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

Versions: 00 01                                                         
Network Working Group                                       Juha Hakala
Internet-Draft                              Helsinki University Library
Category: Informational                                  28 August 2001
Expires: 28 February 2002

            Using Serial Item and Contribution Identifiers as
                         Uniform Resource Names

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

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-Drafts.

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

     The list of current Internet-Drafts can be accessed at

     The list of Internet-Draft Shadow Directories can be accessed at

This Internet-Draft will expire on 28 February 2002.


This document discusses how Serial Item and Contribution Identifiers
(SICIs; persistent and unique identifiers for serial issues and
contributions such as articles) can be supported within the URN
framework and the syntax for URNs defined in RFC 2141 [Moats]. Much of
the discussion below is based on the ideas expressed in RFC 2288
[Lynch]. Chapter 5 contains a URN namespace registration request
modelled according to the template in RFC 2611 [Daigle et al.].

1. Introduction

As part of the validation process for the development of URNs the IETF
working group agreed that it is important to demonstrate that the
current URN syntax proposal can accommodate existing identifiers from
well-established namespaces.  One such 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.  RFC 2288 [Lynch et. al.]
investigated the feasibility of using three identifiers (ISBN, ISSN and
SICI) as URNs.

SICI is an American national standard defined by NISO/ANSI Z39.56-1996
[NISO]. The need to develop a new version of the standard is at present
being investigated by NISO.

RFC 2288 does not û and it was not the aim of its authors û to analyse
how SICI-based URNs can actually be resolved. This text will specify one
solution to this question. There may be other, complementary resolution

Generally, the difficulty of designing a URN resolution service is
dependent on two factors:

* Is the identifier dumb, or does it provide a hint on where to find a
resolution service?

* How many potential resolution services are there?

ISBN (International Standard Book Number) is a good example of an
intelligent identifier. Analysis of the ISBN will reveal not only the
region where the ISBN has been assigned, but also the publisher who is
responsible for the book. Resolution of ISBN-based URNs can be
decentralised to national bibliography databases, maintained by the
national libraries. If the ISBN was a dumb identifier, this would be

International Standard Serial Number (ISSN) is a dumb identifier. It
does not have a publisher identifier; serials published by a certain
company get seemingly random ISSNs. Although ISSNs are allocated to
regional agencies in blocks, which gives the system some "intelligence",
a resolution service should not rely on these blocks, but use the global
ISSN database. It contains a bibliographic description of every
periodical that has received an ISSN. Thus, it is easy to resolve ISSN-
based URNs even though the identifier itself does not help in localising
the resolution service.

SICI is based on ISSN (see below for a description of its syntax). Like
ISSN, it is therefore a dumb identifier. But there is not, and will
never be, a global SICI database, which would contain bibliographic
information about every serial issue and/or article published in the
world. Most articles will not be catalogued at all, and the existing
bibliographic information about articles is dispersed into a large
number of databases maintained by publishers, libraries and other
information intermediaries. Although it might be technically possible to
merge records from these databases into a union catalogue, in practice
such an enterprise is not politically possible.

As a "dumb" identifier with a large and ever growing number of potential
resolution services SICI poses interesting challenges to the design of
the URN resolution process.

Generally, a combination of dumb identifier and multiple resolution
services is a problem, since there is no simple way of finding out which
resolution service is the correct one. A gateway service is needed for
providing this valuable information. Below we propose that for SICI-
based URNs, the global ISSN database will be capable of acting as a link
between the user and the resolution service.

The registration request for acquiring a Namespace Identifier (NID)
"SICI" for Serial Item and Contribution Identifiers has been written by
the National Library of Finland on behalf of the National Information
Standards Organization (NISO). The request is included in chapter 5 of
this text.

The document at hand is part of a global co-operation of the national
libraries to foster identification of electronic documents in general
and utilisation of URNs in particular. This work is co-ordinated by a
working group established by the Conference of Directors of National
Libraries (CDNL).

We have used the URN Namespace Identifier "SICI" for the Serial Item and
Contribution Identifiers in examples below.

2. Identification vs. Resolution

As a rule the SICIs identify finite, manageably-sized objects, but these
objects may still be large enough so that resolution to a hierarchical
system, such as all articles published in a serial issue, is

The materials identified by a SICI may exist only in printed or other
physical form, not electronically. The best that a resolver service will
be able to offer in this case is bibliographic data from the database
providing resolution services, including information about where the
physical resource is stored in the owner institution's holdings.

3. Serial Item and Contribution Identifier

3.1 Overview

The Serial Item and Contribution Identifier (SICI) standard defines a
variable length code that provides unique identification of serial items
(e.g., issues) and the contributions (e.g., articles) contained in a
serial title. SICI is specified in NISO/ANSI Z39.56-1996 [NISO2]. Like
other NISO standards, the SICI document is available for free in the Web.

