Digital Object Identifier - DOIs

ANSI/NISO Z39.xx-199x 

Digital Object Identifier 

Status: 

A Draft American National Standard 

Developed by the 

National Information Standards Organization 

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About NISO Draft Standards 

This is a draft standard and subject to change. To learn the current status of this 

proposed standard contact the NISO Office: 4733 Bethesda Avenue, Suite 300, Bethesda, MD 

20814 USA; Telephone: 301-654-2512; Fax: 301-654-1721; Internet nisohq@niso.org. 

NISO standards are developed by the Standards Committees of the National 

Information Standards Organization. A rigorous review process includes offering each NISO 

voting member and other interested parties an opportunity to review the proposed standard. In 

addition, approval requires verification by the American National Standards Institute that its 

requirements for due process, consensus, and other criteria for approval have been met by 

NISO; NISO standards thus also become American National Standards. 

This standard may be revised or withdrawn at any time. Purchasers may receive 

current information on all NISO standards by calling or writing the National Information 

Standards Organization. 

©1997 National Information Standards Organization 

This draft standard may be photocopied for noncommercial purposes to facilitate the review 

and approval process. 

Address inquiries to NISO, 4733 Bethesda Avenue, Suite 300, Bethesda, MD 20814; 

nisohq@niso.org; Telephone: 301-654-2512; Fax: 301-654-1721. 

To Order Any NISO Standard Contact: 

NISO Press Fulfillment, P.O. Box 338, Oxon Hill, MD 20750-0338 USA 

Telephone: 1-800-282-6476 or 301-567-9522 

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Contents 

Foreword 

Background 

Goals 

Elements of the DOI String 

The DOI and Metadata 

The DOI in Context (DOI System, Handle System, IDF) 

Character Set Issues 

1. Introduction 

1.1 Purpose 

1.2 Scope 

2. Standards and References 

2.1 Referenced Standards 

2.2 Secondary Standards and References 

2.3 Other Standards and References 

3. Definitions 

4. Format and Characteristics of the DOI 

4.1 Prefix 

4.2 Suffix 

Maintenance Agency 

APPENDIX A 

Designation of Maintenance Agency 

APPENDIX B 

Examples 

APPENDIX C 

Related Standards and References 

APPENDIX D 

Application Issues 

Location and Presentation of the DOI 

Representation to End Users 

Table 1 – Mandatory Encoding 

Table 2 – Recommended Encoding 

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Foreword 

This foreword is not part of the American National Standard for the Digital Object Identifier 

(DOI), ANSI/NISO Z39.xx-199x. It is included for information only. 

This standard defines the syntax for the Digital Object Identifier (DOI). The Digital Object 

Identifier (DOI) system is an identification system for intellectual property in the digital 

environment. Developed by the International DOI Foundation on behalf of the publishing 

industry, its goals are to provide a framework for managing intellectual content including such 

activities such as linking customers with content owners, facilitating electronic commerce, and 

enabling automated copyright management. 

Background 

Some history on the development of this draft standard is needed to understand how and why 

the draft standard appears in its present form. 

DOI System Background 

The Internet is a new environment for commerce of information, and requires new enabling 

technologies to provide services and to protect both customer and publisher. Systems must be 

developed to identify, authenticate, and protect content to insure that what the customer is 

requesting is what is being delivered. At the same time, the rights owner of the information 

must be sure that copyright in content is respected and protected. 

In considering the new systems required international publishers realized that a first step would 

be the development of an identification system to be used for content in the digital 

environment. Such a system was launched at the Frankfurt Book Fair in October 1997: the 

Digital Object Identifier (DOI) system provides a unique identification mechanism for content, 

and also a way to link users of the materials to the rights holders (or their agents) to facilitate 

automated digital commerce in the new digital environment. 

NISO Involvement and Role of the International DOI Foundation (IDF) 

The ongoing management of the DOI System is handled by an international, not-for-profit, 

membership-based organization called the International DOI Foundation with offices in the 

United States and Geneva, Switzerland. The Foundation is responsible for licensing Directory 

Managers/Registration Agencies and technology providers, for setting policy for the system, 

and for encouraging development of the related enabling technologies to build the 

infrastructure for electronic publishing such as copyright management systems. 

