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Independent Submission                                  H. Van de SompelRequest for Comments: 8574         Data Archiving and Networked ServicesCategory: Informational                                        M. NelsonISSN: 2070-1721                                  Old Dominion University                                                               G. Bilder                                                                Crossref                                                                J. Kunze                                              California Digital Library                                                               S. Warner                                                      Cornell University                                                              April 2019cite-as: A Link Relation to Convey a Preferred URI for ReferencingAbstract   A web resource is routinely referenced by means of the URI with which   it is directly accessed.  But cases exist where referencing a   resource by means of a different URI is preferred.  This   specification defines a link relation type that can be used to convey   such a preference.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This is a contribution to the RFC Series, independently of any other   RFC stream.  The RFC Editor has chosen to publish this document at   its discretion and makes no statement about its value for   implementation or deployment.  Documents approved for publication by   the RFC Editor are not candidates for any level of Internet Standard;   seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8574.Van de Sompel, et al.         Informational                     [Page 1]

RFC 8574            The "cite-as" Link Relation Type          April 2019Copyright Notice   Copyright (c) 2019 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .33.  Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . .33.1.  Persistent Identifiers  . . . . . . . . . . . . . . . . .33.2.  Version Identifiers . . . . . . . . . . . . . . . . . . .53.3.  Preferred Social Identifier . . . . . . . . . . . . . . .53.4.  Multi-resource Publications . . . . . . . . . . . . . . .6   4.  The "cite-as" Relation Type for Expressing a Preferred URI       for the Purpose of Referencing  . . . . . . . . . . . . . . .65.  Distinction with Other Relation Types . . . . . . . . . . . .85.1.  The "bookmark" Relation Type  . . . . . . . . . . . . . .95.2.  The "canonical" Relation Type . . . . . . . . . . . . . .96.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .106.1.  Persistent HTTP URI . . . . . . . . . . . . . . . . . . .116.2.  Version URIs  . . . . . . . . . . . . . . . . . . . . . .126.3.  Preferred Profile URI . . . . . . . . . . . . . . . . . .136.4.  Multi-resource Publication  . . . . . . . . . . . . . . .137.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .148.  Security Considerations . . . . . . . . . . . . . . . . . . .149.  References  . . . . . . . . . . . . . . . . . . . . . . . . .159.1.  Normative References  . . . . . . . . . . . . . . . . . .159.2.  Informative References  . . . . . . . . . . . . . . . . .15   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .17   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .17Van de Sompel, et al.         Informational                     [Page 2]

RFC 8574            The "cite-as" Link Relation Type          April 20191.  Introduction   A web resource is routinely referenced (e.g., linked or bookmarked)   by means of the URI with which it is directly accessed.  But cases   exist where referencing a resource by means of a different URI is   preferred, for example, because the latter URI is intended to be more   persistent over time.  Currently, there is no link relation type to   convey such an alternative referencing preference; this specification   addresses this deficit by introducing a link relation type intended   for that purpose.2.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.   This specification uses the terms "link context" and "link target" as   defined in [RFC8288].  These terms correspond with "Context IRI" and   "Target IRI", respectively, as used in [RFC5988].  Although defined   as IRIs (Internationalized Resource Identifiers), they are also URIs   in common scenarios.   Additionally, this specification uses the following terms:   o  "access URI": A URI at which a user agent accesses a web resource.   o  "reference URI": A URI, other than the access URI, that should      preferentially be used for referencing.   By interacting with the access URI, the user agent may discover typed   links.  For such links, the access URI is the link context.3.  Scenarios3.1.  Persistent Identifiers   Despite sound advice regarding the design of Cool URIs [CoolURIs],   link rot ("HTTP 404 Not Found") is a common phenomena when following   links on the Web.  Certain communities of practice (see examples   below) have introduced solutions to combat this problem.  These   solutions typically consist of:   o  Accepting the reality that the web location of a resource -- the      access URI -- may change over time.Van de Sompel, et al.         Informational                     [Page 3]

