draft-ietf-httpapi-linkset-02.txt   draft-ietf-httpapi-linkset-03.txt 
Network Working Group E. Wilde Network Working Group E. Wilde
Internet-Draft Axway Internet-Draft Axway
Intended status: Informational H. Van de Sompel Intended status: Informational H. Van de Sompel
Expires: December 6, 2021 Data Archiving and Networked Services Expires: 5 January 2022 Data Archiving and Networked Services
June 4, 2021 4 July 2021
Linkset: Media Types and a Link Relation Type for Link Sets Linkset: Media Types and a Link Relation Type for Link Sets
draft-ietf-httpapi-linkset-02 draft-ietf-httpapi-linkset-03
Abstract Abstract
This specification defines two document formats and respective media This specification defines two document formats and respective media
types for representing sets of links as stand-alone resources. One types for representing sets of links as stand-alone resources. One
format is JSON-based, the other aligned with the format for format is JSON-based, the other aligned with the format for
representing links in the HTTP "Link" header field. This representing links in the HTTP "Link" header field. This
specification also introduces a link relation type to support specification also introduces a link relation type to support
discovery of sets of links. discovery of sets of links.
Note to Readers Note to Readers
Please discuss this draft on the "Building Blocks for HTTP APIs" Please discuss this draft on the "Building Blocks for HTTP APIs"
mailing list (<https://www.ietf.org/mailman/listinfo/httpapi>). mailing list (https://www.ietf.org/mailman/listinfo/httpapi).
Online access to all versions and files is available on GitHub Online access to all versions and files is available on GitHub
(<https://github.com/ietf-wg-httpapi/linkset>). (https://github.com/ietf-wg-httpapi/linkset).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 6, 2021. This Internet-Draft will expire on 5 January 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Third-Party Links . . . . . . . . . . . . . . . . . . . . 4 3.1. Third-Party Links . . . . . . . . . . . . . . . . . . . . 4
3.2. Challenges Writing to HTTP Link Header Field . . . . . . 5 3.2. Challenges Writing to HTTP Link Header Field . . . . . . 4
3.3. Large Number of Links . . . . . . . . . . . . . . . . . . 5 3.3. Large Number of Links . . . . . . . . . . . . . . . . . . 5
4. Document Formats for Sets of Links . . . . . . . . . . . . . 5 4. Document Formats for Sets of Links . . . . . . . . . . . . . 5
4.1. HTTP Link Document Format: application/linkset . . . . . 6 4.1. HTTP Link Document Format: application/linkset . . . . . 6
4.2. JSON Document Format: application/linkset+json . . . . . 6 4.2. JSON Document Format: application/linkset+json . . . . . 6
4.2.1. Set of Links . . . . . . . . . . . . . . . . . . . . 7 4.2.1. Set of Links . . . . . . . . . . . . . . . . . . . . 7
4.2.2. Link Context Object . . . . . . . . . . . . . . . . . 8 4.2.2. Link Context Object . . . . . . . . . . . . . . . . . 7
4.2.3. Link Target Object . . . . . . . . . . . . . . . . . 8 4.2.3. Link Target Object . . . . . . . . . . . . . . . . . 8
4.2.4. Link Target Attributes . . . . . . . . . . . . . . . 10 4.2.4. Link Target Attributes . . . . . . . . . . . . . . . 10
4.2.5. JSON Extensibility . . . . . . . . . . . . . . . . . 14 4.2.5. JSON Extensibility . . . . . . . . . . . . . . . . . 14
5. The "profile" attribute for media types to Represent Sets of 5. The "profile" attribute for media types to Represent Sets of
Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Links . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6. The "linkset" Relation Type for Linking to a Set of Links . . 15 6. The "linkset" Relation Type for Linking to a Set of Links . . 15
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 15 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Set of Links Provided as application/linkset . . . . . . 15 7.1. Set of Links Provided as application/linkset . . . . . . 16
7.2. Set of Links Provided as application/linkset+json . . . . 17 7.2. Set of Links Provided as application/linkset+json . . . . 17
7.3. Discovering a Link Set via the "linkset" Link Relation 7.3. Discovering a Link Set via the "linkset" Link Relation
Type . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Type . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 20 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8.1. GS1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1. Link Relation Type: linkset . . . . . . . . . . . . . . . 20
8.2. FAIR Signposting Profile . . . . . . . . . . . . . . . . 21 8.2. Media Type: application/linkset . . . . . . . . . . . . . 20
8.3. Open Journal Systems (OJS) . . . . . . . . . . . . . . . 21 8.3. Media Type: application/linkset+json . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9.1. Link Relation Type: linkset . . . . . . . . . . . . . . . 21 10. Normative References . . . . . . . . . . . . . . . . . . . . 23
9.2. Media Type: application/linkset . . . . . . . . . . . . . 22 11. Informative References . . . . . . . . . . . . . . . . . . . 24
9.3. Media Type: application/linkset+json . . . . . . . . . . 23 Appendix A. JSON-LD Context . . . . . . . . . . . . . . . . . . 25
10. Security Considerations . . . . . . . . . . . . . . . . . . . 24 Appendix B. Implementation Status . . . . . . . . . . . . . . . 30
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 B.1. GS1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
11.1. Normative References . . . . . . . . . . . . . . . . . . 24 B.2. FAIR Signposting Profile . . . . . . . . . . . . . . . . 31
11.2. Informative References . . . . . . . . . . . . . . . . . 26 B.3. Open Journal Systems (OJS) . . . . . . . . . . . . . . . 31
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 27 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 31
Appendix B. JSON-LD Context . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
Resources on the Web often use typed Web Links [RFC8288], either Resources on the Web often use typed Web Links [RFC8288], either
embedded in resource representations, for example using the <link> embedded in resource representations, for example using the <link>
element for HTML documents, or conveyed in the HTTP "Link" header for element for HTML documents, or conveyed in the HTTP "Link" header
documents of any media type. In some cases, however, providing links field for documents of any media type. In some cases, however,
in this manner is impractical or impossible and delivering a set of providing links in this manner is impractical or impossible and
links as a stand-alone document is preferable. delivering a set of links as a stand-alone document is preferable.
Therefore, this specification defines two document formats and Therefore, this specification defines two document formats and
associated media types to represent sets of links. It also defines associated media types to represent sets of links. It also defines
the "linkset" relation type that supports discovery of any resource the "linkset" relation type that supports discovery of any resource
that conveys a set of links as a stand-alone document. that conveys a set of links as a stand-alone document.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This specification uses the terms "link context" and "link target" as This specification uses the terms "link context" and "link target" as
defined in [RFC8288]. These terms respectively correspond with defined in [RFC8288].
"Context IRI" and "Target IRI" as used in [RFC5988]. Although
defined as IRIs, in common scenarios they are also URIs.
In the examples provided in this document, links in the HTTP "Link" In the examples provided in this document, links in the HTTP "Link"
header are shown on separate lines in order to improve readability. header field are shown on separate lines in order to improve
Note, however, that as per Section 3.2 of [RFC7230], line breaks are readability. Note, however, that as per Section 5.5 of
not allowed in values for HTTP headers; only whitespaces and tabs are [I-D.ietf-httpbis-semantics], line breaks are deprecated in values
supported as seperators. for HTTP fields; only whitespaces and tabs are supported as
separators.
3. Scenarios 3. Scenarios
The following sections outline scenarios in which providing links by The following sections outline scenarios in which providing links by
means of a standalone document instead of in an HTTP "Link" header means of a standalone document instead of in an HTTP "Link" header
field or as links embedded in the resource representation is field or as links embedded in the resource representation is
advantageous or necessary. advantageous or necessary.
For all scenarios, links could be provided by means of a stand-alone For all scenarios, links could be provided by means of a stand-alone
document that is formatted according to the JSON-based serialization, document that is formatted according to the JSON-based serialization,
the serialization aligned with the HTTP "Link" header format, or the serialization aligned with the HTTP "Link" field format, or both.
both. The former serialization is motivated by the widespread use of The former serialization is motivated by the widespread use of JSON
JSON and related tools, which suggests that handling sets of links and related tools, which suggests that handling sets of links
expressed as JSON documents should be attractive to developers. The expressed as JSON documents should be attractive to developers. The
latter serialization is provided for compatibility with the existing latter serialization is provided for compatibility with the existing
serialization used in the HTTP "Link" header and to allow reuse of serialization used in the HTTP "Link" field and to allow reuse of
tools created to handle it. tools created to handle it.
