Network Working Group E. Wilde Internet-Draft CA Technologies Intended status: Informational H. Van de Sompel Expires: March 21, 2019 Los Alamos National Laboratory September 17, 2018 Linkset: Media Types and a Link Relation Type for Link Sets draft-wilde-linkset-03 Abstract This specification defines two media types and a link relation type for sets of links. The media types can be used to represents links in a standalone fashion, in one case in the native format used in the HTTP Link header, and in the other case in a JSON-based format. The link relation can be used to reference these kind of standalone link sets, so that a resource can indicate that additional links putting it into context are available someplace else. One typical scenario is when the number of links to put in an HTTP Link header field becomes too big, and thus these links should be provided by a distinct resource. Note to Readers Please discuss this draft on the ART mailing list (). Online access to all versions and files is available on GitHub (). Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on March 21, 2019. Wilde & Van de Sompel Expires March 21, 2019 [Page 1] Internet-Draft Linkset September 2018 Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Third-Party Links . . . . . . . . . . . . . . . . . . . . 4 3.2. Challenges Writing to HTTP Link Header Field . . . . . . 4 3.3. Large Number of Links . . . . . . . . . . . . . . . . . . 5 4. Document Formats for Link Sets . . . . . . . . . . . . . . . 5 4.1. HTTP Link Document Format: application/linkset . . . . . 6 4.2. JSON Document Format: application/linkset+json . . . . . 6 4.2.1. Link Sets . . . . . . . . . . . . . . . . . . . . . . 6 4.2.2. Links . . . . . . . . . . . . . . . . . . . . . . . . 6 4.2.3. Link Target Attributes . . . . . . . . . . . . . . . 7 4.2.4. Extension Target Attributes . . . . . . . . . . . . . 9 5. The "linkset" Relation Type for Linking to Link Sets . . . . 10 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. Links Provided in the Header of the Link Set Resource . . 12 6.2. Links Provided in the Body of the Link Set Resource, Link Set Serialized as application/linkset+json . . . . . 13 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 15 7.1. Open Journal Systems (OJS) . . . . . . . . . . . . . . . 16 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 8.1. Link Relation Type: linkset . . . . . . . . . . . . . . . 16 8.2. Media Type: application/linkset . . . . . . . . . . . . . 16 8.2.1. IANA Considerations . . . . . . . . . . . . . . . . . 16 8.3. Media Type: application/linkset+json . . . . . . . . . . 17 9. Security Considerations . . . . . . . . . . . . . . . . . . . 18 10. Normative References . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Wilde & Van de Sompel Expires March 21, 2019 [Page 2] Internet-Draft Linkset September 2018 1. Introduction Resources on the Web often convey typed Web Links [RFC8288] as a part of resource representations, for example, using the element for HTML representations, or the "Link" header field in HTTP response headers for representations of any media type. In some cases, however, providing links by value is impractical or impossible. In these cases, an approach to provide links by reference (instead of by value) can solve the problem. To that end, this specification defines two document formats and associated media types to represent a set of links. It also defines the "linkset" relation type that a resource can use to support discovery of another resource that conveys links in which the former resource participates. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. This specification uses the terms "link context" and "link target" as defined in [RFC8288]. (These terms respectively correspond with "Context IRI" and "Target IRI" as used in RFC 8288 [RFC8288]). Although defined as IRIs, in common scenarios they are also URIs. Additionally, this specification uses the following terms for types of resources involved in providing links by reference: o A "link set resource" is a resource that conveys a set of links. Section 4 defines two representations for a set of links, based on the abstract link model defined in [RFC8288]. o An "origin resource" is a resource that participates in one or more links provided by a link set resource. An origin resource can support discovery of an associated link set resource by using the relation type defined in Section 5. As such, from the perspective of the origin resource, the links conveyed by the link set resource are provided by reference. 3. Scenarios The following sections outline some scenarios in which it is useful to have the ability to separate resources from the links that pertain to them. Wilde & Van de Sompel Expires March 21, 2019 [Page 3] Internet-Draft Linkset September 2018 These are all scenarios in which providing links by reference is advantageous or necessary. It is important to keep in mind that, when providing some links by reference, some/other links can still be provided by value. 