RFC 8574            The "cite-as" Link Relation Type          April 2019   o  Minting an additional URI for the resource -- the reference URI --      that is specifically intended to remain persistent over time.   o  Redirecting (typically with "HTTP 301 Moved Permanently", "HTTP      302 Found", or "HTTP 303 See Other") from the reference URI to the      access URI.   o  Committing, as a community of practice, to adjust that redirection      whenever the access URI changes over time.   This approach is, for example, used by:   o  Scholarly publishers that use DOIs (Digital Object Identifiers)      [DOIs] to identify articles and DOI URLs [DOI-URLs] as a means to      keep cross-publisher article-to-article links operational, even      when the journals in which the articles are published change hands      from one publisher to another, for example, as a result of an      acquisition.   o  Authors of controlled vocabularies that use PURLs (Persistent      Uniform Resource Locators) [PURLs] for vocabulary terms to ensure      that the URIs they assign to vocabulary terms remain stable even      if management of the vocabulary is transferred to a new custodian.   o  A variety of organizations (including libraries, archives, and      museums) that assign ARK (Archival Resource Key) URLs [ARK] to      information objects in order to support long-term access.   In order for the investments in infrastructure involved in these   approaches to pay off, and hence for links to effectively remain   operational as intended, it is crucial that a resource be referenced   by means of its reference URI.  However, the access URI is where a   user agent actually accesses the resource (e.g., it is the URI in the   browser's address bar).  As such, there is a considerable risk that   the access URI instead of the reference URI is used for referencing   [PIDs-must-be-used].   The link relation type defined in this document makes it possible for   user agents to differentiate the reference URI from the access URI.Van de Sompel, et al.         Informational                     [Page 4]

RFC 8574            The "cite-as" Link Relation Type          April 20193.2.  Version Identifiers   Resource versioning systems often use a naming approach whereby:   o  The most recent version of a resource is always available at the      same, generic URI.   o  Each version of the resource -- including the most recent one --      has a distinct version URI.   For example, Wikipedia uses generic URIs of the form   <https://en.wikipedia.org/wiki/John_Doe> and version URIs of the form   <https://en.wikipedia.org/w/index.php?title=John_Doe&oldid=   776253882>.   While the current version of a resource is accessed at the generic   URI, some versioning systems adhere to a policy that favors linking   and referencing a specific version URI.  To express this using the   terminology ofSection 2, these policies intend that the generic URI   is the access URI and that the version URI is the reference URI.   These policies are informed by the understanding that the content at   the generic URI is likely to evolve over time and that accurate links   or references should lead to the content as it was at the time of   referencing.  To that end, Wikipedia's "Permanent link" and "Cite   this page" functionalities promote the version URI, not the generic   URI.   The link relation type defined in this document makes it possible for   user agents to differentiate the version URI from the generic URI.3.3.  Preferred Social Identifier   A web user commonly has multiple profiles on the Web, for example,   one per social network, a personal homepage, a professional homepage,   a FOAF (Friend Of A Friend) profile [FOAF], etc.  Each of these   profiles is accessible at a distinct URI.  But the user may have a   preference for one of those profiles, for example, because it is most   complete, kept up to date, or expected to be long lived.  As an   example, the first author of this document has, among others, the   following profile URIs:   o  <https://hvdsomp.info>   o  <https://twitter.com/hvdsomp>   o  <https://www.linkedin.com/in/herbertvandesompel/>   o  <https://orcid.org/0000-0002-0715-6126>Van de Sompel, et al.         Informational                     [Page 5]

