State of the Art Report (StoAR) Name: <StoAR_Persistent_Identifiers> Work Package: <Tools> Responsible: <Ahmed Rahali> Document history Date Version Status Author(s) Changes / comments <20.10.2004> 1 In progress ARA <13.01.2005> 1 First version ARA 1. Definition of the subject Persistent identification is regarded as an increasingly important aspect for strategies aimed to ensure effective management of digital information resources and their long-term access. The assignment of unique identifiers allows digital objects to be labelled or referenced in such a way that they can be reliably found over time in a dynamic distributed information environment. To date, various schemes have been suggested as a global approach to persistent identification, including the URN (Uniform Resource Name), the DOI (Digital Object Identifiers), the PURL (Persistent URL), the Handle System, the ARK (Archival Resource Key) and the XRI (eXtensible Resource Identifier). Each of these approaches came to birth as a result of progressive ongoing research and has succeeded, in varying degrees, to build communities around it. This document is aimed to provide an overview of current activity in the field of persistent identifiers and an understanding of the diverse persistent identification strategies being used and developed. The document is to serve as a reference for review and evaluation of all these various schemes and as a basis for recommendations of relevance to the eSciDoc project. 2. Keywords Persistent identifier, Persistent identification, Persistent link, Digital identifier, Persistence, Uniform Resource Name, Uniform Resource Identifier, Uniform Resource Locator, National Bibliography Number, Persistent URL, Handle, Digital Object Identifier, Archival Resource Key, eXtensible Resource Identifier, URI, URL, URN, NBN, PURL, DOI, ARK, infoURI, XRI. 1 Table of contents: Name: <StoAR_Persistent_Identifiers> ..............................................................................................1 Work Package: <Tools>.....................................................................................................................1 Responsible: <Ahmed Rahali> ..........................................................................................................1 Document history ..............................................................................................................................1 1. Definition of the subject ....................................................................................1 2. Keywords............................................................................................................1 3. Summary.............................................................................................................3 4. Third party activities:.........................................................................................4 5. State of the art....................................................................................................5 5.1 Introduction........................................................................................................6 5.1.1 Scope.............................................................................................................................6 5.1.2 Definitions ......................................................................................................................6 5.1.3 Background....................................................................................................................7 5.1.4 Aspects of persistent naming.........................................................................................8 5.2 Functional and Organisational Requirements.................................................8 5.3 Persistent Identification Systems.....................................................................9 5.3.1 Uniform Resource Identifiers (URIs)..............................................................................9 5.3.1.1 Uniform Resource Locators (URLs)...............................................................................9 5.3.1.2 Uniform Resource Names (URNs) ..............................................................................10 5.3.2 Persistent Uniform Resource Locators (PURLs) .........................................................12 5.3.3 The Handle System .....................................................................................................13 5.3.4 Digital Object Identifiers (DOIs) ...................................................................................17 5.3.5 Archival Resource Keys (ARKs) ..................................................................................19 5.3.6 Other Identifier Schemes .............................................................................................21 5.3.6.1 info Uniform Resource Identifier ( info URI)...................................................................21 5.3.6.2 eXtensible Resource Identifier (XRI) ...........................................................................22 5.3.7 Comparative Summary ................................................................................................22 5.4 Evaluation of Persistent Identification Schemes ..........................................23 5.4.1 Using the URN scheme ...............................................................................................23 5.4.2 Using PURLS...............................................................................................................23 5.4.3 Using Handles..............................................................................................................24 5.4.4 Using DOIs...................................................................................................................24 5.4.5 Using ARKs..................................................................................................................25 5.4.6 Summary......................................................................................................................25 5.5 Ensuring Persistent Access to Resources....................................................26 6. Relevance and conclusions for the project ...................................................27 7. Open questions................................................................................................28 8. References........................................................................................................29 2 3. Summary Persistent identifiers and an associated resolver service are an attempt to solve the common problem of broken links that occurs when resources on the web are moved to a new location or completely removed. Many Persistent Identification approaches have been proposed to tackle this problem by providing both consistent naming scheme for online resources and a resolver service to redirect users to the current location of a resource based on its persistent identifier. The main purpose of this report is to present the current state of technologies that assist the issue of Persistent Identification. Three aspects are taken into consideration: the semantics of the identifier itself, the issue of resolving the identifier to a resource or to further information on how to access the resource (metadata, another file, an html file etc.…) and, finally, recognising the importance of encouraging others to share responsibility for maintaining this access persistent. The schemes that are discussed and that constitute potential options are: the Uniform Resource Name (URN) of the Internet Engineering Task Force, the Persistent URL (PURL) of the Online Computer Library Center, the Handle System of the Corporation for National Research Initiatives, the Digital Object Identifier (DOI) of the International DOI Foundation and the Archival Resource Key (ARK) of the California Digital Library. The report sums up by defining dealing with the problem of persistence in two dimensions. First, it is supported by technical infrastructure manifested through an implementation based on one of the available systems that meet the requirements. Secondly, it needs to be governed by policies and guidelines that help promoting awareness for commitment to persistence and that encourage institutions and individuals to take responsibility towards guaranteeing the persistence of the resources they own. IMPORTANT: The report makes a couple of recommendations, but these are to be taken with caution as they are neither found on a thoroughly sufficient evaluation against a set of requirements nor based on profound and convincing practical tests. They are, rather, based on impressions and shallow experience gained while having to deal with this topic for the first time. 3 4. Third party activities: Organisation Identification Scheme Status of Activity The Internet Engineering Uniform Resource Names ( URN s) Available/ In Progress Task Force (The URN URN is a namespace of namespaces for URIs. This urn:NBN (RFC3188), in particular is Working Group) includes urn:ISBN (namespace for books), urn:ISBN being used by a number of national (namespace for journals) and urn:NBN (namespace for libraries across Europe. (IETF ) national bibliographic items). Online Computer Library Persistent Uniform Resource Locators ( PURL s) Available Center PURLs are simply URLs which use no new protocols, but A number of resolution servers have a set of tools that provide assistance to maintain URLs been put in place. By May 2004, over (OCLC ) with a commitment