3.1. Third-Party Links In some cases, it is useful that links pertaining to an origin resource are provided by a server other than the one that hosts the origin resource. For example, this allows: o Providing links in which the origin resource is involved not just as link context but also as link target. o Providing links pertaining to the origin resource that the server hosting that resource is not aware of. o External management of links pertaining to the origin resource in a special-purpose link management service. In such cases, a third-party link set resource provides links pertaining to the origin resource. This link set resource may be managed by the same custodian as the origin resource, or by a third party. In order for the server hosting the origin resource to provide an up- to-date and complete set of links in which the origin resource participates, the server would need to obtain the links from the link set resource, and embed them in the origin resource's representations prior to responding to a client. Doing so would increase latency and load, which may be unnecessary if a client is not intent on consuming these links. Providing links by reference, instead of by value, removes the server-to-server communication and resulting overhead required to obtain links. Instead, the consumer of the origin resource can decide if they need the additional links as context for the resource. 3.2. Challenges Writing to HTTP Link Header Field In some cases, it is not straightforward to write links to the HTTP Link header field from an application. This can, for example, be the case because not all required link information is available to the application or because the application does not have the capability to directly write HTTP headers. In such cases, providing links by reference can be a solution because a link to a link set resource associated with an origin resource can typically be added by means of a web server rewrite rule that leverages the resource's URI. Wilde & Van de Sompel Expires March 21, 2019 [Page 4] Internet-Draft Linkset September 2018 3.3. Large Number of Links When conveying links in the HTTP "Link" header, it is possible for the size of the HTTP response header to become unpredictable. This can be the case when links are determined dynamically dependent on a range of contextual factors. It is possible to statically configure a web server to correctly handle large HTTP response headers by specifying an upper boundary for their size. But when the number of links is unpredictable, estimating a reliable upper boundary is challenging. HTTP [RFC7231] defines error codes related to excess communication by the user agent ("413 Request Entity Too Large" and "414 Request-URI Too Long"), but no specific error codes are defined to indicate that response header content exceeds the upper boundary that can be handled by the server, and thus it has been truncated. As a result, applications take counter measures aimed at controlling the size of the HTTP "Link" header, for example by limiting the links they provide to those with select relation types, thereby limiting the value of the HTTP "Link" header to clients. Providing links by reference, instead of by value, overcomes challenges related to the unpredictable nature of the extent of HTTP "Link" headers. In more extreme scenarios it is conceivable that the number of links pertaining to the origin resource becomes so large that the response from the associated link set resource becomes too large. This could be the case for highly popular origin resources, when the link set includes links in which the origin resource participates as both link context and link target. In such cases, the link set resource could deliver responses incrementally, for example, using a paged resource model that clients can consume as required. 4. Document Formats for Link Sets Link set resources can be represented by serializations that support conveying both link contexts and link targets. This section specifies two document formats based on the abstract model specified in Section 2 of [RFC8288] that defines a link as consisting of a "link context", a "link relation type", a "link target", and optional "target attributes". In those terms, a link set resource is a resource that conveys a collection of one or more such links. The format defined in Section 4.1 is identical to the payload of the HTTP Link header as specified in [RFC8288]. The format defined in Section 4.2 is based on JSON and thus does not have the character encoding limitations of HTTP header fields. Wilde & Van de Sompel Expires March 21, 2019 [Page 5] Internet-Draft Linkset September 2018 4.1. HTTP Link Document Format: application/linkset This document format is identical to the payload of the HTTP Link header. It is defined in Section 3 of [RFC8288], more specifically by its ABNF production rule for "Link" and subsequent ones. The assigned media type for this format is "application/linkset". 4.2. JSON Document Format: application/linkset+json This document format is based on the native Link header field representation defined by [RFC8288], but uses JSON [RFC8259] as the syntax to represent the information contained in the native format. It is described in this section. The assigned media type for this format is "application/linkset+json". 