SICI is based on ISSN (International Standard Serial Number), but
augments it extensively. SICI is a combination of three segments, all of
which are required:

Item segment; the data elements needed to describe the serial item such
as serial issue (ISSN, Chronology, Enumeration)

Contribution segment, the data elements needed to identify contributions
within an item (Location, Title Code)

Control segment, the data elements needed to record those administrative
elements that determine the validity, version, and format of the SICI
code representation.

RFC 2288 provides the following example:


   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) for 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

SICI can be seen as a logical extension of the ISSN to the items and
individual contributions that make up a serial's hierarchical structure.
The current version of the SICI does have some limitations; it does not
allow identification of subsections of an article such as paragraphs or
diagrams. If deemed necessary, the functionality needed for article
subsection identification could be added to the standard.

The current version of SICI guarantees uniqueness in most situations;
however, the standard does not always differentiate between multiple
variant formats in which an electronic article may be published. For
instance, variants of a digitised article published in PDF and HTML
formats will receive the same SICI, provided that the ISSN is the same.

According to the rules of the ISSN centre, ISSN numbers can be applied
retrospectively to old periodicals. If the original printed document has
an ISSN, the same identifier is also valid for the digitised version.
ISSN guidelines formulate this principle in the following way:

A reproduction is a copy of an item and intended to function as a
substitute for that item. The reproduction may be in a different medium
from the original but it is not a different edition in itself. The ISSN
assigned to the original is valid for the reproduction, a new ISSN is not
assigned to the reproduction.

ISSN numbers are assigned by regional agencies, which receive ISSN
blocks from the ISSN International Centre. SICI usage is not dependent
on such formal agencies; the aim is that once ISSN is known, SICI codes
can be created, manually or by computer program, by publishers,
libraries, document delivery services or even by individual users.

Given the complexity of SICI codes, the recommended practice is to
automate the SICI creation process. If an article is structured enough,
all elements of SICI can be extracted from the document. A tool capable
of this has been built by the E.U. project DIEPER; this tool, of course,
only works properly if the document is structured in the way the DIEPER
project recommends. Another, less challenging option is a SICI
generator, which builds syntactically correct SICIs including the check
character if the basic ingredients are typed in manually.

3.2 Encoding Considerations and Lexical Equivalence

RFC 2288 contains the following simple and yet sufficient analysis of
SICI encoding:

   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 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:


   Equivalence rules for SICIs are not appropriate for definition as
   part of the namespace and incorporation in areas such as cache
   management algorithms.  It is 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 manipulation.

3.3 Resolution of SICI-based URNs

Since ISSN is a dumb code, SICI does not contain any explicit hint on
where to find the URN resolution service or services. However, an
efficient and global resolution service can be accomplished by using the
ISSN register as a way station. In spring 2001, the ISSN register
contained about one million bibliographic records describing serials,
including thousands of electronic journals. There are several other
databases, which contain hundreds of thousands of serial records, but
the ISSN register has the best coverage.

The first step in resolving a SICI-based URN is a query to the ISSN
register. The SICI resolution service in the ISSN register will parse
the SICI code in order to extract the ISSN from it.

ISSN will then be used as a search key for retrieving the bibliographic
record of the serial from the ISSN register.

Currently the ISSN register already contains thousands of records
describing electronic journals. These records contain the URL of the
serial's home page.

This URL is appropriate for resolving the URN based on the ISSN of the
periodical. The mechanism for resolving such URNs via the ISSN register
has been specified in RFC 3044 [Rozenfeld]. The ISSN International
Centre has already built a demonstration URN resolution service for
ISSN-based URNs into their present information system.

In order to resolve SICI-based URNs, a new data element has to be added
into the records in the ISSN register. This data element would contain
the network address (URL) of the database, which holds the article
required and/or bibliographic information about it. It must also be
possible to specify volumes and if necessary issues which are included
in the database within this data element. The data element should be
repeatable, since the same article may be available from multiple
sources. For instance, the publisher, Library of Congress
(http://www.loc.gov/), JSTOR (http://www.jstor.org/) and a number of
host services such as EBSCO (http://www.ebsco.com/home/) may all have a
copy of the same resource.

The SICI resolution service built into the ISSN register will check if
database address information is available in the bibliographic record of
the serial. Then it makes sure that the volume and/or issue needed is
available via the service. If this is the case, the application will
make the query, receive the result û article or bibliographic
information about it - and pass it on to the user.