RFC 8574            The "cite-as" Link Relation Type          April 2019   Of these, from the perspective of the person described by these   profiles, the first URI may be the preferred profile URI for the   purpose of referencing because the domain is not under the   custodianship of a third party.  When an agent accesses another   profile URI, such as <https://orcid.org/0000-0002-0715-6126>, this   preference for referencing by means of the first URI could be   expressed.   The link relation type defined in this specification makes it   possible for user agents to differentiate the preferred profile URI   from the accessed profile URI.3.4.  Multi-resource Publications   When publishing on the Web, it is not uncommon to make distinct   components of a publication available as different web resources,   each with their own URI.  For example:   o  Contemporary scholarly publications routinely consists of a      traditional article as well as additional materials that are      considered an integral part of the publication such as      supplementary information, high-resolution images, or a video      recording of an experiment.   o  Scientific or governmental open data sets frequently consist of      multiple files.   o  Online books typically consist of multiple chapters.   While each of these components is accessible at its distinct URI --   the access URI -- they often also share a URI assigned to the   intellectual publication of which they are components -- the   reference URI.   The link relation type defined in this document makes it possible for   user agents to differentiate the URI of the intellectual publication   from the access URI of a component of the publication.4.  The "cite-as" Link Relation Type for Expressing a Preferred URI for    the Purpose of Referencing   A link with the "cite-as" relation type indicates that, for   referencing the link context, use of the URI of the link target is   preferred over use of the URI of the link context.  It allows the   resource identified by the access URI (link context) to unambiguously   link to its corresponding reference URI (link target), thereby   expressing that the link target is preferred over the link context   for the purpose of permanent citation.Van de Sompel, et al.         Informational                     [Page 6]

RFC 8574            The "cite-as" Link Relation Type          April 2019   The link target of a "cite-as" link SHOULD support protocol-based   access as a means to ensure that applications that store them can   effectively reuse them for access.   The link target of a "cite-as" link SHOULD provide the ability for a   user agent to follow its nose back to the context of the link, e.g.,   by following redirects and/or links.  This helps a user agent to   establish trust in the target URI.   Because a link with the "cite-as" relation type expresses a preferred   URI for the purpose of referencing, the access URI SHOULD only   provide one link with that relation type.  If more than one "cite-as"   link is provided, the user agent may decide to select one (e.g., an   HTTP URI over a mailto URI) based on the purpose that the reference   URI will serve.   Providing a link with the "cite-as" relation type does not prevent   using the access URI for the purpose of referencing if such   specificity is needed for the application at hand.  For example, in   the case of the scenario inSection 3.4, the access URI is likely   required for the purpose of annotating a specific component of an   intellectual publication.  Yet, the annotation application may also   want to appropriately include the reference URI in the annotation.   Applications can leverage the information provided by a "cite-as"   link in a variety of ways, for example:   o  Bookmarking tools and citation managers can take this preference      into account when recording a URI.   o  Webometrics applications that trace URIs can trace both the access      URI and the reference URI.   o  Discovery tools can support lookup by means of both the access and      the reference URI.  This includes web archives that typically make      archived versions of web resources discoverable by means of the      original access URI of the archived resource; they can      additionally make these archived resources discoverable by means      of the associated reference URI.Van de Sompel, et al.         Informational                     [Page 7]

RFC 8574            The "cite-as" Link Relation Type          April 20195.  Distinction with Other Link Relation Types   Some existing IANA-registered relationships intuitively resemble the   relationship that "cite-as" is intended to convey.  But a closer   inspection of these candidates provided in the blog posts   [identifier-blog], [canonical-blog], and [bookmark-blog] shows that   they are not appropriate for various reasons and that a new link   relation type is required.  The remainder of this section provides a   summary of the detailed explanations provided in the referenced blog   posts.   It can readily be seen that the following link relation types do not   address the requirements described inSection 3:   o  "alternate" [RFC4287]: The link target provides an alternate      version of the content at the link context.  These are typically      variants according to dimensions that are subject to content      negotiation, for example, the same content with varying Content-      Type (e.g., application/pdf vs. text/html) and/or Content-Language      (e.g., en vs. fr).  The representations provided by the context      URIs and target URIs in the scenarios in Sections3.1 through3.4      are not variants in the sense intended by [RFC4287], and, as such,      the use of "alternate" is not appropriate.   o  "duplicate" [RFC6249]: The link target is a resource whose      available representations are byte-for-byte identical with the      corresponding representations of the link context, for example, an      identical file on a mirror site.  In none of the scenarios      described in Sections3.1 through3.4 do the link context and the      link target provide identical content.  As such, the use of      "duplicate" is not appropriate.   o  "related" [RFC4287]: The link target is a resource that is related      to the link context.  While "related" could be used in all of the      scenarios described in Sections3.1 through3.4, its semantics are      too vague to convey the specific semantics intended by "cite-as".   Two existing IANA-registered relationships deserve closer attention   and are discussed in the remainder of this section.Van de Sompel, et al.         Informational                     [Page 8]