4.2.1. Link Sets In the JSON representation of a link set: o A link set MUST be represented as a JSON array. o A distinct JSON object - the "link object" - in this array MUST be used to represent an individual link or multiple links that have the same link context and link target. (see Section 4.2.2). o Implementations MUST wrap link objects in an array, even if the link set contains only one link. o Implementations MUST NOT include any members other than link objects in the array that represents a link set. 4.2.2. Links In the JSON representation, individual links (as well as multiple links that have the same link context and link target) are represented by a JSON object, the link object. A link object adheres to the following rules: o Each link object MUST have an "href" member with a value that represents the link target. o Each link object MAY have an "anchor" member with a value that represents the link context. If this member is not provided, the link context is the link set resource. o The value of both the "href" and "anchor" members MUST be a URI- reference as defined in Section 4.1 of [RFC3986]. Note that for Wilde & Van de Sompel Expires March 21, 2019 [Page 6] Internet-Draft Linkset September 2018 relative references, the baseURI is the URI of the link set resource. o Each link object MUST have a "rel" or "rev" member (with the latter one deprecated) with a value that represents one or more link relation types, represented as an array of strings. The value of each "rel"/"rev" link relation type MUST either be a registered relation type or an extension relation type (URI), as described in Sections 2.1.1 and 2.1.2 of [RFC8288], respectively. o Each link object MAY have additional members representing target attributes (see Section 4.2.3). The following example of a JSON-serialized link set represents one link with the core components of a link: link context, link relation type, and link target. [ { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "next" ] } ] The following example of a JSON-serialized link set represents two links with the core components of a link: link context, link relation type, and link target. The syntax of this example takes advantage of the fact that multiple relation types can be used in one link object to represent multiple links that have the same link context and link target. [ { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "next" , "http://example.net/linkrel" ] } ] The previous example is equivalent to the following one, which does not use the syntax shortcut and therefore represents the two links individually. [ { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "next" ] }, { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "http://example.net/linkrel" ] } ] 4.2.3. Link Target Attributes In many cases, a link is further qualified by target attributes, either defined by the serialization of [RFC8288] or extension attributes defined and used by communities. Wilde & Van de Sompel Expires March 21, 2019 [Page 7] Internet-Draft Linkset September 2018 4.2.3.1. JSON Representation of RFC 8288 Target Attributes RFC 8288 defines the following target attributes that may be used to annotate links: "hreflang", "media", "title", "title*", and "type". These target attributes follow different occurrence and value patterns and MUST be handled in the JSON representation as follows: o "hreflang": The optional and repeatable "hreflang" target attribute MUST be represented by an array (even if there only is one value to be represented), and each value in that array MUST be a string - representing one value of the "hreflang" target attributes for a link - which follows the same model as in the [RFC8288] syntax. o "media": The optional and not repeatable "media" target attribute MUST be represented by a "media" member in the link object, and its value MUST be a string that follows the same model as in the [RFC8288] syntax. o "type": The optional and not repeatable "type" target attribute MUST be represented by a "type" member in the link object, and its value MUST be a string that follows the same model as in the [RFC8288] syntax. o "title": The optional and not repeatable "title" target attribute MUST be represented by a "title" member in the link object, and its value MUST be a string that follows the same model as in the [RFC8288] syntax. o "title*": The optional and not repeatable "title*" target attribute is motivated by character encoding and language issues and follows the model defined in [RFC8187]. The details of the JSON representation that applies to title* are described in Section 4.2.3.2. The following example illustrates how the repeatable "hreflang" and the not repeatable "type" target attributes are represented in a link object. [ { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "next" ], "hreflang" : [ "en" , "de" ], "type" : "text/html" } ] Wilde & Van de Sompel Expires March 21, 2019 [Page 8] Internet-Draft Linkset September 2018 4.2.3.2. Internationalized Target Attributes for a Link In addition to the target attributes described in Section 4.2.3, [RFC8288] also supports attributes that follow the content model of [RFC8187]. In [RFC8288], these target attributes are recognizable by the use of a trailing asterisk in the attribute name, such as "title*". The content model of [RFC8187] uses a string-based microsyntax that represents the character encoding, an optional language tag, and the escaped attribute value encoded according to the specified character encoding. The JSON serialization for these attributes is as follows: o Internationalized target attributes use the attribute name (including the *) as their name. o The character encoding information as prescribed by [RFC8187] is not preserved; instead, the attribute value is represented in the character encoding used for