The functionality described above was implemented in co-operation
between the ISSN International Centre and the E.U. project DIEPER
(http://gdz.sub.uni-goettingen.de/dieper/). The SICI resolution service
is an extension of the service built for resolving ISSN-based URNs. By
March 2001 a demonstrator service via which several of the databases
maintained by the project partners could be accessed was released for
internal use within the project. The ISSN IC and project partners wish
to maintain the service also after the formal end of the project.

Discussions about adding the new data element into bibliographic records
in the ISSN register are under way.

Please note that the discussion herein applies to SICIs assigned to
serial contributions. Since serial items (issues) have seldom been
described or digitised as such, a search by serial item SICI will in
practice be expanded into retrieval of all contributions (articles)
within the serial item (issue) in question.

If a resolution service for the resource at hand does not exist, or the
user is not authorised to utilise it, he/she may get the bibliographic
description of the serial from the ISSN register.

3.4 Additional considerations

Electronic journals have rapidly become very popular in scientific
publishing. The main reasons for this are the emergence of viable
business models (e.g. licensing) and the birth of a reliable and
efficient delivery mechanism (the Web).

New content is being added via two different channels. A significant
number of scientific journals is published in electronic form, usually
alongside a printed version. On the other hand, old printed volumes are
digitised and made available in electronic form. Digitisation is done by
development projects such as DIEPER, established services such as JSTOR,
or publishers - for instance Elsevier is digitising all printed journals
the company has published.

Reliable linking of articles to references and bibliographic data about
the articles is an important issue. URLs are as of this writing the most
common means used for linking, but their reliability is low; average
lifetime for a URL is estimated to be two years.

A more reliable linking mechanism than URLs is urgently needed. Many
scientific publishers are already using Digital Object Identifiers (DOI)
for their materials. DOI resolution service is based on Handle system,
which is "a comprehensive system for assigning, managing, and resolving
persistent identifiers, known as "handles," for digital objects and
other resources on the Internet" (see
http://www.handle.net/introduction.html). Handles can be used as Uniform
Resource Names(URNs).

URN is both an identifier and a non-commercial and technically advanced
resolution service. Due to the co-operation of the ISSN International
Centre the URN resolution service for articles outlined in this Internet
standard is global, and can accommodate an unlimited number of article
services located anywhere in the world.

For instance, in order to establish URN-based links to articles
digitised in JSTOR service, a number of steps are necessary. First, each
article must be identified by SICI, and these SICIs must be indexed in
the JSTOR database. Second, bibliographic records of JSTOR journals in
the ISSN register must all be enriched with a link to the JSTOR search
interface and volume/issue information. For instance, the bibliographic
record describing the journal "Ecology" must contain the information
that volumes 1-77 (1920-1996) are available via JSTOR. This information
may be quite volatile, and maintenance of the ISSN register must
therefore be frequent and efficient.

Apart from modification of the data, some programming work is needed.
Due to the work done in the DIEPER project, the ISSN register already
has the functionality needed for resolving SICI-based URNs. Adding the
required functionality into the JSTOR database may or may not be
difficult depending on the system architecture; in DIEPER some partners
were able to implement the required functionality quite easily.

Since the Web browsers do not support URN resolution yet, the final step
in enabling resolution of URN-based SICIs is installation of the browser
plug-in developed by the ISSN International Centre.

For various reasons, one article may be available in several locations.
Every article copy may have a different set of users who are allowed
access to it. For instance, a copy acquired by a national library via
legal deposit may only be available within the library premises.

Making the links context sensitive û provide only those links that
"work" for a user is a challenge. OpenURL framework [Van de Sompel]
provides a means for sensitive linking. As of this writing OpenURL is
rapidly gaining popularity, and there are already a few integrated
library systems which support it. The ISSN register may in the future
support OpenURL usage; this would be very valuable when the same
resource (article) is available from several sources, which have
different user population.

In their present form the URN resolution services provided via the ISSN
register suit those services best, which are available in public domain,
and are reasonably stable. Numerous digitisation projects such as DIEPER
are currently making printed articles available in the Web in digital

An additional benefit of coding the needed location and volume
information into the ISSN register would be that this database then
could also serve as a global registry of serial digitisation efforts.
Such a register is badly needed to avoid duplicate work.

Since the number of SICI resolution services will eventually be high,
the capacity of the server on which the ISSN register runs and its
network connection may become a bottleneck, especially if the articles
were delivered via the ISSN server to the users. Setting up mirror sites
would in this case be the most efficient means for load control and
balancing. Technically the setting up of mirror sites is not difficult.
The ISSN register contains approximately a million bibliographic
records, and is therefore not a very large database.