RFC 8574            The "cite-as" Link Relation Type          April 20195.1.  The "bookmark" Link Relation Type   "bookmark" [W3C.REC-html52-20171214]: The link target provides a URI   for the purpose of bookmarking the link context.   The intent of "bookmark" is closest to that of "cite-as" in that the   link target is intended to be a permalink for the link context, for   bookmarking purposes.  The link relation type dates back to the   earliest days of news syndication, before blogs and news feeds had   permalinks to identify individual resources that were aggregated into   a single page.  As such, its intent is to provide permalinks for   different sections of an HTML document.  It was originally used with   HTML elements such as <div>, <h1>, <h2>, etc.; more recently, HTML5   revised it to be exclusively used with the <article> element.   Moreover, it is explicitly excluded from use in the <link> element in   HTML <head> and, as a consequence, in the HTTP Link header that is   semantically equivalent.  For these technical and semantic reasons,   the use of "bookmark" to convey the relationship intended by "cite-   as" is not appropriate.   A more detailed justification regarding the inappropriateness of   "bookmark", including a thorough overview of its turbulent history,   is provided in [bookmark-blog].5.2.  The "canonical" Link Relation Type   "canonical" [RFC6596]: The meaning of "canonical" is commonly   misunderstood on the basis of its brief definition as being "the   preferred version of a resource."  The description in the abstract of   [RFC6596] is more helpful and states that "canonical" is intended to   link to a resource that is preferred over resources with duplicative   content.  A more detailed reading of [RFC6596] clarifies that the   intended meaning is that "canonical" is preferred for the purpose of   content indexing.  A typical use case is linking from each page in a   multi-page magazine article to a single page version of the article   provided for indexing by search engines: the former pages provide   content that is duplicative to the superset content that is available   at the latter page.   The semantics intended by "canonical" as preferred for the purpose of   content indexing differ from the semantics intended by "cite-as" as   preferred for the purpose of referencing.  A further exploration of   the various scenarios shows that the use of "canonical" is not   appropriate to convey the semantics intended by "cite-as":Van de Sompel, et al.         Informational                     [Page 9]

RFC 8574            The "cite-as" Link Relation Type          April 2019   o  Scenario ofSection 3.1: The reference URI that is intended to be      persistent over time does not serve content that needs to be      indexed; it merely redirects to the access URI.  Since the meaning      intended by "canonical" is that it is preferred for the purpose of      content indexing, it is not appropriate to point at the reference      URI (persistent identifier) using the "canonical" link relation      type.  Moreover,Section 6.1 shows that scholarly publishers that      assign persistent identifiers already use the "canonical" link      relation type for search engine optimization; it also shows how      that use contrasts with the intended use of "cite-as".   o  Scenario ofSection 3.2: In most common cases, custodians of      resource versioning systems want search engines to index the most      recent version of a page and hence would use a "canonical" link to      point from version URIs of a resource to the associated generic      URI.  Wikipedia effectively does this.  However, for some resource      versioning systems, including Wikipedia, version URIs are      preferred for the purpose of referencing.  As such, a "cite-as"      link would point from the generic URI to the most recent version      URI (that is, in the opposite direction of the "canonical" link).   o  Scenario ofSection 3.3: The content at the link target and the      link context are different profiles for a same person.  Each      profile, not just a preferred one, should be indexed.  But a      single one could be preferred for referencing.   o  Scenario ofSection 3.4: The content at the link target, if any,      would typically be a landing page that includes descriptive      metadata pertaining to the multi-resource publication and links to      its component resources.  Each component resource provides content      that is different, not duplicative, to the landing page.   A more detailed justification regarding how the use of "canonical" is   inappropriate to address the requirements described in this document,   including examples, is provided in [canonical-blog].6.  Examples   Sections6.1 through6.4 show examples of the use of links with the   "cite-as" relation type.  They illustrate how the typed links can be   used in a response header and/or response body.Van de Sompel, et al.         Informational                    [Page 10]

