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Last modified: January 15, 2004
Digital Object Identifier (DOI) System


"The Digital Object Identifier (DOI) is a system for identifying and exchanging intellectual property in the digital environment. It provides a framework for managing intellectual content, for linking customers with content suppliers, for facilitating electronic commerce, and enabling automated copyright management for all types of media. Using DOIs makes managing intellectual property in a networked environment much easier and more convenient, and allows the construction of automated services and transactions for e-commerce... The simplest DOIs (such as those in the earliest implementations of DOI) are essentially redirection from a persistent name (the DOI) to a changeable URL. The information associated with the DOI in the DOI system is therefore simply the URL and relevant administrative information for managing the DOI... DOIs can be applied to any piece of intellectual property (creation), but not to entities such as people and agreements. The DOI concept could be applied to any such entity but our initial applications were confined to describing the intellectual property rather than its users or uses... DOI uses the Handle system for resolution of the identifier, and the indecs framework (as implemented in ISO MPEG-21 Part 6) for metadata description, each of which also define their scope as equivalent to that of URI... Formally, DOI scope is defined in terms of a data model, the model underlying the indecs/MPEG-21 RDD work: a DOI can be assigned to any entity which is a Resource within the indecs (MPEG-21 RDD) model of e-commerce. This means the type of entity must be described in terms of attributes in the dictionary (e.g., media, mode, content, subject), and become an entry in the indecs Data Dictionary (MPEG RDD) used by the DOI system. The practical outcome of this is important and provides a pragmatic functional specification: a DOI can identify any Resource, but the DOI System requires that the Resource is defined (technically and hence precisely) in terms of agreed public (RDD) attributes..."[ home page 2003-03-15 and FAQ]


The DOI System makes use of XML (Extensible Markup Language), and XML is entirely compatible with DOI. The expression of DOI metadata in XML is recommended, both for kernel metadata and for DOI Application Profile metadata extended from the kernel. The DOI namespace (data dictionary) based on indecs is being developed in a basic semantic form, with XML expressions. XML is commonly used for metadata transport and messaging.

It seems likely that the relationship between DOI and XML will grow over time. One obvious link is in developing DOI Application Profiles for the various emerging XML schemas for industry-specific uses, such as NewsML: when such a scheme has been developed, DOIs provide an obvious way of adding functionality (persistent identification, interoperable metadata mappings, multiple resolution framework, etc.) to that schema for practical uses.

The linking of entities in XML is very different to the linking of entities with DOIs, as the two serve different, complementary purposes. XML entity resolution is concerned with the construction of an XML document or message; it exists to support the assembly of XML documents from components. DOI resolution, on the other hand, deals with information about an identified entity and linkage of intellectual property entities and information about those entities. DOIs may of course be used to identify entities which are "marked up" in an XML schema; but not every tagged entity in an XML schema may merit a DOI, unless there is a need for separate management of that entity (functional granularity).

Several languages have been constructed using XML that support functions complementary to DOI: e.g., XLink is a language that allows XML elements to be made into links, which specify relationship types and behaviour characteristics between sets of resources; the Resource Description Framework is another language that can be expressed in XML and allows properties of an identified resource to be described. Although neither of these technologies are yet mainstream, they have similar characteristics to, and can be used with, DOIs. The IDF is actively pursuing such usages and monitors XML developments closely. [from the DOI FAQ document]

DOI as relevant to rights transactions (DRM)

"Fundamental to rights transactions are the concepts of unique identification and appropriate structured metadata. DOI implements the indecs approach, which has at its heart the concept of rights management. IDF is working with others to introduce the concepts of DOI and indecs into digital rights management activities such as MPEG-21, OEBF, TV-Anytime, etc... The IDF, together with EDItEUR, is responsible for managing and further developing the output of indecs, and in a Consortium to build a Rights Data Dictionary - a common dictionary or vocabulary for intellectual property rights named to enable the exchange of key information between content industries and ecommerce trading of intellectual property rights. Work done by IDF in developing the DOI Namespace (a data dictionary for DOI use, based on indecs) was used as input to <indecs>rdd, now renamed Contecs:DD. This data dictionary has been accepted as the basis for the ISO MPEG-21 rights data dictionary." [from the FAQ]

