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69-696: A digital object identifier ( DOI ) is a persistent identifier or handle used to uniquely identify various objects, standardized by the International Organization for Standardization (ISO). DOIs are an implementation of the Handle System ; they also fit within the URI system ( Uniform Resource Identifier ). They are widely used to identify academic, professional, and government information, such as journal articles, research reports, data sets, and official publications . A DOI aims to resolve to its target,

138-542: A first-class entity , rather than the specific place where the object is located at a certain time. It implements the Uniform Resource Identifier ( Uniform Resource Name ) concept and adds to it a data model and social infrastructure. A DOI name also differs from standard identifier registries such as the ISBN , ISRC , etc. The purpose of an identifier registry is to manage a given collection of identifiers, whereas

207-448: A DOI name is a handle, and so has a set of values assigned to it and may be thought of as a record that consists of a group of fields. Each handle value must have a data type specified in its <type> field, which defines the syntax and semantics of its data. While a DOI persistently and uniquely identifies the object to which it is assigned, DOI resolution may not be persistent, due to technical and administrative issues. To resolve

276-536: A DOI name, it may be input to a DOI resolver, such as doi.org . Another approach, which avoids typing or copying and pasting into a resolver is to include the DOI in a document as a URL which uses the resolver as an HTTP proxy, such as https://doi.org/ (preferred) or http://dx.doi.org/ , both of which support HTTPS. For example, the DOI 10.1000/182 can be included in a reference or hyperlink as https://doi.org/10.1000/182 . This approach allows users to click on

345-844: A URL resolves. A simple PURL works by responding to an HTTP GET request by returning a response of type 302 (equivalent to the HTTP status code 302, meaning "Found"). The response contains an HTTP "Location" header, the value of which is a URL that the client should subsequently retrieve via a new HTTP GET request. PURLs implement one form of persistent identifier for virtual resources. Other persistent identifier schemes include Digital Object Identifiers (DOIs), Life Sciences Identifiers (LSIDs) and INFO URIs . All persistent identification schemes provide unique identifiers for (possibly changing) virtual resources, but not all schemes provide curation opportunities. Curation of virtual resources has been defined as, "the active involvement of information professionals in

414-580: A URN. Persistent identifier The term "persistent identifier" is usually used in the context of digital objects that are accessible over the Internet. Typically, such an identifier is not only persistent but actionable: you can plug it into a web browser and be taken to the identified source. Of course, the issue of persistent identification predates the Internet. Over centuries, writers and scholars developed standards for citation of paper-based documents so that readers could reliably and efficiently find

483-497: A fragment identifier is already present in a target URL, any fragment in the original URL should be abandoned. Bos' suggestion failed to navigate the IETF standards track and expired without further work. Dubost et al. resurrected Bos' suggestions in a W3C Note (not a standard, but guidance in the absence of a standard). Makers of Web clients such as browsers have "generally" failed to follow Bos' guidance. Starting with PURLz 1.0 series,

552-401: A managed registry (providing both social and technical infrastructure). It does not assume any specific business model for the provision of identifiers or services and enables other existing services to link to it in defined ways. Several approaches for making identifiers persistent have been proposed. The comparison of persistent identifier approaches is difficult because they are not all doing

621-467: A manner identical to a 301 or 302 redirection, with the difference that a PURL server will handle the redirection internally for greater efficiency. This efficiency is useful when many redirections are possible; since some Web browsers will stop following redirections once a set limit is encountered (in an attempt to avoid loops). A PURL of type "200" is an "Active PURL", in which the PURL actively participates in

690-457: A network failure prevented it or because it did not exist. PURLs are themselves valid URLs, so their components must map to the URL specification. The scheme part tells a computer program, such as a Web browser, which protocol to use when resolving the address. The scheme used for PURLs is generally HTTP. The host part tells which PURL server to connect to. The next part, the PURL domain, is analogous to

759-543: A non-profit organization created in 1997, is the governance body of the DOI system. It safeguards all intellectual property rights relating to the DOI system, manages common operational features, and supports the development and promotion of the DOI system. The IDF ensures that any improvements made to the DOI system (including creation, maintenance, registration, resolution and policymaking of DOI names) are available to any DOI registrant. It also prevents third parties from imposing additional licensing requirements beyond those of