Though the DOI System was originally developed by the publishing industry, it was recognized 

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that the DOI system would have a broader scope and that it should work with established 

standard bodies as much as possible. ANSI/NISO involvement was requested in early 1998 in 

order to recognize the broader potential use of a digital object identifier and it was decided to 

develop a standard for the syntax of the DOI identifier string. 

Goals 

*Decide on the syntax for the DOI identifier string to enable DOI registration. It has been 

possible to register DOIs for quite awhile but there has been concern that the syntax had 

not been conclusively set. This standard will remedy the situation. 

*Decide on the elements of the DOI identifier string. A number of proposals were made 

to add certain elements to the DOI identifier string and the committee spent much of its 

time deciding whether to include them or not. 

*Limit the scope of the standard to the DOI identifier string. The DOI system is made up 

of a number of parts including the identifier string, the resolution mechanism and the 

Directory. This standard addresses only the syntax for the identifier string so the actual 

standard is brief. 

While limiting itself to the DOI identifier string, the Syntax Committee took into account 

the wider context of the DOI system, the Handle system, the International DOI 

Foundation and the Internet. In order to provide further information about this context 

there is this Forward and a number of Appendices; however, these are not part of the 

Standard. They do provide important information and references for understanding the 

DOI system, how the DOI is being used, how it relates to other standards and the Internet 

and where to get more information. 

Elements of the DOI String 

The DOI string is made up of a Prefix and Suffix. The Registration Agency assigns the 

Prefix while the Registrant determines the Suffix. There were a number of proposals to 

add elements to the Prefix and Suffix, the most important being the identifier, or 

bracketed, code for the Suffix. This code would have been added in parentheses as the 

beginning of the Suffix when a standard identifier, such as the ISRC, ISBN or SICI, was 

used. This raised the issue of whether the DOI would be “dumb” or “intelligent”, i.e. 

whether the DOI string would contain any meaningful data about the thing it identified. 

The DOI string was originally created to be a “dumb” number and adding the identifier 

code would have fundamentally changed the nature of the DOI string. So, a conscious 

decision was made to leave out the identifier code and keep the DOI string a dumb 

number. However, this decision raised many important issues and highlighted the 

importance of metadata in the DOI system. 

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The DOI and Metadata 

The DOI in Context (DOI System, Handle System, IDF) 

The DOI System is an implementation of the Handle System, developed by the Corporation 

for National Research Initiatives (CNRI). The DOI System is managed by the International 

DOI Foundation, which sets policies, appoints service providers and ensures the successful 

operation of the System. 

Character Set Issues 

The Handle System allows any Unicode character to be used. However, considering the 

current and foreseeable application environment for DOIs, the Committee decided that DOIs 

should be expressible in 7-bit ASCII. This same decision was taken in ANSI/NISO Z39.56- 

1996, Serial Item and Contribution Identifier (SICI). 

The one excluded character is “space”(%20 hexadecimal). This is excluded because it signifies 

the end of a DOI string. 

There are certain issues (addressed in Appendix D) concerning character encoding when using 

DOIs in URLs that are sent via HTTP. 

NISO Voting Members 

[list] 

NISO Board of Directors 

[list] 

Standards Committee xx 

NISO acknowledges with thanks and appreciation the contributions of the following 

persons who served on NISO Standards Committee xx that drafted the proposed 

standards for the Digital Object Identifier syntax. 

[list] 

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Digital Object Identifier 

1. Introduction 

1.1 Purpose 

ANSI/NISO Z39.xx-199x defines the syntax for a unique and persistent alphanumeric 

character string called the Digital Object Identifier (DOI). The DOI is part of an identification 

system for intellectual property in the digital environment called the Digital Object Identifier 

(DOI) system. 

1.2 Scope 

This standard defines the syntax of the DOI character string, which is made up of a prefix and 

suffix and registered according to the requirements set by the International DOI Foundation 

(IDF). Policies governing the assigning and use of DOIs are determined by the IDF and are 

outside the scope of this document. 

2. Standards and References 

The Referenced Standards are those that are required to construct a DOI. Secondary 

Standards and References includes citations to documents that can be used in conjunction with 

or as part of the DOI. 

2.1 Referenced Standards 

ANSI X3.4:1986 American National Standard for Information Systems – Coded 

Character Sets – 7- Bit American National Standard Code for Information Interchange 

(7-bit ASCII) 

2.2 Secondary Standards and References 

International DOI Foundation Guidelines 

Uniform Resource Identifier (URI) 

Uniform Resource Locator (URL) 

Uniform Resource Number (URN) 

Handle System RFC 

ISSN 

ISBN 

ISWC 

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ISAN, etc 

2.3 Other Standards and References 

3. Definitions 

Creation 

An item of intellectual property; a product of human imagination and/or endeavor in which 

rights may exist. 