RFC 8574            The "cite-as" Link Relation Type          April 20196.1.  Persistent HTTP URI   PLOS ONE is one of many scholarly publishers that assigns DOIs to the   articles it publishes.  For example, <https://doi.org/10.1371/journal.pone.0171057> is the persistent identifier for such an   article.  Via the DOI resolver, this persistent identifier redirects   to <https://journals.plos.org/plosone/doi?id=10.1371/journal.pone.0171057> in the plos.org domain.  This URI itself   redirects to <https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0171057>, which delivers the actual article in HTML.   The HTML article contains a <link> element with the "canonical" link   relation type pointing at itself, <https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0167475>.  As perSection 5.2, this   indicates that the article content at that URI should be indexed by   search engines.   PLOS ONE can additionally provide a link with the "cite-as" relation   type pointing at the persistent identifier to indicate it is the   preferred URI for permanent citation of the article.  Figure 1 shows   the addition of the "cite-as" link in both the HTTP header and the   HTML that results from an HTTP GET on the article URI   <https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0167475>.   HTTP/1.1 200 OK   Link: <https://doi.org/10.1371/journal.pone.0171057> ; rel="cite-as"   Content-Type: text/html;charset=utf-8   <html>    <head>    ...     <link rel="cite-as"           href="https://doi.org/10.1371/journal.pone.0171057" />     <link rel="canonical"           href="https://journals.plos.org/plosone/article?                              id=10.1371/journal.pone.0167475" />    ...    </head>    <body>     ...    </body>   </html>     Figure 1: Response to HTTP GET on the URI of a Scholarly ArticleVan de Sompel, et al.         Informational                    [Page 11]

RFC 8574            The "cite-as" Link Relation Type          April 20196.2.  Version URIs   The preprint server arXiv.org has a versioning approach like the one   described inSection 3.2:   o  The most recent version of a preprint is always available at the      same, generic URI.  Consider the preprint with generic URI      <https://arxiv.org/abs/1711.03787>.   o  Each version of the preprint -- including the most recent one --      has a distinct version URI.  The considered preprint has two      versions with respective version URIs: <https://arxiv.org/abs/1711.03787v1> (published 10 November 2017) and      <https://arxiv.org/abs/1711.03787v2> (published 24 January 2018).   A reader who accessed <https://arxiv.org/abs/1711.03787> between 10   November 2017 and 23 January 2018, obtained the first version of the   preprint.  Starting 24 January 2018, the second version was served at   that URI.  In order to support accurate referencing, arXiv.org could   implement the "cite-as" link to point from the generic URI to the   most recent version URI.  In doing so, assuming the existence of   reference manager tools that consume "cite-as" links:   o  The reader who accesses <https://arxiv.org/abs/1711.03787> between      10 November 2017 and 23 January 2018 would reference      <https://arxiv.org/abs/1711.03787v1>.   o  The reader who accesses <https://arxiv.org/abs/1711.03787>      starting 24 January 2018 would reference <https://arxiv.org/abs/1711.03787v2>.   Figure 2 shows the header that arXiv.org would have returned in the   first case, in response to a HTTP HEAD on the generic URI   <https://arxiv.org/abs/1711.03787>.   HTTP/1.1 200 OK   Date: Sun, 24 Dec 2017 16:12:43 GMT   Content-Type: text/html; charset=utf-8   Link: <https://arxiv.org/abs/1711.03787v1> ; rel="cite-as"   Vary: Accept-Encoding,User-Agent     Figure 2: Response to HTTP HEAD on the Generic URI of the Landing                       Page of an arXiv.org PreprintVan de Sompel, et al.         Informational                    [Page 12]