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828-464: A pointer to more specific information within a resource and are designated as following a # separator in URIs. Partial redirection in the presence of a fragment identifier is problematic because two conflicting interpretations are possible. If a fragment is attached to a PURL of type "partial", it is unclear whether a PURL service should assume that the fragment has meaning on the target URL, or discard it in

897-588: A registered PURL. If so, a redirection occurs with the remainder of the requested URL appended to the target URL. For example, consider a PURL with a URL of http//purl.org/some/path/ with a target URL of http://example.com/another/path/. An attempt to perform an HTTP GET operation on the URL http//purl.org/some/path/and/some/more/data would result in a partial redirection to http://example.com/another/path/and/some/more/data. The concept of partial redirection allows hierarchies of Web-based resources to be addressed via PURLs without each resource requiring its own PURL. One PURL

966-408: A resource path in a URL. The domain is a hierarchical information space that separates PURLs and allows for PURLs to have different maintainers. One or more designated maintainers may administer each PURL domain. Finally, the PURL name is the name of the PURL itself. The domain and name together constitute the PURL's "id". Both permalink and PURL are used as permanent/persistent URL and redirect to

1035-485: A source that a writer mentioned in a footnote or bibliography. After the Internet started to become an important source of information in the 1990s, the issue of citation standards became important in the online world as well. Studies have shown that within a few years of being cited, a significant percentage of web addresses go "dead", a process often called link rot . Using a persistent identifier can slow or stop this process. An important aspect of persistent identifiers

1104-403: A suitable replacement has not been identified. PURLs of type "clone" are used solely during PURL administration as a convenient method of copying an existing PURL record into a new PURL. The PURL service includes a concept known as partial redirection. If a request does not match a PURL exactly, the requested URL is checked to determine if some contiguous front portion of the PURL string matches

1173-419: A transaction, etc. The names can refer to objects at varying levels of detail: thus DOI names can identify a journal, an individual issue of a journal, an individual article in the journal, or a single table in that article. The choice of level of detail is left to the assigner, but in the DOI system it must be declared as part of the metadata that is associated with a DOI name, using a data dictionary based on

1242-514: Is a stub . You can help Misplaced Pages by expanding it . PURL A persistent uniform resource locator ( PURL ) is a uniform resource locator (URL) (i.e., location-based uniform resource identifier or URI) that is used to redirect to the location of the requested web resource . PURLs redirect HTTP clients using HTTP status codes . Originally, PURLs were recognizable for being hosted at purl.org or other hostnames containing purl . Early on many of those other hosts used descendants of

1311-450: Is a type of Handle System handle, which takes the form of a character string divided into two parts, a prefix and a suffix, separated by a slash. The prefix identifies the registrant of the identifier and the suffix is chosen by the registrant and identifies the specific object associated with that DOI. Most legal Unicode characters are allowed in these strings, which are interpreted in a case-insensitive manner. The prefix usually takes

1380-554: Is about the OCLC's PURL system, proposed and implemented by OCLC (the Online Computer Library Center). The PURL concept was developed by Stuart Weibel and Erik Jul at OCLC in 1995. The PURL system was implemented using a forked pre-1.0 release of Apache HTTP Server . The software was modernized and extended in 2007 by Zepheira under contract to OCLC and the official website moved to http://purlz.org (the 'Z' came from

1449-666: Is maintained by the International DOI Foundation. The IDF is recognized as one of the federated registrars for the Handle System by the DONA Foundation (of which the IDF is a board member), and is responsible for assigning Handle System prefixes under the top-level 10 prefix. Registration agencies generally charge a fee to assign a new DOI name; parts of these fees are used to support the IDF. The DOI system overall, through

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1518-461: Is shown with a DOI name that leads to an Excel file of data underlying the tables and graphs. Further development of such services is planned. Other registries include Crossref and the multilingual European DOI Registration Agency (mEDRA) . Since 2015, RFCs can be referenced as doi:10.17487/rfc ... . The IDF designed the DOI system to provide a form of persistent identification , in which each DOI name permanently and unambiguously identifies

