Reliable Access to Digital Objects

There are billions of digital objects in the Web. Many of them live only a day or two, but some need to be accessible for years to come. Permanent access to all kinds of scientific, cultural and other resources is vital for building knowledge and providing information services.

The PersID initiative provides persistent identifiers as well as a transparent policy and technical framework for using them in the Internet.

Give Things Names, Not Just Addresses

Web addresses such as Uniform Resource Locators (URLs) are an unreliable way of referring to digital objects. URLs are, after all, only addresses. Like people, digital contents move from one address to another, and the old address may be taken over by different contents. We all know that broken links are a significant nuisance. More subtly, a link may work but the target changes - the results of confusion may be dramatic. After long enough time, almost every URL will become useless.

More and more of what we see on the Web is an aggregation of resources from a number of sources. A researcher, referring in his article to research data, needs to be sure that the link to the data will be working long after it was made. In case of a broken link a human reader could think of alternative ways to find the missing object - but might not bother to make the effort. A computer will be out of luck.

The solution is giving digital objects persistent identifiers. They act as individual names for the objects. They help to find, identify and tell apart digital objects. They also make it easier to keep digital objects accessible on the long term, over changes of technology, organizations, and people, as they are independent of changes in publishing systems, transfer of ownership, and evolution of technology.

An identifier must be globally unique, and should also be actionable - that is, a persistent identifier should provide a persistent link to the resource identified.

The PersID initiative provides an independent, flexible and trustworthy system of identifying resources and making reliable links to them through implementation of an international standard system, the National Bibliography Number (NBN). It builds upon proven technologies and standards already in wide use, the IETF RFC3188. The initiative consists of diverse organizations that have a long-term responsibility for large amounts of publications, cultural materials and research data.

Using Uniform Resource Names (URN)

Persistent identifiers are not a new invention, but they are often not used in a durable and consistent manner. The identifier system chosen in the PersID initiative are the URNs, Uniform Resource Names. The URN system encompasses the traditional bibliographic identifiers such as ISBN and ISSN. URN system is flexible, standardized, and governed by a public body, Internet Engineering Task Force (IETF). The system was initially developed in the late 1990s. At the moment, the Internet standards that define the URN system are being revised to answer to requirements of the day.

Other persistent identifier systems exist, and can be used instead of or in parallel with URNs. PersID initiative is tailored towards organizations such as national libraries that have a long-term responsibility for preserving very large digital collections and they require a fully standardized and open persistent identifier solution to carry out this responsibility. This is why URN has been chosen. There are already millions of objects with URNs around, and the number is rising rapidly.

NBN - Flexibility and Control Combined

URNs can easily exploit any existing identifier scheme, such as ISBN numbers of books. Different schemes are simply embedded in the structure of a URN by assigning namespaces for them. Namespace registration gives an overall view of the identifier scheme and specifies how URNs in that particular namespace can be resolved.

NBN stands for National Bibliographic Number. National libraries administrate them. They may be assigned to a wide variety of digital objects - text, image, sound, video, data, etc. Other organizations may obtain a sub-namespace via their national library and assign identifiers independently, on condition that they must adhere to the national NBN policy. That way generating new identifiers can be integrated into local processes without jeopardizing the uniqueness of the identifiers.

Resolution Makes the Identifier Click

To give a document or other resource a persistent identifier is the first step but it is not enough. There must be an easy way to exploit the identifier and find the resource. A persistent identifier should also provide persistent linking.

The PersID initiative consists of a network of national URN resolvers, plus a meta resolver that is aware of all the national resolvers. Every resolver is provided with up-to-date data about URNs that are assigned to objects, and about the current location of those objects. Every organization assigning URNs will be responsible for updating data about its URNs.

The global resolver provides a unified user interface to the network of resolvers. There is a simple way to make a query about a URN. The global resolver delegates the query to the appropriate resolver which actually holds the current data about the URN and redirects the user to the resource. Optionally, the query may also return metadata about the object.

Global service will make it easy to integrate use of URNs into an information system. Wherever there is a URN, it can be resolved in the same way.

Persistence Needs Preservation

An object on the Web with an URN identifier should also stay on the Web. URNs make it easier to keep resources accessible over changes in technology. However, there are times when organizations disappear or are unable to fulfil their commitments. Huge amounts of useful material have been lost due to lack of resources, or responsibility. There must be a policy in place to prevent this from happening.

The participants of the PersID initiative have a long-term responsibility for preserving digital materials. Part of using URNs is to ensure that the objects with identifiers will be preserved and kept accessible, for example by the national libraries. The way this is done is part of the URN policies.

Building New Things on Solid Experience

The PersID initiative began as cooperation between a group of trusted European organizations that work with publications, cultural materials, as well as research data. We represent all stakeholder roles in the life cycle of persistent identification: document producers, identifier assigners and resolvers, URN and NBN authorities, and agencies that take care of long-term preservation. We believe that by backing technology and expertise with commitment and shared policies we will be able to provide an important and useful service. Only common, trusted governance can ensure sustainability over time, continued development of resolution services, and a sound business model.

What PersID Will Be

  • A global governance infrastructure to host services that make it easy to resolve names association, like NBN, to resources without link rot
  • A system based on open cooperation of research organizations, publishers, national libraries and others who benefit of persistent identifiers
  • Trustworthy, independent, public, flexible governance of URNs
  • Solid and secure infrastructure based on IETF standards and open source software
  • A network of up-to-date knowledge bases about URNs that offers
    • Easy use of URNs for managers of all kinds of digital contents
    • Easy use of URNs for users of digital contents

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