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Uniform Resource Names URN

Persistent Identifiers for web resources.

The standard method of referencing resources on the internet is covered by Uniform Resource Locators URLs. These web addresses are unique, but there are not persistent. If a file or document is moved, i.e. into another directory, the reference becomes invalid. To identify a document regardless of its location, persistent, globally unique and standardized identifiers for digital content are necessary. Additionally, an unambigous indentification makes an article citable and distinguishable.

Different approaches have been made to solve the problem of persistent identifiers, one of them is the concept of Uniform Resource Names URN. Die Deutsche Bibliothek, in cooperation with international organizations such as CDNL “Persistent Identifiers” Working Group and CENL Working Group on Network Standards, has developed a stable address scheme. But the permanence of these addresses is only guaranteed if not applied locally. With the Epicur project, Die Deutsche Bibliothek, supported by the German Ministry of Education and Science, wants to create the foundations for a standard for managing and resolving URN addresses. The service offered by Die Deutsche Bibliothek currently resolves URNs in the namespace nbn:de.

Just as an ISB number for printed books the URN clearly identifies digital content of any kind and contains information about the referenced resource. A typical URN looks like: urn:nbn:de:1111-2003121811. Thereby, nbn:de identifies the namespace for a National Bibliography Number in Germany. It is followed by a four digit number that designates the publisher or the document server. The last part indicates the document itself by a unique number, containing a checksum.

Once registered in the database, the URL to a document with an URN is constantly updated in the database and is fetched, if it is requested by a user. A URN is build up hierarchically and is compliant with the RFC 2141 standard.

An URN may be resolved by resolving service, like nbn-resolving.de (for URNs in the nbn namespace), or directly from the browser, if an appropriate plugin is installed. For the Mozilla, Netscape or Firefox browser, a plugin is available from the website www.persistent-identifier.de that enables the user to directly enter the URN to a specific document. The plugin has been developed within the Epicur project and also relies on the nbn namespace.

Alternative solutions for persistent identifiers are the DOI Digital Object Identifiers (the DOI resolving service crossref has been established by a joint project of commercial scientific publishers) and the Persistent Uniform Resource Locators PURL promoted by the Online Computer Library Center in the USA.

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