1587-455: Is sufficient to serve as a top-level node for a hierarchy on a single target server. The new PURL service uses the type "partial" to denote a PURL that performs partial redirection. Partial redirections at the level of a URL path do not violate common interpretations of the HTTP 1.1 specification. However, the handling of URL fragments across redirections has not been standardized and a consensus has not yet emerged. Fragment identifiers indicate

1656-552: Is supported on newly created software, separate from all previous implementations. The transfer re-enabled the ability to manage PURL definitions that had been disabled in the OCLC-hosted service for several months. The service hosted on Internet Archive servers supports access via purl.org , purl.net , purl.info , and purl.com . OCLC now redirects DNS requests for purl.oclc.org to purl.org . The PURL concept allows for generalized URL curation of HTTP URIs on

1725-415: Is that "persistence is purely a matter of service". That means that persistent identifiers are only persistent to the degree that someone commits to resolving them for users. No identifier can be inherently persistent, however many persistent identifiers are created within institutionally administered systems with the aim to maximise longevity. However, some regular URLs (i.e. web addresses), maintained by

1794-451: Is to inform the Web client and end user that the PURL should always be used to address the requested resource, not the final URI resolved. This is to allow continued resolution of the resource if the PURL changes. Some operators prefer to use PURLs of type 301 (indicating that the final URI should be addressed in future requests). A PURL of type "chain" allows a PURL to redirect to another PURL in

1863-554: Is to use one of a number of add-ons and plug-ins for browsers , thereby avoiding the conversion of the DOIs to URLs, which depend on domain names and may be subject to change, while still allowing the DOI to be treated as a normal hyperlink. A disadvantage of this approach for publishers is that, at least at present, most users will be encountering the DOIs in a browser, mail reader , or other software which does not have one of these plug-ins installed. The International DOI Foundation ( IDF ),

1932-469: Is used to direct a Web client to a resource that provides additional information regarding the resource they requested, without returning the resource itself. This subtlety is useful when the HTTP URI requested is used as an identifier for a physical or conceptual object that cannot be represented as an information resource. PURLs of type 303 are used most often to redirect to metadata in a serialization format of

2001-523: The Apache License, Version 2.0 . PURLz 2.0 was released in Beta testing in 2010 but the release was never finalized. The Callimachus Project implemented PURLs as of its 1.0 release in 2012. The oldest PURL HTTP resolver was operated by OCLC from 1995 to September 2016 and was reached as purl.oclc.org as well as purl.org , purl.net , and purl.com . Other notable PURL resolvers include

2070-621: The Resource Description Framework (RDF) and have relevance for Semantic Web and linked data content. This use of the 303 HTTP status code is conformant with the http-range-14 finding of the Technical Architecture Group of the World Wide Web Consortium . A PURL of type "307" informs a user that the resource temporarily resides at a different URL from the norm. PURLs of types 404 and 410 note that

2139-513: The World Wide Web . PURLs allow third party control over both URL resolution and resource metadata provision. A URL is simply an address of a resource on the World Wide Web. A Persistent URL is an address on the World Wide Web that causes a redirection to another Web resource. If a Web resource changes location (and hence URL), a PURL pointing to it can be updated. A user of a PURL always uses

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2208-488: The indecs Content Model . The official DOI Handbook explicitly states that DOIs should be displayed on screens and in print in the format doi:10.1000/182 . Contrary to the DOI Handbook , Crossref , a major DOI registration agency, recommends displaying a URL (for example, https://doi.org/10.1000/182 ) instead of the officially specified format. This URL is persistent (there is a contract that ensures persistence in

2277-479: The DOI System. It requires an additional layer of administration for defining DOI as a URN namespace (the string urn:doi:10.1000/1 rather than the simpler doi:10.1000/1 ) and an additional step of unnecessary redirection to access the resolution service, already achieved through either http proxy or native resolution. If RDS mechanisms supporting URN specifications become widely available, DOI will be registered as

2346-413: The DOI as a normal hyperlink . Indeed, as previously mentioned, this is how Crossref recommends that DOIs always be represented (preferring HTTPS over HTTP), so that if they are cut-and-pasted into other documents, emails, etc., they will be actionable. Other DOI resolvers and HTTP Proxies include the Handle System and PANGAEA . At the beginning of the year 2016, a new class of alternative DOI resolvers