Digital Object Identifier system (DOI system) 

An identification system for items of intellectual property in the digital environment which 

uses a Digital Object Identifier for each item and associates with these various digital 

services. The rules of the DOI system are determined by the International DOI 

Foundation. The DOI system is an implementation of the Handle system developed by 

the Corporation for National Research Initiatives (CNRI). 

Digital Object Identifier (DOI) 

An alphanumeric character string, conforming to the rules of the DOI system, which 

uniquely identifies an item of intellectual property (a Creation). 

Directory 

A repository in which are registered and maintained DOIs, together with the digital 

services associated with each DOI, including the location of digital objects. 

Directory manager 

The entity which controls the Directory. 

DOI prefix [ = DOI prefix number] 

The unique character string issued by the Registration agency to a registrant for use as the 

prefix in the DOIs allocated by the registrant. 

DOI suffix 

The character string allocated by a registrant for use as the suffix in the DOI (uniquely 

identifying an item of intellectual property) formed using the DOI prefix held by the 

registrant. The suffix is unique within the range of DOIs specified by the DOI prefix held 

by the registrant. 

International DOI Foundation 

The body set up to support the needs of the intellectual property community in the digital 

environment by establishing and governing the DOI System, setting policies for the 

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System, appointing service providers for the System, and overseeing the successful 

operation of the System. 

Registration agency [DOI registration agency] 

One of the agencies appointed by the International DOI Foundation to register and 

allocate DOI prefixes to registrants, and which subsequently registers all DOIs issued by 

the registrant using the prefix. A registration agency uses the Directory and provides the 

information entered into the Directory. The Registration Agency may also be the 

Directory Manager in certain cases. 

Registrant 

An organization or entity which has requested and been allocated a DOI prefix by a 

Registration Agency and which subsequently allocates DOIs (constructed using that 

prefix) to items of intellectual property and registers these in the Directory, with the 

permission of, or via, the Registration Agency. 

Registration 

The act of entering into the Directory a DOI and associated information necessary for the 

DOI to be used. 

4. Format and Characteristics of the DOI 

The DOI is made up of the Prefix and the Suffix. Within the prefix are the Directory 

and the Registrant Prefix . The suffix is made up of the DOI Suffix String . The 

allowed value of the DOI is a maximum of 128 characters. 

The syntax of the DOI string is: 

. / 

Detailed explanations of each section of the DOI string follow. 

4.1 Prefix 

- Directory (required, numeric, two digits) – 

The current value of is “10”. This is currently the only allowed value. In future, other 

numbers may be assigned with the approval of NISO. The Maintenance Agency for this 

standard should be contacted regarding other values. 

Registrant’s Prefix (required, numeric, no limit) 

Separated from by “.” and no spaces. This is the number assigned to the registrant by 

the Registration Agency. 

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4.2 Suffix 

DOI Suffix String (required, any alphanumeric character except space, no limits) 

Preceded by the end “/” of the DOI Prefix, this is the actual identifier string assigned by the 

Registrant. 

Excluded character – Space (SP). Any 7-bit ASCII character can be used except “space” as 

this denotes the end of a DOI string. 

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Maintenance Agency 

The maintenance agency designated in Appendix A shall review suggestions for new data 

elements, interpret the rules prescribed by this standard, and maintain a listing of inquiries and 

responses that may be used for potential future enhancement of this standard. Questions 

concerning the implementation of this standard and requests for information should be sent to 

the maintenance agency. 

APPENDIX A 

Designation of Maintenance Agency 

This appendix is not part of the American National Standard for Digital Object Identifier (DOI), ANSI/NISO Z39.xx- 

199x. It is included for information only. 

Maintenance Agency Administered by the International DOI Foundation 

The functions assigned to the maintenance agency as specified in Section 7 will be administered 

by the International DOI Foundation. Questions concerning the implementation of this standard 

and requests for information should be sent to: 

Norman Paskin 

International DOI Foundation 

1718 Connecticut Avenue, NW 

Washington, DC 20009, USA 

Phone: 202-232-3335 x 222 

Fax: 202-745-0694 

E-Mail: n.paskin@doi.org 

APPENDIX B 

Examples 

This appendix is not part of the Digital Object Identifier (DOI), ANSI/NISO Z39.xx-199x. It is included for 

information only. 

