Namespace Registration for Digital Object Identifier (DOI)

Namespace ID:  DOI

Version:  1 

Date:  2023-03-14

Registrant:  

Name: Paul Jessop
E-mail: paul&countyanalytics.com
Affiliation: Technology Adviser, The DOI Foundation
Address: 
Web URL: https://doi.org/

Background:  

A Digital Object Identifier (DOI) name is a "digital identifier of an 
object" rather than an "identifier of a digital object". DOI names may 
be used for persistent and unique identification of objects of any type 
(digital, physical or abstract) and current applications of the DOI 
system include articles published in scholarly journals, scientific 
data sets and movie/TV production objects. 

The DOI system was initiated by The DOI Foundation in 1998. First 
applications were launched at 2000. As of this writing, about 275 
million DOI names have been assigned to objects managed by more than 
5000 organizations. These identifiers are resolved about 12 billion 
times per year (see https://www.doi.org/factsheets/DOIKeyFacts.html).  

DOI is an international standard under ISO 26324 and ISO has appointed 
The DOI Foundation as the registration authority. The DOI Foundation 
publishes the DOI Handbook and revises it from time to time - the 
current version was published in 2019-12-19. The Handbook is available 
at https://doi.org/10.1000/182 and gives information on implementation 
details that are not contained in the international standard, including 
the resolution system.

The Handle System, as specified in Digital Object Interface Resolution 
Protocol (DO-IRP, https://www.dona.net/specsandsoftware), has been 
designated as the DOI resolution system so that DOI names are Handles 
with additional characteristics specified in ISO 26324, in the DOI 
Handbook and by the registrant (the DOI Federation-affiliated agency 
assigning the DOI name). Handles assigned outside this framework are 
not required to have these characteristics.

It is possible to resolve DOIs using the native Handle resolution 
system, but this is typically accessed through an https proxy provided 
by the DOI Foundation with a global, scalable, load balancing caching 
architecture. This proxy is accessed by prepending "https://doi.org/" 
and optionally appending a query parameter. Details are in section 3.8 
of the DOI Handbook.

NOTE: The Handle System was originally specified in RFCs 3650-3652. 
These RFCs have been replaced in 2022 by Digital Object Identifier 
Resolution Protocol (see above). 

Purpose:

Enable presentation of DOI names as URNs.

Benefits:

When represented as URNs, DOI names can be easily located within full 
text even without the proxy address https://doi.org. 

When represented as URNs, DOI names can in the future become technology 
independent hyperlinks without the proxy address. 

The F-component (or URI fragment without a role in identification, as 
specified in the RFC 8141 URN syntax) can in the future be used with DOI 
names represented as URNs. This feature can be documented in the DOI 
Handbook.

URN Q- and R-components can in the future be used with DOI names in 
order to send requests to the target system or resolver, provided that 
the Handle.Net resolver is enhanced with support for these URN features. 

Character set:

According to ISO 26324, DOI names may incorporate any printable 
characters from ISO/IEC 10646, the ISO equivalent of the Unicode 
character set. DOI Registration Agencies are permitted to impose 
additional constraints on available characters and some, such as 
Crossref and DataCite, have done so.

Handle syntax imposes two constraints on the prefix — both slash and 
dot are "reserved characters", with the slash separating the prefix 
from the suffix and the dot used to extend sub prefixes. 

When DOI names are presented as HTTP URIs, they are prefixed by the DOI 
proxy resolver address https://doi.org (formerly http://dx.doi.org was 
used and while this still works, it is no longer recommended). The 
resolver address is not part of the identifier string. 

URI percent encoding (see RFC 3986, section 2.1) is required for 
characters in a DOI that are:

   o outside the ASCII printable character set, or
   o reserved in the URI syntax (see RFC 3986, section 2.2).

The same rule is applied in creating a URN.

Thus, # becomes %23 and the DOI 10.1000/456#789 becomes URI 
https://doi.org/10.1000/456%23789 and becomes URN 
urn:doi:10.1000/456%23789. 