2415-409: The DOI system associates metadata with objects. A small kernel of common metadata is shared by all DOI names and can be optionally extended with other relevant data, which may be public or restricted. Registrants may update the metadata for their DOI names at any time, such as when publication information changes or when an object moves to a different URL. The International DOI Foundation (IDF) oversees

2484-436: The DOI system have deliberately not registered a DOI namespace for URNs , stating that: URN architecture assumes a DNS-based Resolution Discovery Service (RDS) to find the service appropriate to the given URN scheme. However no such widely deployed RDS schemes currently exist.... DOI is not registered as a URN namespace, despite fulfilling all the functional requirements, since URN registration appears to offer no advantage to

2553-456: The DOI system. DOI name-resolution may be used with OpenURL to select the most appropriate among multiple locations for a given object, according to the location of the user making the request. However, despite this ability, the DOI system has drawn criticism from librarians for directing users to non-free copies of documents, that would have been available for no additional fee from alternative locations. The indecs Content Model as used within

2622-627: The DOI useless. The developer and administrator of the DOI system is the International DOI Foundation (IDF), which introduced it in 2000. Organizations that meet the contractual obligations of the DOI system and are willing to pay to become a member of the system can assign DOIs. The DOI system is implemented through a federation of registration agencies coordinated by the IDF. By late April 2011 more than 50 million DOI names had been assigned by some 4,000 organizations, and by April 2013 this number had grown to 85 million DOI names assigned through 9,500 organizations. Fake registries have even appeared. A DOI

2691-495: The IDF on users of the DOI system. The IDF is controlled by a Board elected by the members of the Foundation, with an appointed Managing Agent who is responsible for co-ordinating and planning its activities. Membership is open to all organizations with an interest in electronic publishing and related enabling technologies. The IDF holds annual open meetings on the topics of DOI and related issues. Registration agencies, appointed by

2760-595: The IDF, operates on a not-for-profit cost recovery basis. The DOI system is an international standard developed by the International Organization for Standardization in its technical committee on identification and description, TC46/SC9. The Draft International Standard ISO/DIS 26324, Information and documentation – Digital Object Identifier System met the ISO requirements for approval. The relevant ISO Working Group later submitted an edited version to ISO for distribution as an FDIS (Final Draft International Standard) ballot, which

2829-472: The IDF, provide services to DOI registrants: they allocate DOI prefixes, register DOI names, and provide the necessary infrastructure to allow registrants to declare and maintain metadata and state data. Registration agencies are also expected to actively promote the widespread adoption of the DOI system, to cooperate with the IDF in the development of the DOI system as a whole, and to provide services on behalf of their specific user community. A list of current RAs

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2898-609: The US Government Printing Office ( http://purl.fdlp.gov ), which is operated for the Federal Depository Library Program and has been in operation since 1997. The PURL concept is used in the w3id.org , that may replace the old PURL-services and PURL-technologies. On 27 September 2016 OCLC announced a cooperation with Internet Archive resulting in the transfer of the resolver service and its administration interface to Internet Archive. The service

2967-633: The Zepheira name and was used to differentiate the PURL open-source software site from the PURL resolver operated by OCLC). PURL version numbers may be considered confusing. OCLC released versions 1 and 2 of the Apache-based source tree, initially in 1999 under the OCLC Research Public License 1.0 License and later under the OCLC Research Public License 2.0 License ( http://opensource.org/licenses/oclc2 ). Zepheira released PURLz 1.0 in 2007 under

3036-458: The characters 1000 in the prefix identify the registrant; in this case the registrant is the International DOI Foundation itself. 182 is the suffix, or item ID, identifying a single object (in this case, the latest version of the DOI Handbook ). DOI names can identify creative works (such as texts, images, audio or video items, and software) in both electronic and physical forms, performances , and abstract works such as licenses, parties to

3105-402: The context of an HTTP conversation but do not apply to the process of HTTP redirection. Three additional types of PURLs ("chain", "partial' and "clone") are given mnemonic names related to their functions. Most PURLs are so-called "simple PURLs", which provide a redirection to the desired resource. The HTTP status code, and hence of the PURL type, of a simple PURL is 302. The intent of a 302 PURL