the JSON link set. o The attribute value is an array that contains one or more arrays. In each of these arrays, the first value is a string representing the attribute value (in its unescaped version), and the optional second array value is a language tag [RFC5646] associated with that attribute value. The following example illustrates how the "title*" target attribute defined by [RFC8288] is represented in a link object. [ { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "next" ], "title*" : [ [ "nachstes Kapitel", "de" ] ] } ] The above example assumes that the german title contains an umlaut character (which in the native syntax would be encoded as title*=UTF- 8'de'n%c3%a4chstes%20Kapitel), which gets encoded in its unescaped form (but not shown here due to the limitations of RFC publication) in the JSON representation. Implementations MUST properly decode/ encode RFC 8187 style target attributes when transcoding between the native and the JSON syntax. 4.2.4. Extension Target Attributes Extension target attributes are attributes that are not defined by RFC 8288 (as listed in Section 4.2.3.1), but are nevertheless used to qualify links. They can be defined by communities in any way deemed necessary, and it is up to them to make sure their usage is Wilde & Van de Sompel Expires March 21, 2019 [Page 9] Internet-Draft Linkset September 2018 understood by target applications. However, lacking standardization, there is no interoperable understanding of these extension attributes. One important consequence is that their cardinality is unknown to generic applications. Therefore, in the JSON serialization, all extension target attributes are treated as repeatable: o Extension target attributes use the attribute name (including the *, if applicable) as their name. o The value of an extension attribute MUST be represented by an array (even if there only is one value to be represented). o If the extension attribute does not have a name with a trailing asterisk, then each value in that array MUST be a string that represents one value of the extension target attribute. o If the extension attribute has a name with a trailing asterisk (it follows the content model of [RFC8187]), then each value in that array MUST be an array. The value of each array MUST be structured as described in Section 4.2.3.2. [ { "href" : "http://example.com/foo", "anchor" : "http://example.net/bar", "rel" : [ "next" ], "foo" : [ "foovalue" ], "bar" : [ "barone", "bartwo" ], "baz*" : [ [ "bazvalue", "en" ] ] } ] The example shows a link object with three extension target attributes. Every extension target attribute is represented by an array. The two first ones are regular extension target attributes, with the first one ("foo") having only one value, while the second one ("bar") appeared twice and thus there are two values to represent. The last extension target attribute ("baz" follows the naming rule of RFC 8187 and therefore is encoded according to the rules described in Section Section 4.2.3.2. Specifically, the array representing the extension target attribute contains arrays, each of which represents the value itself, and the language tag (if one is specified). 5. The "linkset" Relation Type for Linking to Link Sets The target of a link with the "linkset" relation type - the link set resource - provides a set of links, including links in which the link context - the origin resource - participates. Wilde & Van de Sompel Expires March 21, 2019 [Page 10] Internet-Draft Linkset September 2018 A link with the "linkset" relation type MAY be provided in the header and/or the body of the origin resource's representation. It may also be discovered by other means, such as through client-side information. More than one link with a "linkset" relation type MAY be provided. Multiple such links can refer to the same set of links expressed using different representations, or to different sets of links (potentially provided by different services). The use of a link with the "linkset" relation type does not preclude the provision of links with other relation types, i.e. the origin resource can provide typed links other than a "linkset" link. Therefore, the effective set of links pertaining to the origin resource is the union of the links that the resource itself provides, and of all links - provided by the link set resource - in which it participates. The link set resource MAY provide the links that pertain to the origin resource in its HTTP response header and/or body. In common scenarios (the origin resource is distinct from the link set resource), it is essential for link set representations to make the URI of the origin resource explicit for those links in which the origin resource acts as link context. A user agent that follows a "linkset" link from an origin resource MUST be aware that the link set resource can provide links in which the origin resource does not participate and MAY decide to ignore those links. There is no constraint on the target URI of a link with the "linkset" relation type; designing and using these URIs is left to the discretion of implementers. If an origin resource provides a "linkset" link pointing at a link set resource, and that link set resource provides a "linkset" link in turn, then this latter link points at links pertaining to the link set resource. This means that in the context of the latter link, the link set