RFC 8574            The "cite-as" Link Relation Type          April 20196.3.  Preferred Profile URI   If the access URI is the home page of John Doe, John can add a link   with the "cite-as" relation type to it, in order to convey that he   would prefer to be referenced by means of the URI of his FOAF   profile.  Figure 3 shows the response to an HTTP GET on the URI of   John's home page.   HTTP/1.1 200 OK   Content-Type: text/html;charset=utf-8   <html>    <head>    ...     <link rel="cite-as" href="http://johndoe.example.com/foaf"           type="text/ttl"/>    ...    </head>    <body>     ...    </body>   </html>     Figure 3: Response to HTTP GET on the URI of John Doe's Home Page6.4.  Multi-resource Publication   The Dryad Digital Repository at datadryad.org specializes in hosting   and preserving scientific datasets.  Each dataset typically consists   of multiple resources.  For example, the dataset "Data from: Climate,   demography, and lek stability in an Amazonian bird" consists of an   Excel spreadsheet, a csv file, and a zip file.  Each of these   resources have different content and are accessible at their   respective URIs.  In addition, the dataset has a landing page at   <https://datadryad.org/resource/doi:10.5061/dryad.5d23f>.   Each of these resources should be permanently cited by means of the   persistent identifier that was assigned to the entire dataset as an   intellectual publication, i.e., <https://doi.org/10.5061/dryad.5d23f>.  To that end, the Dryad Digital Repository can add   "cite-as" links pointing from the URIs of each of these resources to   <https://doi.org/10.5061/dryad.5d23f>.  This is shown in Figure 4 for   the csv file that is a component resource of the dataset, through use   of the HTTP Link header.Van de Sompel, et al.         Informational                    [Page 13]

RFC 8574            The "cite-as" Link Relation Type          April 2019   HTTP/1.1 200 OK   Date: Tue, 12 Jun 2018 19:19:22 GMT   Last-Modified: Wed, 17 Feb 2016 18:37:02 GMT   Content-Type: text/csv;charset=ISO-8859-1   Content-Length: 25414   Link: <https://doi.org/10.5061/dryad.5d23f> ; rel="cite-as"   DATE,Year,PLOT/TRAIL,LOCATION,SPECIES CODE,BAND NUM,COLOR,SEX,AGE,    TAIL,WING,TARSUS,NARES,DEPTH,WIDTH,WEIGHT   6/26/02,2002,DANTA,325,PIPFIL,969,B/O,M,AHY,80,63,16,7.3,3.9,4.1,    14.4   ...   2/3/13,2013,LAGO,,PIPFIL,BR-5095,O/YPI,M,SCB,78,65.5,14.2,7.5,3.8,    3.7,14.3     Figure 4: Response to HTTP GET on the URI of a csv File That Is a                     Component of a Scientific Dataset7.  IANA Considerations   The link relation type has been registered by IANA perSection 2.1.1   of [RFC8288] as follows:      Relation Name: cite-as      Description: Indicates that the link target is preferred over the      link context for the purpose of permanent citation.      Reference:RFC 85748.  Security Considerations   In cases where there is no way for the agent to automatically verify   the correctness of the reference URI (cf.Section 4), out-of-band   mechanisms might be required to establish trust.   If a trusted site is compromised, the "cite-as" link relation could   be used with malicious intent to supply misleading URIs for   referencing.  Use of these links might direct user agents to an   attacker's site, break the referencing record they are intended to   support, or corrupt algorithmic interpretation of referencing data.Van de Sompel, et al.         Informational                    [Page 14]