3174-510: The creation or aggregation of the metadata returned. An Active PURL includes some arbitrary computation to produce its output. Active PURLs have been implemented in PURLz 2.0 and The Callimachus Project . They may be used to gather runtime status reports, perform distributed queries or any other type of data collection where a persistent identifier is desired. Active PURLs act similar to a stored procedure in relational databases. A PURL of type "303"

3243-410: The document, whereas its location and other metadata may change. Referring to an online document by its DOI should provide a more stable link than directly using its URL. But if its URL changes, the publisher must update the metadata for the DOI to maintain the link to the URL. It is the publisher's responsibility to update the DOI database. If they fail to do so, the DOI resolves to a dead link , leaving

3312-400: The doi.org domain,) so it is a PURL —providing the location of an name resolver which will redirect HTTP requests to the correct online location of the linked item. The Crossref recommendation is primarily based on the assumption that the DOI is being displayed without being hyperlinked to its appropriate URL—the argument being that without the hyperlink it is not as easy to copy-and-paste

3381-453: The form 10.NNNN , where NNNN is a number greater than or equal to 1000 , whose limit depends only on the total number of registrants. The prefix may be further subdivided with periods, like 10.NNNN.N . For example, in the DOI name 10.1000/182 , the prefix is 10.1000 and the suffix is 182 . The "10" part of the prefix distinguishes the handle as part of the DOI namespace, as opposed to some other Handle System namespace, and

3450-557: The full URL to actually bring up the page for the DOI, thus the entire URL should be displayed, allowing people viewing the page containing the DOI to copy-and-paste the URL, by hand, into a new window/tab in their browser in order to go to the appropriate page for the document the DOI represents. Major content of the DOI system currently includes: In the Organisation for Economic Co-operation and Development 's publication service OECD iLibrary , each table or graph in an OECD publication

3519-443: The functionality of a registry-controlled scheme and will usually lack accompanying metadata in a controlled scheme. The DOI system does not have this approach and should not be compared directly to such identifier schemes. Various applications using such enabling technologies with added features have been devised that meet some of the features offered by the DOI system for specific sectors (e.g., ARK ). A DOI name does not depend on

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3588-405: The information object to which the DOI refers. This is achieved by binding the DOI to metadata about the object, such as a URL where the object is located. Thus, by being actionable and interoperable , a DOI differs from ISBNs or ISRCs which are identifiers only. The DOI system uses the indecs Content Model to represent metadata . The DOI for a document remains fixed over the lifetime of

3657-537: The integration of these technologies and operation of the system through a technical and social infrastructure. The social infrastructure of a federation of independent registration agencies offering DOI services was modelled on existing successful federated deployments of identifiers such as GS1 and ISBN . A DOI name differs from commonly used Internet pointers to material, such as the Uniform Resource Locator (URL), in that it identifies an object itself as

3726-422: The location of the requested web resource . Roughly speaking, they are the same. Their differences are about domain name and time scale : The most common types of PURLs are named to coincide with the HTTP response code that they return. Not all HTTP response codes have equivalent PURL types and not all PURL servers implement all PURL types. Some HTTP response codes (e.g. 401, Unauthorized) have clear meanings in

3795-473: The management, including the preservation, of digital data for future use." PURLs have been criticized for their need to resolve a URL, thus tying a PURL to a network location. Network locations have several vulnerabilities, such as Domain Name System registrations and host dependencies. A failure to resolve a PURL could lead to an ambiguous state: It would not be clear whether the PURL failed to resolve because

3864-430: The object to which it is associated (although when the publisher of a journal changes, sometimes all the DOIs will be changed, with the old DOIs no longer working). It also associates metadata with objects, allowing it to provide users with relevant pieces of information about the objects and their relationships. Included as part of this metadata are network actions that allow DOI names to be resolved to web locations where

3933-411: The object's location and, in this way, is similar to a Uniform Resource Name (URN) or PURL but differs from an ordinary URL. URLs are often used as substitute identifiers for documents on the Internet although the same document at two different locations has two URLs. By contrast, persistent identifiers such as DOI names identify objects as first class entities: two instances of the same object would have