resource is an origin resource. This means that linkset relations are not transitive, and it is up to a client to decide whether they follow "nested chains" of "linkset" links or not. 6. Examples Sections Section 6.1 and Section 6.2 show examples whereby the link set resource provides links pertaining to the origin resource, in its response header and body, respectively. Wilde & Van de Sompel Expires March 21, 2019 [Page 11] Internet-Draft Linkset September 2018 6.1. Links Provided in the Header of the Link Set Resource Figure 1 shows a client issuing an HTTP head request against origin resource http://example.org/resource1. HEAD /resource1 HTTP/1.1 Host: example.org Connection: close Figure 1: Client HTTP HEAD Request Figure 2 shows the response to the HEAD request of Figure 1. The response contains a Link header with a link that uses the "linkset" relation type. It indicates that links pertaining to the origin resource are provided by link set resource http://example.com/ links?uri=http%3A%2F%2Fexample.org%2Fresource. HTTP/1.1 200 OK Date: Mon, 28 Nov 2016 14:37:51 GMT Server: Apache-Coyote/1.1 Link: ; rel="linkset" ; type="text/html" Content-Length: 5214 Content-Type: text/html;charset=utf-8 Connection: close Figure 2: Response to HTTP HEAD on Origin Resource While in this example the URI of the link set resource uses a pattern that represents the URI of the origin resource, this is opaque to the client, which simply follows target URI to retrieving the link set resource. Figure 3 shows the client issuing an HTTP GET request against the link set resource provided in Figure 2. GET /links?uri=http%3A%2F%2Fexample.org%2Fresource HTTP/1.1 Host: example.com Connection: close Figure 3: Client HTTP GET against the Link Set Resource Figure 4 shows the response headers to the HTTP GET request of Figure 3. The links pertaining to the origin resource are provided Wilde & Van de Sompel Expires March 21, 2019 [Page 12] Internet-Draft Linkset September 2018 in the Link response header of the link set resource. As can be seen, in order to support an unambiguous determination of the link context of each link, the "anchor" attribute is always provided. Note that most, but not all, links have the origin resource as link context (anchor). HTTP/1.1 200 OK Date: Mon, 28 Nov 2016 14:40:02 GMT Server: Apache-Coyote/1.1 Link: ; rel="author" ; type="application/rdf+xml" ; anchor="http://example.org/resource1", ; rel="author" ; type="application/rdf+xml" ; anchor="http://example.org/resource1", ; rel="item" ; type="application/pdf" ; anchor="http://example.org/resource1", ; rel="item" ; type="text/html" ; anchor="http://example.org/resource1", ; rel="related" ; type="application/pdf" ; anchor="http://example.org/resource1/items/AF48EF.pdf" Content-Type: text/html Content-Length: 3018 Figure 4: Response to HTTP GET against the Link Set Resource 6.2. Links Provided in the Body of the Link Set Resource, Link Set Serialized as application/linkset+json Figure 5 is an example of a client issuing an HTTP head request against origin resource http://example.org/article?id=10.1371/ journal.pone.0167475 HEAD article?id=10.1371/journal.pone.0167475 HTTP/1.1 Host: example.org Connection: close Figure 5: Client HTTP HEAD Request Wilde & Van de Sompel Expires March 21, 2019 [Page 13] Internet-Draft Linkset September 2018 Figure 6 shows the response to the HEAD request of Figure 5. The response contains a Link header with a link that has the "linkset" relation type. It indicates that links pertaining to the origin resource are provided by link set resource http://example.com/links/10.1371/journal.pone.0167475, which provides a representation with media type application/linkset+json. HTTP/1.1 200 OK Date: Mon, 28 Nov 2016 14:37:51 GMT Server: Apache-Coyote/1.1 Link: ; rel="linkset" ; type="application/linkset+json" Content-Length: 236 Content-Type: text/html;charset=utf-8 Connection: close Figure 6: Response to HTTP HEAD on Origin Resource In this example, the URI of the linkset resource does not directly represent the URI of the origin resource anymore. There still is an association possible through the use of a URI pattern that is includes identifying information. But as in the example above, the URI of the link set resource is opaque to the client that simply accesses the URI to retrieve the link set resource. Figure 7 shows the client issuing an HTTP GET request against the link set resource provided in Figure 6. GET /links/10.1371/journal.pone.0167475 HTTP/1.1 Host: example.com Accept: application/linkset+json Connection: close Figure 7: Client HTTP GET against the Link Set Resource Figure 8 shows the response headers to the HTTP GET request of Figure 7. The links pertaining to the origin resource are provided in the response body of the link set resource and are serialized according to the media type application/linkset+json. Wilde & Van de Sompel Expires March 21, 2019 [Page 14] Internet-Draft Linkset September 2018 HTTP/1.1 200 OK Date: Mon, 28 Nov 2016 14:40:02 GMT Server: Apache-Coyote/1.1 Content-Type: application/linkset+json Content-Length: 794 [{"href":"http://authors.example.net/johndoe", "anchor":"http://example.org/article?id=10.1371/journal.pone.0167475", "rel":["author"],"type":"application/rdf+xml"}, {"href":"http://authors.example.net/janedoe", "anchor":"http://example.org/article?id=10.1371/journal.pone.0167475", "rel":["author"],"type":"application/rdf+xml"}, {"href":"http://example.org/resource1/items/AF48EF.pdf", "anchor":"http://example.org/article?id=10.1371/journal.pone.0167475", "rel":["item"],"type":"text/html"}, {"href":"http://example.org/resource1/items/CB63DA.html", "anchor":"http://example.org/article?id=10.1371/journal.pone.0167475", "rel":"[item"],"type":"application/pdf"}, {"href":"http://example.net/resource41/", "anchor":"http://example.org/resource1/items/AF48EF.pdf", "rel":["related"],"type":"application/pdf"}] Figure 8: Response to HTTP GET against the Link Set Resource If Figure 6 would have provided a link to a link set with media type application/linkset, and if the client would have requested that link set, then the body of the response would have been similar to Figure 8. But it would have had application/linkset as Content-Type, the payload of the HTTP Link header of Figure 4 as body, and an accordingly adjusted value for Content-Length. 7. Implementation Status Note to RFC Editor: Please remove this section before publication. This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in RFC 6982 [RFC6982]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. Wilde & Van de Sompel Expires March 21, 2019 [Page 15] Internet-Draft Linkset September 2018 According to RFC 6982, "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". 7.1. Open Journal Systems (OJS) Open Journal Systems (OJS) is an open-source software for the management of peer-reviewed academic journals, and is created by the Public Knowledge Project (PKP), released under the GNU General Public License. Open Journal Systems (OJS) is a journal management and publishing system that has been developed by PKP through its federally funded efforts to expand and improve access to research. The OJS platform has implemented linkset support as an alternative way to provide links when there are more than a configured limit (they consider using about 10 as a good default, for testing purpose it is currently set to 8). 8. IANA Considerations 8.1. Link Relation Type: linkset The link relation type below has been registered by IANA per Section 6.2.1 of Web Linking [RFC8288]: Relation Name: linkset Description: The Target IRI of a link with the "linkset" relation type provides a set of links that pertain to the Context IRI of the link. Reference: [[ This document ]] 8.2. Media Type: application/linkset 8.2.1. IANA Considerations The Internet media type [RFC6838] for a natively encoded link set is application/linkset. Type name: application Subtype name: linkset Required parameters: none Wilde & Van de Sompel Expires March 21, 2019 [Page 16] Internet-Draft Linkset September 2018 Optional parameters: none Encoding considerations: ... Security considerations: ... Interoperability considerations: ... Published specification: [[ This document ]] Applications that use this media type: ... Additional information: Magic number(s): N/A File extension(s): This media type does not propose a specific extension. Macintosh file type code(s): TEXT Person & email address to contact for further information: Herbert Van de Sompel Intended usage: COMMON Restrictions on usage: none Author: Herbert Van de Sompel Change controller: IETF 8.3. Media Type: application/linkset+json The Internet media type [RFC6838] for a JSON-encoded link set is application/linkset+json. Type name: application Subtype name: linkset+json Required parameters: none Optional parameters: none Encoding considerations: ... Security considerations: ... Wilde & Van de Sompel Expires March 21, 2019 [Page 17] Internet-Draft Linkset September 2018 Interoperability considerations: ... Published specification: [[ This document ]] Applications that use this media type: ... Additional information: Magic number(s): N/A File extension(s): JSON documents often use ".json" as the file extension, and this media type does not propose a specific extension other than this generic one. Macintosh file type code(s): TEXT Person & email address to contact for further information: Herbert Van de Sompel Intended usage: COMMON Restrictions on usage: none Author: Herbert Van de Sompel Change controller: IETF 9. Security Considerations ... 10. 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, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, September 2009, . Wilde & Van de Sompel Expires March 21, 2019 [Page 18] Internet-Draft Linkset September 2018 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, . [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, DOI 10.17487/RFC6982, July 2013, . [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014, . [RFC8187] Reschke, J., "Indicating Character Encoding and Language for HTTP Header Field Parameters", RFC 8187, DOI 10.17487/RFC8187, September 2017, . [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, . [RFC8288] Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017, . [W3C.REC-html401-19991224] Rivoal, F., "Media Queries", World Wide Web Consortium Recommendation REC-css3-mediaqueries-20120619, June 2012. Authors' Addresses Erik Wilde CA Technologies Email: erik.wilde@dret.net URI: http://dret.net/netdret/ Wilde & Van de Sompel Expires March 21, 2019 [Page 19] Internet-Draft Linkset September 2018 Herbert Van de Sompel Los Alamos National Laboratory Email: herbertv@lanl.gov URI: http://public.lanl.gov/herbertv/ Wilde & Van de Sompel Expires March 21, 2019 [Page 20]