An example of an actual DOI is: 

10.1006/(ISBN)0120001047 

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The example is made up of the ISBN for the online version of the Encyclopedia of 

Immunology from Academic Press. 

Another example shows one publisher’s approach to assigning DOIs using the SICI. 

For journals, assign the DOI based on the ISSN number; 10.1002/0002-8231 

For journal issues, assign the DOI based on the issue SICI number; e.g., 10.1002/0002- 

8231(199601)47:11.0.TX;2-J 

•. 

•. 

For journal articles, assign the DOI based on the article SICI number; e.g., 

10.1002/(SICI)0002-8231(199601)47:12.0.TX;2-2 

For journal abstracts, assign the DOI based on the abstract SICI number; e.g., 

10.1002/(SICI)0002-8231(199601)47:12.3.TX;2-U 

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APPENDIX C 

Related Standards and References 



Other Standards and References 

ANSI/NISO Z39.9-1992, International Standard Serial Numbering (ISSN) 

ANSI/NISO Z39.21-1988, Book Numbering (ISBN) 

ANSI/NISO Z39.56-1996, Serial Item and Contribution Identifier (SICI) 

Authority List of Standards 

International 

Standard 

ANSI/NISO 

Standard 

BICI 

Book Item and 

Contribution Identifier 

Proposed NISO 

development 

ISAN 

ISBN 

ISMN 

Information and 

Documentation - 

International Standard 

Audio Visual Number 

(AGICOA) 




Book Numbering 

(ISBN) 




Music Number (ISMN) 

New Work Item 

Proposal 

ISO/TC46/SC9 

N223 (1996-09- 

12) 

ISO 2108:1992 

ISO 10957:1993 

Association 

de Gestion 

Internationale 

Collective 

des Oevres 

Audiovisuelle 

s (film 

industry) 

7

ISRC Documentation - 


Recording Code 

(ISRC) 

ISRN Information and 

Documentation- 


Technical Report 

Number (ISRN) 

ISSN Documentation - 


Serial Numbering 

(ISSN) 

ISWC International Standard 

Work Code 

PII 

SICI 

Publisher Item 

Identifier 

Serial Item and 

Contribution Identifier 

(SICI) 

ISO 3901:1986 

ISO 10444:1997 

(revision of ISO 

10444:1994) 

ISO 3297:1986 

Proposed TC46 

development 

ANSI/NISO 

Z39.23-199X 

(proposed revision 

of ANSI/NISO 

Z39.23-1990) 

ANSI Z39.9:1979 

(R1984) 

ANSI/NISO 

Z39.56-199X 

(Version 2) 

(A revision of 

Z39.56-1991) 

Administered 

by IFPI - 

International 

Federation of 

Phonographic 

Industries 

(London) 

TC46 - ISO 

Technical 

Committee 

46: 

Information 

and 

Documentati 

on Standards 

http://www.el 

sevier.nl/hom 

epage/about/ 

pii 

http://sunsite. 

berkeley.edu/ 

SICI 

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APPENDIX D 

Application Issues 

Location and Presentation of the DOI 

Representation to End Users 

Using DOIs in HTML pages requires decisions as to how the DOIs will appear on the pages. 

The DOI will be represented as a normal hypertext link, so a word or phrase or title can be 

designated to appear in a specific color to signal that it is a DOI that will result in an action 

when "clicked." In many of the Prototype applications of the DOI, copyright holders chose to 

signal the use of DOIs by providing an icon or a distinctive button that would tell the user that 

the link was in fact a DOI and could be trusted. But for design purposes this is not necessary. 

Conventional hypertext links will work as well. Encoding issues complicate presentation to 

users (see Appendix D for encoding requirements). The idea is that in most cases the user 

should not need to see the DOI or could cut and paste. However, it is inevitable that in some 

cases DOIs will be printed and read and rekeyed by humans. 

Directories 

An identifier is created by the Registrant who registers it with the appropriate directory. The 

directory maintains the current location (e.g., a Uniform Resource Locator, or URL) of the 

digital object. 

Administration of the DOI 

A Registration Agency assigns the DOI Prefix and the DOI Registrant determines the Suffix. 