Similarly, Unicode characters other than ASCII printable characters 
SHALL be percent encoded when a URN is created from a DOI.

Details of this process are contained in the DOI handbook.

NOTE: In practice, most DOIs use only printable ASCII characters. 

Syntax:

The DOI Namespace-Specific String (NSS) consists of three parts:

   o DOI prefix; 

   o a forward slash (/) as the delimiting character; and,

   o DOI suffix. 

In the original (2012) edition of ISO 26324, the DOI prefix is composed 
of a directory indicator "10" followed by a registrant code, which is 
a unique string assigned to a registrant. These two components are 
separated by a full stop (period).

The 2022 edition of ISO 26324 has amended the syntax of the prefix by 
removing the requirement for the directory indicator to be "10" and 
allow also DOI names without a registrant code.

DOI names created under the 2012 edition remain conformant under the 
2022 edition and all are compatible with this registration.

EXAMPLE 1

   10.1000 DOI prefix comprising a directory indicator "10" followed by 
   registrant code "1000".  

EXAMPLE 2

   15434 DOI prefix comprising a directory indicator of "15434" without 
   a registrant code.

The DOI suffix consists of a character string of any length chosen by 
the registrant. Each suffix is required to be unique within the space 
defined by the prefix element that precedes it. In some circumstances 
it can incorporate an identifier generated from or based on another 
system used by the registrant (e.g. ISAN, ISBN, ISRC, ISSN, ISNI). 
Information on incorporating other identifiers is contained in 
section 2.7 of the DOI Handbook.

EXAMPLE 3

   10.1000/182 DOI name with the DOI prefix "10.1000" and suffix "182". 

The following formal definition uses ABNF [RFC5234] and has been adapted 
from the one used in the EIDR URN namespace registration [RFC 7972].

URN-DOI = "urn:doi:" DOI-NSS
DOI-NSS = DOI-PREFIX "/" DOI-SUFFIX
DOI-PREFIX = 1*DOI-CHARS
DOI-SUFFIX = 1*DOI-CHARS
DOI-CHARS = %x20-7E

NOTE: The composition of the DOI prefix has as a matter of practice 
always been restricted to DIGIT / "." though there is no formal 
restriction in ISO 26324 that the registrant code must be numeric. 
The Handle System similarly is largely restricted to numeric codes in 
the prefix (though exceptionally the Library of Congress Handle prefix 
is not numeric). There is no plan to change this. 

Rules for lexical equivalence:

Since the DOI-NSS is case insensitive with respect to printable ASCII 
characters, parsers SHALL treat URN:DOIs accordingly and ignore such 
case when URN:DOI identifiers are compared.

URN F-, Q- and R-components SHALL be ignored in the comparison since 
they are not part of the NSS. 

ISO 26324 requires that when displayed on screen or in print, a DOI 
name should be preceded by a lowercase "doi:" unless the context 
clearly indicates that a DOI name is implied. The "doi:" label is not 
part of the DOI name and SHALL be ignored in comparison. 

Where comparison is made between different representations of a DOI 
name, the scheme and namespace of a URN representation, the "doi:" 
prefix of a display DOI name and the proxy resolver address SHALL be 
deleted and any percent encoding SHALL be removed before equivalence of 
two such DOI name representations is analyzed. 

EXAMPLE 4

   The following representations of a DOI name SHALL be regarded as 
   equivalent:

   urn:doi:10.1000/456%23789
   https://doi.org/10.1000/456%23789
   doi:10.1000/456#789
   10.1000/456#789

The EIDR URN namespace (documented in RFC 7972) is also made up of DOI 
names, assigned in this case by the Entertainment ID Registry, which 
is a DOI Registration Agency. When comparing a URN:EIDR and a URN:DOI 
for equivalence of the respective underlying DOI names, it is necessary 
to note that the syntax in RFC 7972 replaces the "/" between the DOI 
prefix and the DOI suffix with a ":" because the URN definition at the 
time RFC 7972 was published did not allow a "/" in a URN Namespace 
Specific String and the subsequent RFC 8141 does not retrospectively 
change this.