RFC 8574            The "cite-as" Link Relation Type          April 20199.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC4287]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom              Syndication Format",RFC 4287, DOI 10.17487/RFC4287,              December 2005, <https://www.rfc-editor.org/info/rfc4287>.   [RFC5988]  Nottingham, M., "Web Linking",RFC 5988,              DOI 10.17487/RFC5988, October 2010,              <https://www.rfc-editor.org/info/rfc5988>.   [RFC6249]  Bryan, A., McNab, N., Tsujikawa, T., Poeml, P., and H.              Nordstrom, "Metalink/HTTP: Mirrors and Hashes",RFC 6249,              DOI 10.17487/RFC6249, June 2011,              <https://www.rfc-editor.org/info/rfc6249>.   [RFC6596]  Ohye, M. and J. Kupke, "The Canonical Link Relation",RFC 6596, DOI 10.17487/RFC6596, April 2012,              <https://www.rfc-editor.org/info/rfc6596>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174,              May 2017, <https://www.rfc-editor.org/info/rfc8174>.   [RFC8288]  Nottingham, M., "Web Linking",RFC 8288,              DOI 10.17487/RFC8288, October 2017,              <https://www.rfc-editor.org/info/rfc8288>.   [W3C.REC-html52-20171214]              Faulkner, S., Eicholz, A., Leithead, T., Danilo, A., and              S. Moon, "HTML 5.2", World Wide Web              Consortium Recommendation REC-html52-20171214, December              2017, <https://www.w3.org/TR/2017/REC-html52-20171214/>.9.2.  Informative References   [ARK]      Kunze, J. and R. Rodgers,"The ARK Identifier Scheme",              Work in Progress,draft-kunze-ark-18, April 2013.Van de Sompel, et al.         Informational                    [Page 15]

RFC 8574            The "cite-as" Link Relation Type          April 2019   [bookmark-blog]              Nelson, M. and H. Van de Sompel, "rel=bookmark also does              not mean what you think it means", August 2017,              <http://ws-dl.blogspot.com/2017/08/2017-08-26-relbookmark-also-does-not.html>.   [canonical-blog]              Nelson, M. and H. Van de Sompel, "rel=canonical does not              mean what you think it means", August 2017,              <http://ws-dl.blogspot.nl/2017/08/2017-08-07-relcanonical-does-not-mean.html>.   [CoolURIs]              Berners-Lee, T., "Cool URIs don't change", World Wide Web              Consortium Style, 1998,              <https://www.w3.org/Provider/Style/URI.html>.   [DOI-URLs]              Hendricks, G., "Display guidelines for Crossref DOIs",              March 2017,              <https://blog.crossref.org/display-guidelines/>.   [DOIs]     ISO, "Information and documentation - Digital object              identifier system", ISO 26324:2012(en), 2012,              <https://www.iso.org/obp/ui/              #iso:std:iso:26324:ed-1:v1:en>.   [FOAF]     Brickley, D. and L. Miller, "FOAF Vocabulary Specification              0.99", January 2014, <http://xmlns.com/foaf/spec/>.   [identifier-blog]              Nelson, M. and H. Van de Sompel, "Linking to Persistent              Identifiers with rel=identifier", November 2016,              <http://ws-dl.blogspot.com/2016/11/2016-11-07-linking-to-persistent.html>.   [PIDs-must-be-used]              Van de Sompel, H., Klein, M., and S. Jones, "Persistent              URIs Must Be Used To Be Persistent", February 2016,              <https://arxiv.org/abs/1602.09102>.   [PURLs]    Wikipedia, "Persistent uniform resource locator",              September 2018, <https://en.wikipedia.org/w/index.php?title=Persistent_uniform_resource_locator&oldid=858558072>.Van de Sompel, et al.         Informational                    [Page 16]

RFC 8574            The "cite-as" Link Relation Type          April 2019Acknowledgements   The authors would like to thank the following individuals for their   comments and suggestions: Martin Klein, Harihar Shankar, Peter   Williams, John Howard, Mark Nottingham, and Graham Klyne.Authors' Addresses   Herbert Van de Sompel   Data Archiving and Networked Services   Email: herbert.van.de.sompel@dans.knaw.nl   URI:https://orcid.org/0000-0002-0715-6126   Michael Nelson   Old Dominion University   Email: mln@cs.odu.edu   URI:http://www.cs.odu.edu/~mln/   Geoffrey Bilder   Crossref   Email: gbilder@crossref.org   URI:https://www.crossref.org/authors/geoffrey-bilder/   John Kunze   California Digital Library   Email: jak@ucop.edu   URI:https://orcid.org/0000-0001-7604-8041   Simeon Warner   Cornell University   Email: simeon.warner@cornell.edu   URI:https://orcid.org/0000-0002-7970-7855Van de Sompel, et al.         Informational                    [Page 17]