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What is the DOI?
The Digital Object Identifier (DOI) is a persistent identifier which may be used to cite and link to electronic documents such as text, image, audio, audiovisual, etc..
The DOI consists of a unique alpha-numeric character string divided in two parts: a prefix and a suffix.
The DOI is case insensitive (e.g. 10.1000/abc is the same as 10.1000/ABC) and the suffix must be unique within a prefix.
DOIs are actionable in the Internet. Users can resolve DOIs to the identified content and/or other resources related to that content. Unlike the URLs, DOIs are associated to documents and not to locations: if a document is moved to a different location, users are readdressed consequently to reach the correct page.

What is the DOI structure?
The DOI consists of a unique alpha-numeric character string divided in two parts: a prefix and a suffix.
For example:
10.1000 is the prefix
10 identifies the string as a DOI
1000 identifies the publisher
abc is the suffix (identifying the digital object)

The suffix can integrate other standard identifiers such as ISBN or ISSN. As a consequence, the DOI allows to mantain the standard identifiers already in use.
The suffix is assigned by the publisher (registrant).
The DOI is an "opaque string" or "dumb number" - nothing at all can or should be inferred from the number in respect of its use in the DOI System.

What is the relation between DOI and metadata?
Each DOI has associated with it some minimum set of metadata (the Kernel); and may have associated with it some additional metadata.
In order to provide services to both publishers and final users, mEDRA also needs to get some data about the documents and other content that publishers will register to the agency.

How can you supply metadata to mEDRA?
Publishers usually generate metadata during their production process and keep data for internal use. To publish a book, it's necessary to specify some metadata, as the name of the author, the title of the book, the date of publishing, etc. To publish an issue of a magazine or a journal, other metadata must be specified, as the number of the issue within the magazine, the list of articles contained in the issue, etc. To meet mEDRA's demand for metadata, publishers will have to feed the mEDRA DOI System with that kind of information. Thus, publishers will have to go through mEDRA metadata submitting process. After the process is completed, publishers, as well as other users, will be able to fully exploit mEDRA services.

What are the mEDRA metadata schemes?
mEDRA metadata are managed in XML, according to the ONIX-for-DOI-Registration Schemes. mEDRA uses ONIX metadata specification to provide a communication format for metadata related to the registration of DOIs.

Is it possible to update metadata?
Yes, every time you change your metadata you have to update them in mEDRA. This is particularly recommended when content's URL is changed.

Are DOIs ever deleted?
It is not possible to delete DOIs. If the content associated with the DOI no longer exists, mEDRA will provide a message to inform the user that the document is not available any longer.

DOI character set
DOIs string may incorporate any printable characters from the Universal Character Set (UCS-2), of ISO/IEC 10646, which is the character set defined by Unicode v2.0. The UCS-2 character set encompasses most characters used in every major language written today.

However the Handle System (the underlying resolution technology for DOI system) at its core uses UTF-8, so UTF-8 is the required coding. UTF-8 is a Unicode implementation and so in its pure form has no character set constraints at all: any character can be sent to, stored in, and retrieved from a handle server.

The IDF imposes no additional character set constraints.

Guidelines on DOI creation
Your DOI prefix will be assigned to your organization by mEDRA.

Mandatory guidelines

  • You have to assign the DOI suffix.
  • The suffix must be unique within the prefix and is case insensitive.
  • UTF-8 is the required coding.
  • If you use characters that have special meaning in URI Syntax, when you embed DOIs within URLs (for example to link the resolution system: you have to hexadecimal encode them. Find here the URI Syntax (
Recommended guidelines

  • Your organization should adopt a DOI assignment scheme, for example including existing internal identifiers in use within your organization.
  • The suffix should be as concise as possible because DOIs will be displayed online and in print and will be re-typed by end users.
  • It is recommended not to use the following characters in DOI suffix:

    ; / ? : @ & = + $ , * " %
    # < > ' } { | \ ^ [ ] ` SPACE

What do I have to do to get a DOI?
DOIs, similarly to ISBNs, are registered through Registration Agencies, and from that moment are permanently associated to digital objects.

What is a DOI registration agency?
Registration Agencies (RAs) are established to provide services on behalf of specific user communities. Choosing an appropriate RA will give you access to DOI services and implementations offered by the RA for that community.

How to cite a DOI
Example of citation using DOI in a HTML hyperlink.
DOIs may be used to create persistent citations to documents on the Web which are guaranteed to be always up to date.
  • A correct URL for citing a document with a DOI is:

  • The HTML code to obtain the above citation is:

  • A browser will show this code as:

What is resolution?
Resolution is the process of submitting an identifier [of an entity] to a network service and receiving in return one or more pieces of current information related to the identified entity. In the case of the Domain Name System (DNS), as an example, the resolution is from domain name, e.g.,, to a single IP address, e.g.,, which is then used to communicate with that Internet host. In the case of the DOI, using the Handle System as a reference implementation, the resolution is from a DOI, e.g., 10.1000/140, to one or more pieces of typed data: e.g. URLs representing instances of (manifestations of) the object, or services such as e-mail, or one or more items of metadata.

What is the International DOI Foundation?
DOI system is governed by the International DOI Foundation (IDF), a no-profit organisation.
The Foundation was created in 1998 and supports the development and promotion of the Digital Object Identifier system as a common infrastructure for content management. The Foundation is controlled by a Board elected by the members of the Foundation, with an appointed full-time Director who is responsible for co-ordinating and planning its activities. Through the elected Board, the activities of the Foundation are ultimately controlled by its members. Membership is open to all organizations with an interest in electronic publishing and related enabling technologies.