"The adoption of <indecs> principles as the basis of MPEG-21's Rights Data Dictionary": - In November 2001, IFD announced that it was "a founding sponsor of the <indecs> consortium [formed] to develop a Rights Data Dictionary -- a common dictionary or vocabulary for intellectual property rights (Contecs:DD). The dictionary resulting from this activity was adopted as baseline technology for the ISO-MPEG-21 Rights Data Dictionary standard. The MPEG-21 Rights Data Dictionary, based on Contecs:DD principles, will provide a key part of the architecture required to deliver interoperability between develop a digital rights management (DRM) standard systems. In July 2002 the MPEG-21 Multimedia Description Schemes Subgroup completed the Committee Draft for MPEG-21 Part 6, Rights Data Dictionary (RDD)... IDF is now investigating effective ways for DOI Application Profiles to be built using the MPEG-21 RDD..."

See "MPEG Rights Expression Language" for details on MPEG-21 Part 6 and MPEG-21 Part 5: Rights Expression Language (REL).

Structure of a DOI

The DOI has two components, the prefix and the suffix, which together form the DOI. There is no limitation on the length of a DOI. A DOI may be assigned to any item of intellectual property, which must be precisely defined by means of structured metadata. The DOI itself remains persistent through ownership changes, and unaltered once assigned.

A prefix is assigned to an organization that wishes to register DOIs; any organization may choose to have multiple prefixes. Following the prefix (separated by a forward slash) is a suffix (unique to a given prefix) to identify the entity. The combination of a prefix for the Registrant and unique suffix provided by the Registrant avoids any necessity for the centralized allocation of DOI numbers.

An existing standard identification system number such as ISBN may be incorporated into a DOI, by using this as the suffix, if the registrant finds it convenient to do so (it is course recommended that precisely the same entity be identified by the two systems). DOI is not alone in being a system that can incorporate existing identifiers: for example, physical bar codes can be used to express ISBNs. [from the DOI System Overview]

The Cost of Using DOI

"At the outset of the DOI development, a very simple model was introduced whereby a prefix assignment is purchased for a one-off fee. A fee was introduced not to cover actual costs, but to recognize the fact that some charging for DOIs would be the intention... The disadvantage of using the direct $1000 route is that there is no metadata support and no social infrastructure support of the type, which can be given by a Registration Agency such as CrossRef..." [DOI Handbook, Chapter 13, Operating Procedures"]

The cost of assigning a depends upon the particular application. "Registration Agencies (RAs) are free to set fees independentl of the IDF [which] allows a range of pricing and business models using third party registration agencies... The current charge for a DOI prefix directly from the IDF is $1000. This one-off charge allows an unlimited number of DOIs to be constructed using that prefix, however DOIs allocated using prefixes purchased directly from IDF are registered without structured metadata: there is no metadata support and no social infrastructure support of the type which can be given by a Registration Agency such as CrossRef. There is currently no additional annual fee for maintenance of a prefix obtained in this way, though we reserve the right to vary this at a future date..." [from the FAQ document v2.7.0, February 2003]

Overview of the DOI System

"The DOI is more than just a way of naming things -- it is an integrated system. The DOI System is made up of a number of interacting components that depend on one another for their value. The whole is much greater than simply the sum of the parts... In this Handbook, we will view the DOI System as being made up of four primary components:

  • Enumeration: assigning a number (or name) to the intellectual property entity that the DOI identifies. It is more correct to talk about the DOI as an alphanumeric string, since a DOI may contain characters as well as numbers. However, we will use the term 'number' to apply to this string, to avoid unnecessary complexity.
  • Description: creating a description ('metadata') of the entity that has been identified with a DOI.
  • Resolution: making the identifier 'actionable' by providing information about what the DOI should resolve to, and the technology to deliver the services that this can provide to users.
  • Policies: the rules that govern the operation of the system.

[adapted from DOI Handbook Chapter 3, The components of the DOI system]

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