It is important to keep in mind that when providing links by means of It is important to keep in mind that when providing links by means of
a standalone representation, other links can still be provided using a standalone representation, other links can still be provided using
other approaches, i.e. it is possible combine various mechanisms to other approaches, i.e. it is possible combine various mechanisms to
convey links. convey links.
3.1. Third-Party Links 3.1. Third-Party Links
In some cases it is useful that links pertaining to a resource are In some cases it is useful that links pertaining to a resource are
provided by a server other than the one that hosts the resource. For provided by a server other than the one that hosts the resource. For
example, this allows: example, this allows:
o Providing links in which the resource is involved not just as link * Providing links in which the resource is involved not just as link
context but also as link target. context but also as link target.
o Providing links pertaining to the resource that the server hosting * Providing links pertaining to the resource that the server hosting
that resource is not aware of. that resource is not aware of.
o External management of links pertaining to the resource in a * External management of links pertaining to the resource in a
special-purpose link management service. special-purpose link management service.
In such cases, links pertaining to a resource can be provided by In such cases, links pertaining to a resource can be provided by
another, specific resource. That specific resource may be managed by another, specific resource. That specific resource may be managed by
the same or by another custodian as the resource to which the links the same or by another custodian as the resource to which the links
pertain. For clients intent on consuming links provided in that pertain. For clients intent on consuming links provided in that
manner, it would be beneficial if the following conditions were met: manner, it would be beneficial if the following conditions were met:
o Links are provided in a document that uses a well-defined media * Links are provided in a document that uses a well-defined media
type. type.
o The resource to which the provided links pertain is able to link * The resource to which the provided links pertain is able to link
to the resource that provides these links using a well-known link to the resource that provides these links using a well-known link
relation type. relation type.
These requirements are addressed in this specification through the These requirements are addressed in this specification through the
definition of two media types and a link relation type, respectively. definition of two media types and a link relation type, respectively.
3.2. Challenges Writing to HTTP Link Header Field 3.2. Challenges Writing to HTTP Link Header Field
In some cases, it is not straightforward to write links to the HTTP In some cases, it is not straightforward to write links to the HTTP
"Link" header field from an application. This can, for example, be "Link" header field from an application. This can, for example, be
the case because not all required link information is available to the case because not all required link information is available to
the application or because the application does not have the the application or because the application does not have the
capability to directly write HTTP headers. In such cases, providing capability to directly write HTTP fields. In such cases, providing
links by means of a standalone document can be a solution. Making links by means of a standalone document can be a solution. Making
the resource that provides these links discoverable can be achieved the resource that provides these links discoverable can be achieved
by means of a typed link. by means of a typed link.
3.3. Large Number of Links 3.3. Large Number of Links
When conveying links in an HTTP "Link" header field, it is possible When conveying links in an HTTP "Link" header field, it is possible
for the size of the HTTP response header to become unpredictable. for the size of the HTTP response fields to become unpredictable.
This can be the case when links are determined dynamically dependent This can be the case when links are determined dynamically dependent
on a range of contextual factors. It is possible to statically on a range of contextual factors. It is possible to statically
configure a web server to correctly handle large HTTP response configure a web server to correctly handle large HTTP response fields
headers by specifying an upper bound for their size. But when the by specifying an upper bound for their size. But when the number of
number of links is unpredictable, estimating a reliable upper bound links is unpredictable, estimating a reliable upper bound is
is challenging. challenging.
HTTP [RFC7231] defines error codes related to excess communication by Section 15 of HTTP [I-D.ietf-httpbis-semantics] defines error codes
the user agent ("413 Request Entity Too Large" and "414 Request-URI related to excess communication by the user agent ("413 Request
Too Long"), but no specific error codes are defined to indicate that Entity Too Large" and "414 Request-URI Too Long"), but no specific
response header content exceeds the upper bound that can be handled error codes are defined to indicate that response field content
by the server, and thus it has been truncated. As a result, exceeds the upper bound that can be handled by the server, and thus
applications take counter measures aimed at controlling the size of it has been truncated. As a result, applications take counter
the HTTP "Link" header field, for example by limiting the links they measures aimed at controlling the size of the HTTP "Link" header
provide to those with select relation types, thereby limiting the field, for example by limiting the links they provide to those with
value of the HTTP "Link" header field to clients. Providing links by select relation types, thereby limiting the value of the HTTP "Link"
means of a standalone document overcomes challenges related to the header field to clients. Providing links by means of a standalone
unpredictable nature of the size of HTTP "Link" header fields. document overcomes challenges related to the unpredictable nature of
the size of HTTP "Link" header fields.
4. Document Formats for Sets of Links 4. Document Formats for Sets of Links
This section specifies two document formats to convey a set of links. This section specifies two document formats to convey a set of links.
Both are based on the abstract model specified in Section 2 of Web Both are based on the abstract model specified in Section 2 of Web
Linking [RFC8288] that defines a link as consisting of a "link Linking [RFC8288] that defines a link as consisting of a "link
context", a "link relation type", a "link target", and optional context", a "link relation type", a "link target", and optional
"target attributes": "target attributes":
o The format defined in Section 4.1 is identical to the payload of * The format defined in Section 4.1 is identical to the payload of
the HTTP "Link" header field as specified in Web Linking the HTTP "Link" header field as specified in Web Linking Section 3
[RFC8288]. of [RFC8288].
o The format defined in Section 4.2 is based on JSON [RFC8259]. * The format defined in Section 4.2 is based on JSON [RFC8259].
Note that [RFC8288] deprecates the "rev" construct that was provided Note that Section 3.3 of [RFC8288] deprecates the "rev" construct
by [RFC5988] as a means to express links with a directionality that that was provided by [RFC5988] as a means to express links with a
is the inverse of direct links that use the "rel" construct. In both directionality that is the inverse of direct links that use the "rel"
serializations for link sets defined here, inverse links SHOULD be construct. In both serializations for link sets defined here,
represented as direct links using the "rel" construct and by inverse links SHOULD be represented as direct links using the "rel"
switching the position of the resources involved in the link. construct and by switching the position of the resources involved in
the link.
4.1. HTTP Link Document Format: application/linkset 4.1. HTTP Link Document Format: application/linkset
This document format is identical to the payload of the HTTP "Link" This document format is identical to the payload of the HTTP "Link"
header field as defined in Section 3 of [RFC8288], more specifically header field as defined in Section 3 of [RFC8288], more specifically
by its ABNF production rule for "Link" and subsequent ones. Whereas by its ABNF production rule for "Link" and subsequent ones. The use
the HTTP "Link" Header field depends on HTTP and hence on [RFC0822] of non-ASCII characters in the payload of the HTTP "Link" Header
for its encoding, the format specified here is encoded as UTF-8 field is not interoperable.
[RFC3629].
The assigned media type for this format is "application/linkset". The assigned media type for this format is "application/linkset".
In order to support use cases where "application/linkset" documents In order to support use cases where "application/linkset" documents
are re-used outside the context of an HTTP interaction, it is are re-used outside the context of an HTTP interaction, it is
RECOMMENDED to make them self-contained by adhering to the following RECOMMENDED to make them self-contained by adhering to the following
guidelines: guidelines:
o For every link provided in the set of links, explicitly provide * For every link provided in the set of links, explicitly provide
the link context using the "anchor" attribute. the link context using the "anchor" attribute.
o For link context ("anchor" attribute) and link target ("href" * For link context ("anchor" attribute) and link target ("href"
attribute), use absolute URIs (as defined in Section 4.3 of attribute), use URI References that are not relative references
[RFC3986]). (as defined in Section 4.1 of [RFC3986]).
If these recommendations are not followed, interpretation of links in If these recommendations are not followed, interpretation of links in
"application/linkset" documents will depend on which URI is used as "application/linkset" documents will depend on which URI is used as
context. context.
It should be noted that the "application/linkset" format specified It should be noted that the "application/linkset" format specified
here is different than the "application/link-format" format specified here is different than the "application/link-format" format specified
in [RFC6690] in that the former fully matches the payload of the HTTP in [RFC6690] in that the former fully matches the payload of the HTTP
"Link" header as defined in Section 3 of [RFC8288], whereas the "Link" header field as defined in Section 3 of [RFC8288], whereas the
latter introduces constraints on that definition to meet requirements latter introduces constraints on that definition to meet requirements
for Constrained RESTful Environments. for Constrained RESTful Environments.