The components of the DOI make it unique in the world and over time, and also allow the DOI 

to be assigned by the content owner locally. Once a DOI is assigned to an object it will never 

be reassigned. There is no limit to the number of objects that can be identified by DOIs, nor is 

there a minimum size or characteristic of an object. A DOI may identify a poem, an abstract or 

an entry in a reference work as well as an article or a book, a chapter within a book or an 

image within the chapter. 

In determining what objects should be assigned DOIs, the registrant should consider what 

objects are likely to be individually bought, sold and electronically downloaded or retrieved. 

Encoding Requirements 

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There are special encoding requirements when a Digital Object Identifier is used with certain 

other identifiers. The syntax for Uniform Resource Identifiers (URIs) is very restrictive. A 

URI is a Uniform Resource Locator (URL) or a Uniform Resource Name (URN). The DOI 

operates within the URL system and conforms to the URN specification. 

Encoding Characters 

Since URL syntax conventions are more restrictive than DOI conventions, hexadecimal (%) 

encoding must be used for characters in a DOI that are not allowed, or have other meanings, in 

URLs. Hex encoding, or escaping characters, consists of substituting for the given character its 

hexadecimal value preceded by percent. Thus, # becomes %23 and 

http://dx.doi.org/10.1000/456#789 is encoded as http://dx.doi.org/10.1000/456%23789. The 

browser does not now encounter the bare #, which it would normally treat as the end of the 

URL and the start of a fragment, and so sends the entire string off to the DOI network of 

servers for resolution, instead of stopping at the #. The DOI itself does not change, merely its 

representation in a URL. A DOI that has been encoded is decoded before being sent to the 

DOI Registry. At the moment the decoding is handled by the proxy server dx.doi.org. Only 

unencoded DOIs are stored in the DOI Registry database. 

DOI creators and maintainers need to keep the following rules in mind: 

There are no character restrictions for DOI number strings per se. When DOIs are 

embedded in URLs, they must follow the URL syntax conventions, but the same DOIs 

need not follow those conventions in other contexts, e.g. inventory databases, DOI 

Registry. 

Always present DOIs in URLs in their encoded form to end users. 

The percent character (%) must always be hex encoded (%25) in any web form, batch 

input, or URL. Other excluded characters must always be hex encoded in URLs, but do 

not need to be encoded when registering the DOIs through the web forms or batch mode. 

Mandatory/Recommended Encoding 

Table 1 shows a list of characters that are not allowed within the URL syntax: these native 

characters must therefore be replaced by hex-encoding. Table 2 shows additional characters 

where it is recommended that characters be replaced by hex-encoding. The distinction between 

Tables 1 and 2 is between practical experience with current web browsers and the more formal 

specification of URL syntax. The web is still a relatively new environment and both the formal 

10

specifications and web browser implementations are something of a moving target. It can say 

with certainty that the characters in Table 1 must be hex encoded. It cannot say with certainty 

that the characters in Table 2 must or must not be hex encoded, only that the formal 

specifications recommend it but no recent set of browsers require it. 

The tables are formatted to show the given character, the encoding required by the DOI system 

for input, the encoding required for use of a DOI within a URL, and finally what is stored. The 

| symbol is used to show a series of acceptable alternatives, e.g., the fact that # can be entered 

into a web form as either # or %23 is shown as # | %23. Note that all the given characters must 

be hex encoded within URLs but that only %, because of its use as marking the start of a hex 

encoding, must be hex encoded in the various DOI forms. 

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Table 1 – Mandatory Encoding 

Character Input URLs DOI Database 

Web Form Batch 

# # | %23 # | %23 %23 # 

% %25 %25 %25 % 

SP SP | %20 SP | %20 %20 SP 

" " | %22 " | %22 " | %22 " 

Table 2 – Recommended Encoding 

Character Input URLs DOI Database 

Web Form Batch 

< > | %62 > | %62 %62 > 

{ { | %123 { | %123 %123 { 

} } | %125 } | %125 %125 } 

^ ^ | %94 ^ | %94 %94 ^ 

[ [ | %91 [ | %91 %91 [ 

] ] | %93 ] | %93 %93 ] 

` ` | %96 ` | %96 %96 ` 

| "|" | %124 "|"| %124 %124 | 

\ \ | %92 \ | %92 %92 \ 

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Digital Object Identifier - DOIs

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