4002-454: The objects they describe can be found. To achieve its goals, the DOI system combines the Handle System and the indecs Content Model with a social infrastructure. The Handle System ensures that the DOI name for an object is not based on any changeable attributes of the object such as its physical location or ownership, that the attributes of the object are encoded in its metadata rather than in its DOI name, and that no two objects are assigned

4071-475: The original OCLC PURL system software. Eventually, however, the PURL concept came to be generic and was used to designate any redirection service (named PURL resolver ) that: PURLs are used to curate the URL resolution process, thus solving the problem of transitory URIs in location-based URI schemes like HTTP. Technically the string resolution on PURL is like SEF URL resolution . The remainder of this article

4140-414: The presumption that a resource with a changed location may have also changed content, thus invalidating fragments defined earlier. Bos suggested that fragments should be retained and passed through to target URLs during HTTP redirections resulting in 300 (Multiple Choice), 301 (Moved Permanently), 302 (Found) or 303 (See Other) responses unless a designated target URL already includes a fragment identifier. If

4209-466: The primary purpose of the DOI system is to make a collection of identifiers actionable and interoperable, where that collection can include identifiers from many other controlled collections. The DOI system offers persistent, semantically interoperable resolution to related current data and is best suited to material that will be used in services outside the direct control of the issuing assigner (e.g., public citation or managing content of value). It uses

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4278-455: The requested resource could not be found and suggests some information for why that was so. Support for the HTTP 307 (Temporary Redirect), 404 (Not Found) and 410 (Gone) response codes are provided for completeness. PURLs of types "404" and "410" are provided to assist administrators in marking PURLs that require repair. PURLs of these types allow for more efficient indications of resource identification failure when target resources have moved and

4347-411: The same DOI name. DOI name resolution is provided through the Handle System , developed by Corporation for National Research Initiatives , and is freely available to any user encountering a DOI name. Resolution redirects the user from a DOI name to one or more pieces of typed data: URLs representing instances of the object, services such as e-mail, or one or more items of metadata. To the Handle System,

4416-537: The same DOI name. Because DOI names are short character strings, they are human-readable, may be copied and pasted as text, and fit into the URI specification. The DOI name-resolution mechanism acts behind the scenes, so that users communicate with it in the same way as with any other web service; it is built on open architectures , incorporates trust mechanisms , and is engineered to operate reliably and flexibly so that it can be adapted to changing demands and new applications of

4485-471: The same Web address, even though the resource in question may have moved. PURLs may be used by publishers to manage their own information space or by Web users to manage theirs; a PURL service is independent of the publisher of information. PURL services thus allow the management of hyperlink integrity. Hyperlink integrity is a design trade-off of the World Wide Web, but may be partially restored by allowing resource users or third parties to influence where and how

4554-431: The same thing. Imprecisely referring to a set of schemes as "identifiers" does not mean that they can be compared easily. Other "identifier systems" may be enabling technologies with low barriers to entry, providing an easy to use labeling mechanism that allows anyone to set up a new instance (examples include Persistent Uniform Resource Locator (PURL), URLs, Globally Unique Identifiers (GUIDs), etc.), but may lack some of

4623-530: The website owner, are intended to be long-lasting; these are often called permalinks . People and organisations: Publications: Uniform Resource Identifiers : Combined persistent identifier and archiving functionality is provided by services such as the Internet Archive perma.cc , archive.today , and WebCite such that anyone can archive a web page to prevent link rot of a URL. This article relating to library science or information science

4692-506: Was approved by 100% of those voting in a ballot closing on 15 November 2010. The final standard was published on 23 April 2012. DOI is a registered URI under the info URI scheme specified by IETF RFC   4452 . info:doi/ is the infoURI Namespace of Digital Object Identifiers. The DOI syntax is a NISO standard, first standardized in 2000, ANSI/NISO Z39.84-2005 Syntax for the Digital Object Identifier. The maintainers of

4761-609: Was started by http://doai.io. This service is unusual in that it tries to find a non-paywalled (often author archived ) version of a title and redirects the user to that instead of the publisher's version . Since then, other open-access favoring DOI resolvers have been created, notably https://oadoi.org/ in October 2016 (later Unpaywall ). While traditional DOI resolvers solely rely on the Handle System, alternative DOI resolvers first consult open access resources such as BASE (Bielefeld Academic Search Engine). An alternative to HTTP proxies

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