4.2. JSON Document Format: application/linkset+json 4.2. JSON Document Format: application/linkset+json
This document format uses JSON [RFC8259] as the syntax to represent a This document format uses JSON [RFC8259] as the syntax to represent a
set of links. The set of links follows the abstract model defined by set of links. The set of links follows the abstract model defined by
Web Linking [RFC8288]. Web Linking Section 2 of [RFC8288].
The assigned media type for this format is "application/ The assigned media type for this format is "application/
linkset+json". linkset+json".
In order to support use cases where "application/linkset+json" In order to support use cases where "application/linkset+json"
documents are re-used outside the context of an HTTP interaction, it documents are re-used outside the context of an HTTP interaction, it
is RECOMMENDED to make them self-contained by adhering to the is RECOMMENDED to make them self-contained by adhering to the
following guidelines: following guidelines:
o For every link provided in the set of links, explicitly provide * For every link provided in the set of links, explicitly provide
the link context using the "anchor" member. the link context using the "anchor" member.
o For link context ("anchor" member) and link target ("href" * For link context ("anchor" member) and link target ("href"
member), use absolute URIs (as defined in Section 4.3 of member), use URI References that are not relative references (as
[RFC3986]). defined in Section 4.1 of [RFC3986]).
If these recommendations are not followed, interpretation of If these recommendations are not followed, interpretation of
"application/linkset+json" will depend on which URI is used as "application/linkset+json" will depend on which URI is used as
context URI. context URI.
The "application/linkset+json" serialization is designed such that it The "application/linkset+json" serialization is designed such that it
can directly be used as the content of a JSON-LD serialization by can directly be used as the content of a JSON-LD serialization by
adding an appropriate context. Appendix B shows an example of a adding an appropriate context. Appendix A shows an example of a
possible context that, when added to a JSON serialization, allows it possible context that, when added to a JSON serialization, allows it
to be interpreted as RDF. to be interpreted as RDF.
4.2.1. Set of Links 4.2.1. Set of Links
In the JSON representation of a set of links: In the JSON representation of a set of links:
o A set of links MUST be represented as a JSON object which MUST * A set of links MUST be represented as a JSON object which MUST
have "linkset" as its sole member. have "linkset" as its sole member.
o The "linkset" member is an array in which a distinct JSON object - * The "linkset" member is an array in which a distinct JSON object -
the "link context object" (see Section 4.2.2) - MUST be used to the "link context object" (see Section 4.2.2) - MUST be used to
represent links that have the same link context. represent links that have the same link context.
o If necessary, the "linkset" member MAY contain information in * Even if there is only one link context object, it MUST be wrapped
addition to link context objects, in which case that information
MUST NOT change the semantics of the links provided by those link
context objects.
o Even if there is only one link context object, it MUST be wrapped
in an array. Members other than link context objects MUST NOT be in an array. Members other than link context objects MUST NOT be
included in this array. included in this array.
4.2.2. Link Context Object 4.2.2. Link Context Object
In the JSON representation one or more links that have the same link In the JSON representation one or more links that have the same link
context are represented by a JSON object, the link context object. A context are represented by a JSON object, the link context object. A
link context object adheres to the following rules: link context object adheres to the following rules:
o Each link context object MAY have an "anchor" member with a value * Each link context object MAY have an "anchor" member with a value
that represents the link context. If present, this value SHOULD that represents the link context. If present, this value MUST be
be an absolute URI as defined in Section 4.3 of [RFC3986]. Cases a URI Reference and SHOULD NOT be a relative reference as per
where the anchor member is present, but no value is provided for Section 4.1 of [RFC3986].
it (i.e. the resource providing the set of links is the link
context for each link in the link context object) MUST be handled
by providing an "anchor" member with empty string ("anchor": "").
o For each distinct relation type that the link context has with * For each distinct relation type that the link context has with
link targets, a link context object MUST have an additional link targets, a link context object MUST have an additional
member. This member is an array in which a distinct JSON object - member. This member is an array in which a distinct JSON object -
the "link target object" (see Section 4.2.3) - MUST be used for the "link target object" (see Section 4.2.3) - MUST be used for
each link target for which the relationship with the link context each link target for which the relationship with the link context
(value of the encompassing anchor member) applies. The name of (value of the encompassing anchor member) applies. The name of
this member expresses the relation type of the link as follows: this member expresses the relation type of the link as follows:
o - For registered relation types (Section 2.1.1 of [RFC8288]), the
name of this member is the registered name of the relation
* For registered relation types [RFC8288], the name of this type.
member is the registered name of the relation type.
* For extension relation types [RFC8288], the name of this member - For extension relation types (Section 2.1.2 of [RFC8288]), the
is the URI that uniquely represents the relation type. name of this member is the URI that uniquely represents the
relation type.
o Even if there is only one link target object it MUST be wrapped in * Even if there is only one link target object it MUST be wrapped in
an array. Members other than link target objects MUST NOT be an array. Members other than link target objects MUST NOT be
included in this array. included in this array.
4.2.3. Link Target Object 4.2.3. Link Target Object
In the JSON representation a link target is represented by a JSON In the JSON representation a link target is represented by a JSON
object, the link target object. A link target object adheres to the object, the link target object. A link target object adheres to the
following rules: following rules:
o Each link target object MUST have an "href" member with a value * Each link target object MUST have an "href" member with a value
that represents the link target. This value SHOULD be an absolute that represents the link target. This value MUST be a URI
URI as defined in Section 4.3 of [RFC3986]. Cases where the href Reference and SHOULD NOT be a relative reference as per
member is present, but no value is provided for it (i.e. the Section 4.1 of [RFC3986]. Cases where the href member is present,
resource providing the set of links is the target of the link in but no value is provided for it (i.e. the resource providing the
the link target object) MUST be handled by providing an "href" set of links is the target of the link in the link target object)
member with an empty string ("href": ""). MUST be handled by providing an "href" member with an empty string
("href": "").
o In many cases, a link target is further qualified by target * In many cases, a link target is further qualified by target
attributes. Various types of attributes exist and they are attributes. Various types of attributes exist and they are
conveyed as additional members of the link target object as conveyed as additional members of the link target object as
detailed in Section 4.2.4. detailed in Section 4.2.4.
The following example of a JSON-serialized set of links represents The following example of a JSON-serialized set of links represents
one link with its core components: link context, link relation type, one link with its core components: link context, link relation type,
and link target. and link target.
{ {
"linkset": "linkset":
[ [
{ "anchor": "http://example.net/bar", { "anchor": "http://example.net/bar",
"next": [ "next": [
{"href": "http://example.com/foo"} {"href": "http://example.com/foo"}
] ]
} }
] ]
} }
Figure 1
The following example of a JSON-serialized set of links represents The following example of a JSON-serialized set of links represents
two links that share link context and relation type but have two links that share link context and relation type but have
different link targets. different link targets.
{ {
"linkset": "linkset":
[ [
{ "anchor": "http://example.net/bar", { "anchor": "http://example.net/bar",
"item": [ "item": [
{"href": "http://example.com/foo1"}, {"href": "http://example.com/foo1"},
{"href": "http://example.com/foo2"} {"href": "http://example.com/foo2"}
] ]
} }
] ]
} }
Figure 2
The following example shows a set of links that represents two links, The following example shows a set of links that represents two links,
each with a different link context, link target, and relation type. each with a different link context, link target, and relation type.
One relation type is registered, the other is an extension relation One relation type is registered, the other is an extension relation
type. type.
{ {
"linkset": "linkset":
[ [
{ "anchor": "http://example.net/bar", { "anchor": "http://example.net/bar",
"next": [ "next": [
skipping to change at page 10, line 21 skipping to change at page 10, line 21
] ]
}, },
{ "anchor": "http://example.net/boo", { "anchor": "http://example.net/boo",
"http://example.com/relations/baz" : [ "http://example.com/relations/baz" : [
{"href": "http://example.com/foo2"} {"href": "http://example.com/foo2"}
] ]
} }
] ]
} }
Figure 3
4.2.4. Link Target Attributes 4.2.4. Link Target Attributes
A link may be further qualified by target attributes. Three types of A link may be further qualified by target attributes. Three types of
attributes exist: attributes exist:
o Attributes defined by the serialization of Web Linking [RFC8288]. * Attributes defined in Section 3.4.1 of Web Linking [RFC8288].
o Extension attributes defined and used by communities as allowed by * Extension attributes defined and used by communities as allowed by
[RFC8288]. Section 3.4.2 of [RFC8288].
o Internationalized versions of the "title" attribute defined by * Internationalized versions of the "title" attribute defined by
[RFC8288] and of extension attributes allowed by [RFC8288]. [RFC8288] and of extension attributes allowed by Section 3.4 of
[RFC8288].
