in question.

The complete syntax for the SICI code will not be discussed
here; see NISO/ANSI Z39.56-1997 for details.  However an
example and brief review of the major components is needed

                                                    [Page 7]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

to understand the relationship with the ISSN and how this
identifier differs.  An example of a SICI code is:


The first nine characters are the ISSN identifying the
serial title.  The second component, in parentheses, is the
chronology information giving the date the particular serial
issue was published.  In this example that date was January
1, 1996.  The third component, 157:1, is enumeration
information (volume, number) on the particular issue of the
serial.  These three components comprise the "item segment"
of a SICI code.  By augmenting the ISSN with the chronology
and/or enumeration information, specific issues of the
serial can be identified.  The next segment, <62:KTSW>,
identifies a particular contribution within the issue.  In
this example we provide the starting page number and a title
code constructed from the initial characters of the title.
Identifiers assigned to a contribution can be used in the
contribution segment if page numbers are inappropriate.  The
rest of the identifier is the control segment, which
includes a check character.  Interested readers are
encouraged to consult the standard for an explanation of the
fields in that segment.

5.2 Encoding Considerations

The character set for SICIs is intended to be email-
transport-transparent, so it does not present major
problems.  However, all printable excluded and reserved
characters from the URN syntax draft are valid in the SICI
character set and must be %-encoded.

Example of a SICI for an issue of a journal


For an article contained within that issue


                                                    [Page 8]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

Special equivalence rules for SICIs are not appropriate for
definition as part of the namespace and incorporation in
areas such as cache management algorithms.  These are best
left to resolver systems which try to determine if two SICIs
refer to the same content.  Consequently, we do not propose
any specific rules for equivalence testing through lexical

5.3 Additional Considerations

Since the serial is identified by an ISSN, some of the
ambiguity currently found in the assignment of ISSNs carries
over into SICI codes.  In cases where an ISSN may refer to a
serial that exists in multiple formats, the SICI contains a
qualifier that specifies the format type (for example,
print, microform, or electronic).  SICI codes may be
constructed from a variety of sources (the actual issue of
the  serial, a citation or a record from an abstracting
service) and, as such are based on the principle of using
all available information, so there may be multiple SICI
codes representing the same article [NISO2, Appenidx D].
For example, one code might be constructed with access to
both chronology and enumeration (that is, date of issue and
volume, issue and page number), another code might be
constructed based only on enumeration information and
without benefit of chronology.  Systems that use SICI codes
employ complex matching algorithms to try to match SICI
codes constructed from incomplete information to SICI codes
constructed with the benefit of all relevant information.

6. Security Considerations

This document proposes means of encoding several existing
bibliographic identifiers within the URN framework.  It does
not discuss resolution; thus questions of secure or
authenticated resolution mechanisms are out of scope.  It
does not address means of validating the integrity or
authenticating the source or provenance of URNs that contain
bibliographic identifiers.  Issues regarding intellectual
property rights associated with objects identified by the
various bibliographic identifiers are also beyond the scope
of this document, as are questions about rights to the
databases that might be used to construct resolvers.

                                                    [Page 9]

INTERNET DRAFT:Bibliographic Identifiers as URNs     3/1997

7. References

[ISO1] NISO/ANSI/ISO 2108:1992 Information and documentation
       -- International standard book number (ISBN)
[ISO2] ISO 3297:1986 Documentation -- International standard
       serial numbering (ISSN)
[ISO3] ISO/DIS 3297 Information and documentation --
       International standard serial numbering (ISSN)
       (Revision of ISO 3297:1986)
[Moats] R. Moats, "URN Syntax" draft-ietf-urn-syntax-
       04.text. March 1997
[NISO 1] NISO/ANSI Z39.9-1992 International standard serial
       numbering (ISSN)
[NISO 2] NISO/ANSI Z39.56-1997 Serial Item and Contribution
[Sollins & Masinter] K. Sollins and L. Masinter, "Functional
       Requirements for Uniform Resource Names", RFC 1737
       December 1994.

8. Author's Addresses

Clifford Lynch
University of California Office of the President
300 Lakeside Drive, 8th floor
Oakland CA 94612-3550

Cecilia Preston
Preston & Lynch
PO Box 8310
Emeryville, CA 94662

Ron Daniel Jr.
Advanced Computing Lab, MS B287
Los Alamos National Laboratory
Los Alamos, NM, 87545
voice: +1 505 665 0597
fax: +1 505 665 4939

                                                   [Page 10]