4. Security Considerations

This document proposes means of encoding and using Serial Item and
Contribution Identifiers within the URN framework. This document does
not discuss resolution except at a generic level; thus questions of
secure or authenticated resolution mechanisms in the ISSN register or in
actual resolution services are out of scope.  This text does not address
means of validating the integrity or authenticating the source or
provenance of URNs that contain SICIs.  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.

5. Namespace registration

URN Namespace ID Registration for the Serial Item and Contribution
Identifier (SICI)

Namespace ID:


SICI is a well-established acronym for Serial Item and Contribution
Identifiers; giving this NID for any other system would cause a lot of

This namespace ID has already been used in SICI-based URNs in the E.U.
project DIEPER.

Registration Information:

Version: 1
Date: 2001-08-28

Declared registrant of the namespace:

Name: Patricia Harris
E-mail: pharris@niso.org
Affiliation: National Information Standards Organisation
Address: 4733 Bethesda Avenue, Suite 300, Bethesda, MD 20814

Declaration of syntactic structure:

Each SICI contains three segments:

Item segment; the data elements needed to describe the serial item such
as serial issue (ISSN, Chronology, Enumeration)

Contribution segment, the data elements needed to identify contributions
within an item (Location, Title Code)

Control segment, the data elements needed to record those administrative
elements that determine the validity, version, and format of the SICI
code representation.



SICI codes can be generated and parsed by computer programs.

Relevant ancillary documentation:

SICI is an American national standard defined by NISO/ANSI Z39.56-1996
[NISO2]. A new version of the standard is currently under development.

Identifier uniqueness considerations:

SICI codes will almost always be unique. Since SICI is based on ISSN,
articles from different journals will definitely never get the same
SICI. Since enumeration and chronology information must also be given,
articles and other contributions published in different volumes and
issues will also never get the same SICI.

SICIs may not be unique if and only if:

If two or more contributions are published on the same page(s) and if
they have similar enough titles (the first letter of each word is the

In a single issue of an electronic journal (which lacks page numbers)
there are two or more contributions with titles similar enough.

If there are several technical variants of an electronic serial
contribution (multiple formats, multiple resolutions) the current
version of SICI will not make any difference between these variants. In
this case the intellectual content will usually be the same, but layout
will differ from one version to another.

The new version of the SICI standard will be enhanced in order to
diminish the risk of non-unique SICIs.

Identifier persistence considerations:

Once assigned, SICI will never change. The same SICI will not be used
again for other serial items and contributions.

Process of identifier assignment:

There will not be a national, regional or international agency governing
the SICI assignment process. Publishers, libraries or other information
intermediaries will create SICIs when needed. The most important
prerequisite is that the journal must have an ISSN.

Although SICI assignment is decentralised, the national ISSN agencies
and the ISSN International Centre may support publishers and other
interested parties in SICI implementation.

SICI can - and should - be built via automated means. If the source
document such as article is sufficiently structured, SICI can be
generated without human involvement. Another option is a semi-automated
process, in which a human user types in the relevant data elements, and
the application takes care of building the code.

Process for identifier resolution:

Resolution will take place in two steps as defined in chapter 3.3. First
the ISSN register is used for finding the location of the resolution
service(s) for the serial and volume at hand. Using the linking
information stored in the serial's bibliographic record, the correct
resolution service is contacted, and the requested resource is delivered
to the user.

Rules for Lexical Equivalence:

We do not propose any specific rules for equivalence testing through
lexical manipulation.

Conformance with URN Syntax:

According to the RFC 2288:

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 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:


Validation mechanism:

Validity of a SICI string can be checked by modulus 37 check digit.



6. References

[Daigle et al.]: Daigle, L., van Gulik, D., Iannella, R. & Faltstrom,
P.: URN Namespace Definition Mechanisms, RFC2611, June 1999.

[Lynch] Lynch, C., Using Existing Bibliographic Identifiers as Uniform
Resource Names, RFC 2288, February 1998

[Moats] Moats, R., URN Syntax, RFC 2141, May 1997.

[NISO] NISO/ANSI Z39.56-1996 Serial Item and Contribution Identifier.
Electronic resource, available at http://www.techstreet.com/cgi-

[Rozenfeld] Rozenfeld, S., Using The ISSN (International Serial Standard
Number) as URN (Uniform Resource Names) within an ISSN-URN Namespace,
RFC 3044, January 2001.

[Van de Sompel] Van de Sompel, Herbert & Beit-Arie, Oren: Open Linking
in the Scholarly Information Environment Using the OpenURL Framework. D-
Lib Magazine, March 2001. Electronic resource, available at

7. Authors' Address

   Juha Hakala
   Helsinki University Library - The National Library of Finland
   P.O. Box 26
   FIN-00014 Helsinki University

   E-mail: juha.hakala@helsinki.fi

8.  Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an