The handling of these different types of attributes is described in The handling of these different types of attributes is described in
the sections below. the sections below.
4.2.4.1. Target Attributes Defined by Web Linking 4.2.4.1. Target Attributes Defined by Web Linking
RFC 8288 defines the following target attributes that may be used to Section 3.4.1 of [RFC8288] defines the following target attributes
annotate links: "hreflang", "media", "title", "title*", and "type"; that may be used to annotate links: "hreflang", "media", "title",
these target attributes follow different occurrence and value "title*", and "type"; these target attributes follow different
patterns. In the JSON representation, these attributes MUST be occurrence and value patterns. In the JSON representation, these
conveyed as additional members of the link target object as follows: attributes MUST be conveyed as additional members of the link target
object as follows:
o "hreflang": The optional and repeatable "hreflang" target * "hreflang": The optional and repeatable "hreflang" target
attribute MUST be represented by an array (even if there only is 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 one value to be represented), and each value in that array MUST be
a string - representing one value of the "hreflang" target a string - representing one value of the "hreflang" target
attribute for a link - which follows the same model as in the attribute for a link - which follows the same model as in the
[RFC8288] syntax. [RFC8288] syntax.
o "media": The optional and not repeatable "media" target attribute * "media": The optional and not repeatable "media" target attribute
MUST be represented by a "media" member in the link target object, MUST be represented by a "media" member in the link target object,
and its value MUST be a string that follows the same model as in and its value MUST be a string that follows the same model as in
the [RFC8288] syntax. the [RFC8288] syntax.
o "type": The optional and not repeatable "type" target attribute * "type": The optional and not repeatable "type" target attribute
MUST be represented by a "type" member in the link target object, MUST be represented by a "type" member in the link target object,
and its value MUST be a string that follows the same model as in and its value MUST be a string that follows the same model as in
the [RFC8288] syntax. the [RFC8288] syntax.
o "title": The optional and not repeatable "title" target attribute * "title": The optional and not repeatable "title" target attribute
MUST be represented by a "title" member in the link target object, MUST be represented by a "title" member in the link target object,
and its value MUST be a string that follows the same model as in and its value MUST be a string that follows the same model as in
the [RFC8288] syntax. the [RFC8288] syntax.
o "title*": The optional and not repeatable "title*" target * "title*": The optional and not repeatable "title*" target
attribute is motivated by character encoding and language issues attribute is motivated by character encoding and language issues
and follows the model defined in [RFC8187]. The details of the and follows the model defined in [RFC8187]. The details of the
JSON representation that applies to title* are described in JSON representation that applies to title* are described in
Section 4.2.4.2. Section 4.2.4.2.
The following example illustrates how the repeatable "hreflang" and The following example illustrates how the repeatable "hreflang" and
the not repeatable "type" target attributes are represented in a link the not repeatable "type" target attributes are represented in a link
target object. target object.
{ {
skipping to change at page 11, line 44 skipping to change at page 11, line 51
"next": [ "next": [
{"href": "http://example.com/foo", {"href": "http://example.com/foo",
"type": "text/html", "type": "text/html",
"hreflang": [ "en" , "de" ] "hreflang": [ "en" , "de" ]
} }
] ]
} }
] ]
} }
Figure 4
4.2.4.2. Internationalized Target Attributes 4.2.4.2. Internationalized Target Attributes
In addition to the target attributes described in Section 4.2.4.1, In addition to the target attributes described in Section 4.2.4.1,
[RFC8288] also supports attributes that follow the content model of Section 3.4 of [RFC8288] also supports attributes that follow the
[RFC8187]. In [RFC8288], these target attributes are recognizable by content model of [RFC8187]. In [RFC8288], these target attributes
the use of a trailing asterisk in the attribute name, such as are recognizable by the use of a trailing asterisk in the attribute
"title*". The content model of [RFC8187] uses a string-based name, such as "title*". The content model of [RFC8187] uses a
microsyntax that represents the character encoding, an optional string-based microsyntax that represents the character encoding, an
language tag, and the escaped attribute value encoded according to optional language tag, and the escaped attribute value encoded
the specified character encoding. according to the specified character encoding.
The JSON serialization for these target attributes MUST be as The JSON serialization for these target attributes MUST be as
follows: follows:
o An internationalized target attribute is represented as a member * An internationalized target attribute is represented as a member
of the link context object with the same name (including the *) of of the link context object with the same name (including the *) of
the attribute. the attribute.
o The character encoding information as prescribed by [RFC8187] is * The character encoding information as prescribed by [RFC8187] is
not preserved; instead, the content of the internationalized not preserved; instead, the content of the internationalized
attribute is represented in the character encoding used for the attribute is represented in the character encoding used for the
JSON set of links. JSON set of links.
o The value of the internationalized target attribute is an array * The value of the internationalized target attribute is an array
that contains one or more JSON objects. The name of one member of that contains one or more JSON objects. The name of one member of
such JSON object is "value" and its value is the actual content such JSON object is "value" and its value is the actual content
(in its unescaped version) of the internationalized target (in its unescaped version) of the internationalized target
attribute, i.e. the value of the attribute from which the encoding attribute, i.e. the value of the attribute from which the encoding
and language information are removed. The name of another, and language information are removed. The name of another,
optional, member of such JSON object is "language" and its value optional, member of such JSON object is "language" and its value
is the language tag [RFC5646] for the language in which the is the language tag [RFC5646] for the language in which the
attribute content is conveyed. attribute content is conveyed.
The following example illustrates how the "title*" target attribute The following example illustrates how the "title*" target attribute
defined by [RFC8288] is represented in a link target object. defined by Section 3.4.1 of [RFC8288] is represented in a link target
object.
{ {
"linkset": "linkset":
[ [
{ "anchor": "http://example.net/bar", { "anchor": "http://example.net/bar",
"next": [ "next": [
{"href": "http://example.com/foo", {"href": "http://example.com/foo",
"type": "text/html", "type": "text/html",
"hreflang": [ "en" , "de" ], "hreflang": [ "en" , "de" ],
"title": "Next chapter", "title": "Next chapter",
"title*": [ { "value": "nachstes Kapitel" , "title*": [ { "value": "nรคchstes Kapitel" ,
"language" : "de" } ] "language" : "de" } ]
} }
] ]
} }
] ]
} }
Figure 5
The above example assumes that the German title contains an umlaut The above example assumes that the German title contains an umlaut
character (in the native syntax it would be encoded as title*=UTF- character (in the native syntax it would be encoded as title*=UTF-
8'de'n%c3%a4chstes%20Kapitel), which gets encoded in its unescaped 8'de'n%c3%a4chstes%20Kapitel), which gets encoded in its unescaped
form in the JSON representation. This is not shown in the above form in the JSON representation. Implementations MUST properly
example due to the limitations of RFC publication. Implementations decode/encode internationalized target attributes that follow the
MUST properly decode/encode internationalized target attributes that model of [RFC8187] when transcoding between the "application/linkset"
follow the model of [RFC8187] when transcoding between the and the "application/linkset+json" formats.
"application/linkset" and the "application/linkset+json" formats.
4.2.4.3. Extension Target Attributes 4.2.4.3. Extension Target Attributes
Extension target attributes are attributes that are not defined by Extension target attributes are attributes that are not defined by
[RFC8288] (as listed in Section 4.2.4.1), but are nevertheless used Section 3.4.1 of [RFC8288] (as listed in Section 4.2.4.1), but are
to qualify links. They can be defined by communities in any way nevertheless used to qualify links. They can be defined by
deemed necessary, and it is up to them to make sure their usage is communities in any way deemed necessary, and it is up to them to make
understood by target applications. However, lacking standardization, sure their usage is understood by target applications. However,
there is no interoperable understanding of these extension lacking standardization, there is no interoperable understanding of
attributes. One important consequence is that their cardinality is these extension attributes. One important consequence is that their
unknown to generic applications. Therefore, in the JSON cardinality is unknown to generic applications. Therefore, in the
serialization, all extension target attributes are treated as JSON serialization, all extension target attributes are treated as
repeatable. repeatable.