DOI assignment:

DOI assignment is managed by DOI Registration Agencies which act as 
registrants. Their roles and responsibilities are set out in chapter 8 
of the DOI Handbook:

https://www.doi.org/the-identifier/resources/handbook/8_registration_agencies

Rules for assignment of DOI names have been set in chapter 2.3 of the 
DOI Handbook:

https://www.doi.org/the-identifier/resources/handbook/2_numbering#2.3

The assignment of a DOI name requires that the registrant provide kernel 
metadata describing the object to which the DOI name is being assigned. 
The metadata must describe the object to the degree that is necessary 
to distinguish it as a separate entity within the DOI system.

The initial DOI kernel metadata is specified in Annex B of ISO 26324 and 
an extended schema is published by the DOI Foundation. 

Security and Privacy:

DOI names do not have any unmanaged privacy issues. Where the referent 
of a DOI name is a living person, the Registration Agency assigning the 
name is responsible for ensuring compliance with privacy and data 
protection requirements such as the General Data Protection Regulation 
of the EU and the California Consumer Privacy Act.

Due to the assignment by the DOI Foundation of prefixes and the 
assignment by DOI Registration Agencies of suffixes – all of which are 
aware of the need to manage the potential problem - it is unlikely to 
be possible to utilize Unicode confusable characters to create DOI 
names which may be confused by the users. 

Interoperability:  

DOI names do not have any known interoperability related problems. 
Because the DOI Foundation has designated the Handle System for the 
resolution of DOI names, they may be resolved by the Handle System proxy 
resolver at https://hdl.handle.net as well as by the DOI Foundation's 
own resolver network at https://doi.org. 

The 2022 edition of ISO 26324 enables existing Handle-based 
identification systems to be designated as part of the DOI system. In 
these circumstances, both the above proxy resolvers will continue to 
work (as well as native resolution by the Handle System in accordance 
with DO-IRP).

URNs in the URN:DOI namespace are interoperable with URNs in the 
URN:EIDR namespace (as defined in RFC 7972), in that the above 
resolution servers work with each and they share the same kernel 
metadata schema.

Resolution:  

URNs in the URN:DOI namespace SHALL be resolvable. Each resolution of a 
URN in the URN:DOI namespace SHALL return information about the referent 
of the DOI name represented.

DOI resolution is described in chapter 3 of the DOI Handbook:

https://www.doi.org/the-identifier/resources/handbook/3_resolution

To resolve a URN in the URN:DOI, the string to the right of "urn:doi:" 
may be resolved in the Handle System in accordance with the protocol 
defined in DO-IRP or be prepended with "https://doi.org/" and an https 
GET performed.

The DOI proxy resolver in practice already allows the resolution of a 
URN:DOI using NID "DOI". 

EXAMPLE	5

   https://doi.org/urn:doi:10.1000/182 resolves in the same way as 
   https:doi.org/10.1000/182 to the DOI Handbook.

Where the retrieved record includes a URL, the resolver will normally 
provide a redirect to that URL, which may be the referent itself, 
information about the referent or a "landing page" explaining how the 
referent may be accessed.

The DOI Handbook contains information on how to use the DOI proxy 
resolver with various query parameters to, for instance, prevent 
redirection or to bypass the cache. It also contains information about 
the use of multiple URLs and multiple resolution, allowing access to 
specific information stored in the Handle System about a referent.

Persistence:

DOI is a well-managed identifier system. 

Persistence of DOI information is a key aim of the DOI system, and is 
guaranteed by the DOI social infrastructure, policies and agreements. 
In the event of any Registration Agency ceasing to maintain DOI 
information, for any reason, the records will be transferred to another 
Registration Agency. This forms part of the legal agreement which each 
Registration Agency enters into with the DOI Foundation.

Additional documentation / information:  

See ISO 26324:2022 and the DOI Handbook. 

Revision Information:  

None