The JSON serialization for these target attributes MUST be as The JSON serialization for these target attributes MUST be as
follows: follows:
o An extension target attribute is represented as a member of the * An extension target attribute is represented as a member of the
link context object with the same name of the attribute, including link context object with the same name of the attribute, including
the * if applicable. the * if applicable.
o The value of an extension attribute MUST be represented by an * The value of an extension attribute MUST be represented by an
array, even if there only is one value to be represented. array, even if there only is one value to be represented.
o If the extension target attribute does not have a name with a * If the extension target attribute does not have a name with a
trailing asterisk, then each value in that array MUST be a string trailing asterisk, then each value in that array MUST be a string
that represents one value of the attribute. that represents one value of the attribute.
o If the extension attribute has a name with a trailing asterisk (it * If the extension attribute has a name with a trailing asterisk (it
follows the content model of [RFC8187]), then each value in that follows the content model of [RFC8187]), then each value in that
array MUST be a JSON object. The value of each such JSON object array MUST be a JSON object. The value of each such JSON object
MUST be structured as described in Section 4.2.4.2. MUST be structured as described in Section 4.2.4.2.
The example shows a link target object with three extension target The example shows a link target object with three extension target
attributes. The value for each extension target attribute is an attributes. The value for each extension target attribute is an
array. The two first are regular extension target attributes, with array. The two first are regular extension target attributes, with
the first one ("foo") having only one value and the second one the first one ("foo") having only one value and the second one
("bar") having two. The last extension target attribute ("baz*") ("bar") having two. The last extension target attribute ("baz*")
follows the naming rule of [RFC8187] and therefore is encoded follows the naming rule of [RFC8187] and therefore is encoded
skipping to change at page 14, line 22 skipping to change at page 14, line 42
"foo": [ "foovalue" ], "foo": [ "foovalue" ],
"bar": [ "barone", "bartwo" ], "bar": [ "barone", "bartwo" ],
"baz*": [ { "value": "bazvalue" , "baz*": [ { "value": "bazvalue" ,
"language" : "en" } ] "language" : "en" } ]
} }
] ]
} }
] ]
} }
Figure 6
4.2.5. JSON Extensibility 4.2.5. JSON Extensibility
The extensibility of the JSON document format for representing a set The extensibility of the JSON document format for representing a set
of links is restricted to the extensibility provided by [RFC8288]. of links is restricted to the extensibility provided by [RFC8288].
The Web linking model provides for the use of extension target The Web linking model provides for the use of extension target
attributes as discussed in Section 4.2.4.3. Extensions based on the attributes as discussed in Section 4.2.4.3. Extensions based on the
JSON syntax MUST NOT be used, and MUST be ignored when found in a JSON syntax MUST NOT be used, and MUST be ignored when found in a
JSON linkset document. JSON linkset document.
This limitation of the JSON format allows to unambiguously round trip This limitation of the JSON format allows to unambiguously round trip
between links provided in the HTTP "Link" header, sets of links between links provided in the HTTP "Link" header field, sets of links
serialized according to the "application/linkset" format, and sets of serialized according to the "application/linkset" format, and sets of
links serialized according to the "application/linkset+json" format. links serialized according to the "application/linkset+json" format.
5. The "profile" attribute for media types to Represent Sets of Links 5. The "profile" attribute for media types to Represent Sets of Links
As a means to convey specific constraints or conventions (as per As a means to convey specific constraints or conventions (as per
[RFC6906]) that apply to a link set document, the "profile" attribute [RFC6906]) that apply to a link set document, the "profile" attribute
MAY be used in conjunction with the media types "application/linkset" MAY be used in conjunction with the media types "application/linkset"
and "application/linkset+json" detailed in Section 4.1 and and "application/linkset+json" detailed in Section 4.1 and
Section 4.2, respectively. For example, the attribute could be used Section 4.2, respectively. For example, the attribute could be used
skipping to change at page 15, line 9 skipping to change at page 15, line 30
The value of the "profile" attribute MUST be a non-empty list of The value of the "profile" attribute MUST be a non-empty list of
space-separated URIs, each of which identifies specific constraints space-separated URIs, each of which identifies specific constraints
or conventions that apply to the link set document. Profile URIs MAY or conventions that apply to the link set document. Profile URIs MAY
be registered in the IANA Profile URI Registry in the manner be registered in the IANA Profile URI Registry in the manner
specified by [RFC7284]. specified by [RFC7284].
The presence of a "profile" attribute in conjunction with the The presence of a "profile" attribute in conjunction with the
"application/linkset" and "application/linkset+json" media types does "application/linkset" and "application/linkset+json" media types does
not change the semantics of a link set. As such, clients with and not change the semantics of a link set. As such, clients with and
without knowledge of profile URIs can use the same representation. without knowledge of profile URIs can use the same representation.
The profile parameter MAY be used by clients to express their
preferences, and, if a client does so, a server SHOULD return a
document that honors the profiles it recognizes, and MUST ignore the
profiles which it does not recognize.
6. The "linkset" Relation Type for Linking to a Set of Links 6. The "linkset" Relation Type for Linking to a Set of Links
The target of a link with the "linkset" relation type provides a set The target of a link with the "linkset" relation type provides a set
of links, including links in which the resource that is the link of links, including links in which the resource that is the link
context participates. context participates.
A link with the "linkset" relation type MAY be provided in the header A link with the "linkset" relation type MAY be provided in the header
and/or the body of a resource's representation. It may also be field and/or the body of a resource's representation. It may also be
discovered by other means, such as through client-side information. discovered by other means, such as through client-side information.
A resource MAY provide more than one link with a "linkset" relation A resource MAY provide more than one link with a "linkset" relation
type. Multiple such links can refer to the same set of links type. Multiple such links can refer to the same set of links
expressed using different media types, or to different sets of links, expressed using different media types, or to different sets of links,
potentially provided by different third-party services. potentially provided by different third-party services.
A user agent that follows a "linkset" link MUST be aware that the set A user agent that follows a "linkset" link MUST be aware that the set
of links provided by the resource that is the target of the link can of links provided by the resource that is the target of the link can
contain links in which the resource that is the context of the link contain links in which the resource that is the context of the link
does not participate; it MAY decide to ignore those links. does not participate; it MAY decide to ignore those links.
A user agent that follows a "linkset" link and obtains links for A user agent that follows a "linkset" link and obtains links for
which anchors and targets are not expressed as absolute URIs MUST which anchors and targets are expressed as relative references (as
properly determine what the context is for these links; it SHOULD per Section 4.1 of [RFC3986]) MUST determine what the context is for
ignore links for which it is unable to unambiguously make that these links; it SHOULD ignore links for which it is unable to
determination. unambiguously make that determination.
7. Examples 7. Examples
Section 7.1 and Section 7.2 show examples whereby a set of links is Section 7.1 and Section 7.2 show examples whereby a set of links is
provided as "application/linkset" and "application/linkset+json" provided as "application/linkset" and "application/linkset+json"
documents, respectively. Section 7.3 illustrates the use of the documents, respectively. Section 7.3 illustrates the use of the
"linkset" link relation type to support discovery of sets of links. "linkset" link relation type to support discovery of sets of links.
7.1. Set of Links Provided as application/linkset 7.1. Set of Links Provided as application/linkset
Figure 1 shows a client issuing an HTTP GET request against resource Figure 7 shows a client issuing an HTTP GET request against resource
<https://example.org/links/resource1>. <https://example.org/links/resource1>.
GET /links/resource1 HTTP/1.1 GET /links/resource1 HTTP/1.1
Host: example.org Host: example.org
Connection: close
Figure 1: Client HTTP GET request Figure 7: Client HTTP GET request
Figure 2 shows the response to the GET request of Figure 1. The Figure 8 shows the response to the GET request of Figure 7. The
response contains a Content-Type header specifying that the media response contains a Content-Type header field specifying that the
type of the response is "application/linkset". A set of links, media type of the response is "application/linkset". A set of links,
revealing authorship and versioning related to resource revealing authorship and versioning related to resource
<https://example.org/resource1>, is provided in the response body. <https://example.org/resource1>, is provided in the response body.
The HTTP "Link" header indicates the availability of an alternate The HTTP "Link" header field indicates the availability of an
representation of the set of links using media type "application/ alternate representation of the set of links using media type
linkset+json". "application/linkset+json".
HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Mon, 12 Aug 2019 10:35:51 GMT Date: Mon, 12 Aug 2019 10:35:51 GMT
Server: Apache-Coyote/1.1 Server: Apache-Coyote/1.1
Content-Length: 1023 Content-Length: 1023
Content-Type: application/linkset; charset=UTF-8 Content-Type: application/linkset
Link: <https://example.org/links/resource1> ; rel="alternate" Link: <https://example.org/links/resource1>
; type="application/linkset+json" ; rel="alternate"
Connection: close ; type="application/linkset+json"
<https://authors.example.net/johndoe> <https://authors.example.net/johndoe>
; rel="author" ; rel="author"
; type="application/rdf+xml" ; type="application/rdf+xml"
; anchor="https://example.org/resource1", ; anchor="https://example.org/resource1",
<https://example.org/resource1?version=3> <https://example.org/resource1?version=3>
; rel="latest-version" ; rel="latest-version"
; type="text/html" ; type="text/html"
; anchor="https://example.org/resource1", ; anchor="https://example.org/resource1",
<https://example.org/resource1?version=2> <https://example.org/resource1?version=2>
; rel="predecessor-version" ; rel="predecessor-version"
skipping to change at page 17, line 43 skipping to change at page 17, line 44
; anchor="https://example.org/resource1", ; anchor="https://example.org/resource1",
<https://example.org/resource1?version=2> <https://example.org/resource1?version=2>
; rel="memento" ; rel="memento"
; type="text/html" ; type="text/html"
; datetime="Sun, 21 Jul 2019 12:22:04 GMT" ; datetime="Sun, 21 Jul 2019 12:22:04 GMT"
; anchor="https://example.org/resource1", ; anchor="https://example.org/resource1",
<https://authors.example.net/alice> <https://authors.example.net/alice>
; rel="author" ; rel="author"
; anchor="https://example.org/resource1#comment=1" ; anchor="https://example.org/resource1#comment=1"
Figure 2: Response to HTTP GET includes a set of links Figure 8: Response to HTTP GET includes a set of links
7.2. Set of Links Provided as application/linkset+json 7.2. Set of Links Provided as application/linkset+json
Figure 3 shows the client issuing an HTTP GET request against Figure 9 shows the client issuing an HTTP GET request against
<https://example.org/links/resource1>. In the request, the client <https://example.org/links/resource1>. In the request, the client
uses an "Accept" header to indicate it prefers a response in the uses an "Accept" header field to indicate it prefers a response in
"application/linkset+json" format. the "application/linkset+json" format.
GET links/resource1 HTTP/1.1 GET links/resource1 HTTP/1.1
Host: example.org Host: example.org
Accept: application/linkset+json Accept: application/linkset+json
Connection: close
Figure 3: Client HTTP GET request expressing preference for Figure 9: Client HTTP GET request expressing preference for
"application/linkset+json" response "application/ linkset+json" response
Figure 4 shows the response to the HTTP GET request of Figure 3. The Figure 10 shows the response to the HTTP GET request of Figure 9.
set of links is serialized according to the media type "application/ The set of links is serialized according to the media type
linkset+json". "application/linkset+json".
HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Mon, 12 Aug 2019 10:46:22 GMT Date: Mon, 12 Aug 2019 10:46:22 GMT
Server: Apache-Coyote/1.1 Server: Apache-Coyote/1.1
Content-Type: application/linkset+json Content-Type: application/linkset+json
Link: <https://example.org/links/resource1> ; rel="alternate" Link: <https://example.org/links/resource1>
; type="application/linkset" ; rel="alternate"
; type="application/linkset"
Content-Length: 1349 Content-Length: 1349
{ {
"linkset": [ "linkset": [
{ {
"anchor": "https://example.org/resource1", "anchor": "https://example.org/resource1",
"author": [ "author": [
{ {
"href": "https://authors.example.net/johndoe", "href": "https://authors.example.net/johndoe",
"type": "application/rdf+xml" "type": "application/rdf+xml"
} }
], ],
skipping to change at page 19, line 33 skipping to change at page 19, line 35
"anchor": "https://example.org/resource1#comment=1", "anchor": "https://example.org/resource1#comment=1",
"author": [ "author": [
{ {
"href": "https://authors.example.net/alice" "href": "https://authors.example.net/alice"
} }
] ]
} }
] ]
} }
Figure 4: Response to the client's request for the set of links Figure 10: Response to the client's request for the set of links
7.3. Discovering a Link Set via the "linkset" Link Relation Type 7.3. Discovering a Link Set via the "linkset" Link Relation Type
Figure 5 shows a client issuing an HTTP HEAD request against resource Figure 11 shows a client issuing an HTTP HEAD request against
<https://example.org/resource1>. resource <https://example.org/resource1>.
HEAD resource1 HTTP/1.1 HEAD resource1 HTTP/1.1
Host: example.org Host: example.org
Connection: close
Figure 5: Client HTTP HEAD request Figure 11: Client HTTP HEAD request
Figure 6 shows the response to the HEAD request of Figure 5. The Figure 12 shows the response to the HEAD request of Figure 11. The
response contains an HTTP "Link" header with a link that has the response contains an HTTP "Link" header field with a link that has
"linkset" relation type. It indicates that a set of links is the "linkset" relation type. It indicates that a set of links is
provided by resource <https://example.org/links/resource1>, which provided by resource <https://example.org/links/resource1>, which
provides a representation with media type "application/linkset+json". provides a representation with media type "application/linkset+json".
HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Mon, 12 Aug 2019 10:45:54 GMT Date: Mon, 12 Aug 2019 10:45:54 GMT
Server: Apache-Coyote/1.1 Server: Apache-Coyote/1.1
Link: <https://example.org/links/resource1> Link: <https://example.org/links/resource1>
; rel="linkset" ; rel="linkset"
; type="application/linkset+json" ; type="application/linkset+json"
Content-Length: 236 Content-Length: 236
Content-Type: text/html;charset=utf-8 Content-Type: text/html;charset=utf-8
Connection: close
Figure 6: Response to HTTP HEAD request Figure 12: Response to HTTP HEAD request
Section 7.2 shows a client obtaining a set of links by issuing an Section 7.2 shows a client obtaining a set of links by issuing an
HTTP GET on the target of the link with the "linkset" relation type, HTTP GET on the target of the link with the "linkset" relation type,
<https://example.org/links/resource1>. <https://example.org/links/resource1>.
8. Implementation Status 8. IANA Considerations
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.
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".
8.1. GS1
GS1 is a provider of barcodes (GS1 GTINs and EAN/UPC) for retail
products and manages an ecology of services and standards to leverage
them at a global scale. GS1 has indicated that it will implement
this "linkset" specification as a means to allow requesting and
representing links pertaining to products from various retailers.
Currently, the GS1 Digital Link specification makes an informative
reference to version 03 of the "linkset" I-D. GS1 expresses
confidence that this will become a normative reference in the next
iteration of that specification, likely to be ratified as a GS1
standard around February 2021.
8.2. FAIR Signposting Profile
The FAIR Signposting Profile is a community specification aimed at
improving machine navigation of scholarly objects on the web through
the use of typed web links pointing at e.g. web resources that are
part of a specific object, persistent identifiers for the object and
its authors, license information pertaining to the object. The
specification encourages the use of Linksets and initial
implementations are ongoing, for example, for the open source
Dataverse data repository platform that was initiated by Harvard
University and is meanwhile used by research institutions, worldwide.
8.3. 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).
9. IANA Considerations
9.1. Link Relation Type: linkset 8.1. Link Relation Type: linkset
The link relation type below has been registered by IANA per The link relation type below should be registered by IANA per
Section 6.2.1 of Web Linking [RFC8288]: Section 6.2.1 of Web Linking [RFC8288]:
Relation Name: linkset Relation Name: linkset
Description: The Target IRI of a link with the "linkset" relation Description: The link target of a link with the "linkset" relation
type provides a set of links, including links in which the Context type provides a set of links, including links in which the link
IRI of the link participates. context of the link participates.
Reference: [[ This document ]] Reference: [[ This document ]]
9.2. Media Type: application/linkset 8.2. Media Type: application/linkset
The Internet media type [RFC6838] for a natively encoded linkset is The Internet media type [RFC6838] for a natively encoded linkset is
application/linkset. application/linkset.
Type name: application Type name: application
Subtype name: linkset Subtype name: linkset
Required parameters: none Required parameters: none
skipping to change at page 22, line 17 skipping to change at page 21, line 4
The Internet media type [RFC6838] for a natively encoded linkset is The Internet media type [RFC6838] for a natively encoded linkset is
application/linkset. application/linkset.
Type name: application Type name: application
Subtype name: linkset Subtype name: linkset
Required parameters: none Required parameters: none
Optional parameters: profile Optional parameters: profile
Encoding considerations: Linksets are encoded according to the Encoding considerations: Linksets are encoded according to the
definition of [RFC8288]. The encoding of [RFC8288] is based on definition of [RFC8288]. The encoding of [RFC8288] is based on
the general encoding rules of [RFC7230], with the addition of the general encoding rules of [I-D.ietf-httpbis-semantics], with
allowing indicating character encoding and language for specific the addition of allowing indicating character encoding and
parameters as defined by [RFC8187]. language for specific parameters as defined by [RFC8187].
Security considerations: The security considerations of [[ This Security considerations: The security considerations of [[ This
document ]] apply. document ]] apply.
Interoperability considerations: The interoperability Interoperability considerations: N/A
considerations of [RFC7230] apply.
Published specification: [[ This document ]] Published specification: [[ This document ]]
Applications that use this media type: This media type is not Applications that use this media type: This media type is not
specific to any application, as it can be used by any application specific to any application, as it can be used by any application
that wants to interchange web links. that wants to interchange web links.
Additional information: Additional information:
Magic number(s): N/A Magic number(s): N/A
skipping to change at page 23, line 4 skipping to change at page 21, line 38
Macintosh file type code(s): TEXT Macintosh file type code(s): TEXT
Person & email address to contact for further information: Erik Person & email address to contact for further information: Erik
Wilde <erik.wilde@dret.net> Wilde <erik.wilde@dret.net>
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: none Restrictions on usage: none
Author: Erik Wilde <erik.wilde@dret.net> Author: Erik Wilde <erik.wilde@dret.net>
Change controller: IETF Change controller: IETF
9.3. Media Type: application/linkset+json 8.3. Media Type: application/linkset+json
The Internet media type [RFC6838] for a JSON-encoded linkset is The Internet media type [RFC6838] for a JSON-encoded linkset is
application/linkset+json. application/linkset+json.
Type name: application Type name: application
Subtype name: linkset+json Subtype name: linkset+json
Required parameters: none Required parameters: none
Optional parameters: profile Optional parameters: profile
Encoding considerations: The encoding considerations of [RFC8259] Encoding considerations: The encoding considerations of [RFC8259]
apply apply
Security considerations: The security considerations of [[ This Security considerations: The security considerations of [[ This
document ]] apply. document ]] apply.
Interoperability considerations: The interoperability Interoperability considerations: The interoperability
considerations of [RFC8259] apply. considerations of [RFC8259] apply.
skipping to change at page 24, line 4 skipping to change at page 22, line 39
Macintosh file type code(s): TEXT Macintosh file type code(s): TEXT
Person & email address to contact for further information: Erik Person & email address to contact for further information: Erik
Wilde <erik.wilde@dret.net> Wilde <erik.wilde@dret.net>
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: none Restrictions on usage: none
Author: Erik Wilde <erik.wilde@dret.net> Author: Erik Wilde <erik.wilde@dret.net>
Change controller: IETF Change controller: IETF
10. Security Considerations 9. Security Considerations
The security considerations of Web Linking [RFC8288] apply, as long The security considerations of Web Linking [RFC8288] apply, as long
as they are not specifically discussing the risks of exposing as they are not specifically discussing the risks of exposing
information in HTTP header fields. information in HTTP header fields.
In general, links may cause information leakage when they expose In general, links may cause information leakage when they expose
information (such as URIs) that can be sensitive or private. Links information (such as URIs) that can be sensitive or private. Links
may expose "hidden URIs" that are not supposed to be openly shared, may expose "hidden URIs" that are not supposed to be openly shared,
and may not be sufficiently protected. Ideally, none of the URIs and may not be sufficiently protected. Ideally, none of the URIs
exposed in links should be supposed to be "hidden"; instead, if these exposed in links should be supposed to be "hidden"; instead, if these
URIs are supposed to be limited to certain users, then technical URIs are supposed to be limited to certain users, then technical
measures should be put in place so that accidentally exposing them measures should be put in place so that accidentally exposing them
does not cause any harm. does not cause any harm.
For the specific mechanisms defined in this specification, two For the specific mechanisms defined in this specification, two
security considerations should be taken into account: security considerations should be taken into account:
o The Web Linking model always has an "implicit context", which is * The Web Linking model always has an "implicit context", which is
the resource of the HTTP interaction. This original context can the resource of the HTTP interaction. This original context can
be lost or can change when self-contained link representations are be lost or can change when self-contained link representations are
moved. Changing the context can change the interpretation of moved. Changing the context can change the interpretation of
links when they have no explicit anchor, or when they use relative links when they have no explicit anchor, or when they use relative
URIs. Applications may choose to ignore links that have no URIs. Applications may choose to ignore links that have no
explicit anchor or that use relative URIs when these are exchanged explicit anchor or that use relative URIs when these are exchanged
in stand-alone resources. in stand-alone resources.
o The model introduced in this specification supports "3rd party * The model introduced in this specification supports "3rd party
links", where one party can provide links that have another links", where one party can provide links that have another
party's resource as an anchor. Depending on the link semantics party's resource as an anchor. Depending on the link semantics
and the application context, it is important to verify that there and the application context, it is important to verify that there
is sufficient trust in that 3rd party to allow it to provide these is sufficient trust in that 3rd party to allow it to provide these
links. Applications may choose to treat 3rd party links links. Applications may choose to treat 3rd party links
differently than cases where a resource and the links for that differently than cases where a resource and the links for that
resource are provided by the same party. resource are provided by the same party.
11. References 10. Normative References
11.1. Normative References
[RFC0822] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET
TEXT MESSAGES", STD 11, RFC 822, DOI 10.17487/RFC0822,
August 1982, <https://www.rfc-editor.org/info/rfc822>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
2003, <https://www.rfc-editor.org/info/rfc3629>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
[RFC8187] Reschke, J., "Indicating Character Encoding and Language
for HTTP Header Field Parameters", RFC 8187,
DOI 10.17487/RFC8187, September 2017,
<https://www.rfc-editor.org/info/rfc8187>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
[RFC6906] Wilde, E., "The 'profile' Link Relation Type", RFC 6906, [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
DOI 10.17487/RFC6906, March 2013, Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
<https://www.rfc-editor.org/info/rfc6906>. September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, Code: The Implementation Status Section", RFC 6982,
DOI 10.17487/RFC6982, July 2013, DOI 10.17487/RFC6982, July 2013,
<https://www.rfc-editor.org/info/rfc6982>. <https://www.rfc-editor.org/info/rfc6982>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Protocol (HTTP/1.1): Message Syntax and Routing", Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
RFC 7230, DOI 10.17487/RFC7230, June 2014, <https://www.rfc-editor.org/info/rfc6690>.
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC6906] Wilde, E., "The 'profile' Link Relation Type", RFC 6906,
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC6906, March 2013,
DOI 10.17487/RFC7231, June 2014, <https://www.rfc-editor.org/info/rfc6906>.
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7284] Lanthaler, M., "The Profile URI Registry", RFC 7284, [RFC7284] Lanthaler, M., "The Profile URI Registry", RFC 7284,
DOI 10.17487/RFC7284, June 2014, DOI 10.17487/RFC7284, June 2014,
<https://www.rfc-editor.org/info/rfc7284>. <https://www.rfc-editor.org/info/rfc7284>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [I-D.ietf-httpbis-semantics]
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
May 2017, <https://www.rfc-editor.org/info/rfc8174>. Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-15, 30 March 2021,
[RFC8187] Reschke, J., "Indicating Character Encoding and Language <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
for HTTP Header Field Parameters", RFC 8187, semantics-15>.
DOI 10.17487/RFC8187, September 2017,
<https://www.rfc-editor.org/info/rfc8187>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288, 11. Informative References
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
11.2. Informative References [W3C.REC-json-ld-20140116]
Sporny, M., Kellogg, G., and M. Lanthaler, "JSON-LD 1.0",
World Wide Web Consortium Recommendation REC-json-ld-
20140116, 16 January 2014,
<https://www.w3.org/TR/2014/REC-json-ld-20140116>.
[RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
Syndication Format", RFC 4287, DOI 10.17487/RFC4287, Syndication Format", RFC 4287, DOI 10.17487/RFC4287,
December 2005, <https://www.rfc-editor.org/info/rfc4287>. December 2005, <https://www.rfc-editor.org/info/rfc4287>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, [RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010, DOI 10.17487/RFC5988, October 2010,
<https://www.rfc-editor.org/info/rfc5988>. <https://www.rfc-editor.org/info/rfc5988>.
[W3C.REC-json-ld-20140116] Appendix A. JSON-LD Context
Sporny, M., Kellogg, G., and M. Lanthaler, "JSON-LD 1.0",
World Wide Web Consortium Recommendation REC-json-ld-
20140116, January 2014,
<https://www.w3.org/TR/2014/REC-json-ld-20140116>.
11.3. URIs
[1] https://www.w3.org/TR/2014/REC-json-ld-20140116/#interpreting-
json-as-json-ld
[2] https://tools.ietf.org/html/rfc8288#appendix-A.2
Appendix A. Acknowledgements
Thanks for comments and suggestions provided by Phil Archer,
Dominique Guinard, Mark Nottingham, Stian Soiland-Reyes, and Sarven
Capadisli.
Appendix B. JSON-LD Context
A set of links rendered according to the JSON serialization defined A set of links rendered according to the JSON serialization defined
in Section 4.2 can be interpreted as RDF triples by adding a JSON-LD in Section 4.2 can be interpreted as RDF triples by adding a JSON-LD
context [W3C.REC-json-ld-20140116] that maps the JSON keys to context [W3C.REC-json-ld-20140116] that maps the JSON keys to
corresponding Linked Data terms. And, as per corresponding Linked Data terms. And, as per
[W3C.REC-json-ld-20140116] section 6.8 [1], when delivering a link [W3C.REC-json-ld-20140116] section 6.8 (https://www.w3.org/TR/2014/
set that is rendered according to the "application/linkset+json" REC-json-ld-20140116/#interpreting-json-as-json-ld), when delivering
media type to a user agent, a server can convey the availability of a link set that is rendered according to the "application/
such a JSON-LD context by using a link with the relation type linkset+json" media type to a user agent, a server can convey the
"http://www.w3.org/ns/json-ld#context" in the HTTP "Link" header. availability of such a JSON-LD context by using a link with the
relation type "http://www.w3.org/ns/json-ld#context" in the HTTP
"Link" header.
Using the latter approach to support discovery of a JSON-LD Context, Using the latter approach to support discovery of a JSON-LD Context,
the response to the GET request of Figure 3 against the URI of a set the response to the GET request of Figure 9 against the URI of a set
of links would be as shown in Figure 7. of links would be as shown in Figure 13.
HTTP/1.1 200 OK HTTP/1.1 200 OK
Date: Mon, 12 Aug 2019 10:48:22 GMT Date: Mon, 12 Aug 2019 10:48:22 GMT
Server: Apache-Coyote/1.1 Server: Apache-Coyote/1.1
Content-Type: application/linkset+json Content-Type: application/linkset+json
Link: <https://example.org/contexts/linkset.jsonld> Link: <https://example.org/contexts/linkset.jsonld>
; rel="http://www.w3.org/ns/json-ld#context" ; rel="http://www.w3.org/ns/json-ld#context"
; type="application/ld+json" ; type="application/ld+json"
Content-Length: 846 Content-Length: 1349
{ {
"linkset": [ "linkset": [
{ {
"anchor": "https://example.org/article/view/7507", "anchor": "https://example.org/resource1",
"author": [ "author": [
{ {
"href": "https://orcid.org/0000-0002-1825-0097" "href": "https://authors.example.net/johndoe",
"type": "application/rdf+xml"
} }
], ],
"item": [ "memento": [
{ {
"href": "https://example.org/article/7507/item/1", "href": "https://example.org/resource1?version=1",
"type": "application/pdf" "type": "text/html",
"datetime": "Thu, 13 Jun 2019 09:34:33 GMT"
}, },
{ {
"href": "https://example.org/article/7507/item/2", "href": "https://example.org/resource1?version=2",
"type": "text/csv" "type": "text/html",
"datetime": "Sun, 21 Jul 2019 12:22:04 GMT"
} }
], ],
"cite-as": [ "latest-version": [
{ {
"href": "https://doi.org/10.5555/12345680", "href": "https://example.org/resource1?version=3",
"title": "A Methodology for the Emulation of Architecture" "type": "text/html"
} }
] ]
}, },
{ {
"anchor": "https://example.com/links/article/7507", "anchor": "https://example.org/resource1?version=3",
"alternate": [ "predecessor-version": [
{ {
"href": "https://mirror.example.com/links/article/7507", "href": "https://example.org/resource1?version=2",
"type": "application/linkset" "type": "text/html"
}
]
},
{
"anchor": "https://example.org/resource1?version=2",
"predecessor-version": [
{
"href": "https://example.org/resource1?version=1",
"type": "text/html"
}
]
},
{
"anchor": "https://example.org/resource1#comment=1",
"author": [
{
"href": "https://authors.example.net/alice"
} }
] ]
} }
] ]
} }
Figure 7: Using a typed link to support discovery of a JSON-LD Figure 13: Using a typed link to support discovery of a JSON-LD
Context for a Set of Links Context for a Set of Links
In order to obtain the JSON-LD Context conveyed by the server, the In order to obtain the JSON-LD Context conveyed by the server, the
user agent issues an HTTP GET against the link target of the link user agent issues an HTTP GET against the link target of the link
with the "http://www.w3.org/ns/json-ld#context" relation type. The with the "http://www.w3.org/ns/json-ld#context" relation type. The
response to this GET is shown in Figure 8. This particular JSON-LD response to this GET is shown in Figure 14. This particular JSON-LD
context maps "application/linkset+json" representations of link sets context maps "application/linkset+json" representations of link sets
to Dublin Core Terms. It also renders each link relation as an to Dublin Core Terms. It also renders each link relation as a URI
absolute URI, inspired by the same approach used for Atom [RFC4287] Reference, inspired by the same approach used for Atom [RFC4287]
described in [RFC8288] appendix A.2 [2]. described in Appendix A.2 of [RFC8288].
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/ld+json Content-Type: application/ld+json
Content-Length: 638 Content-Length: 708
{ {
"@context": [ "@context": [
{ {
"@vocab": "http://www.iana.org/assignments/relation/", "@vocab": "http://www.iana.org/assignments/relation/",
"anchor": "@id", "anchor": "@id",
"href": "@id", "href": "@id",
"linkset": "@graph", "linkset": "@graph",
"_linkset": "@graph", "_linkset": "@graph",
"title": { "title": {
"@id": "http://purl.org/dc/terms/title" "@id": "http://purl.org/dc/terms/title"
}, },
"title*": { "title*": {
"@id": "http://purl.org/dc/terms/title" "@id": "http://purl.org/dc/terms/title"
}, },
"type": { "type": {
"@id": "http://purl.org/dc/terms/format" "@id": "http://purl.org/dc/terms/format"
},
"datetime": {
"@id": "http://purl.org/dc/terms/date"
} }
}, },
{ {
"language": "@language", "language": "@language",
"value": "@value", "value": "@value",
"hreflang": { "hreflang": {
"@id": "http://purl.org/dc/terms/language", "@id": "http://purl.org/dc/terms/language",
"@container": "@set" "@container": "@set"
} }
} }
] ]
} }
Figure 8: JSON-LD Context mapping to schema.org and IANA assignments Figure 14: JSON-LD Context mapping to Dublin Core Terms and IANA
assignments
Applying the JSON-LD context of Figure 8 to the link set of Figure 7 Applying the JSON-LD context of Figure 14 to the link set of
allows transforming the "application/linkset+json" link set to an RDF Figure 13 allows transforming the "application/linkset+json" link set
link set. Figure 9 shows the latter represented by means of the to an RDF link set. Figure 15 shows the latter represented by means
"text/turtle" RDF serialization. of the "text/turtle" RDF serialization.
<https://example.org/article/view/7507> <https://authors.example.net/johndoe>
<http://www.iana.org/assignments/relation/author> <http://purl.org/dc/terms/format>
<https://orcid.org/0000-0002-1825-0097> . "application/rdf+xml" .
<https://example.org/article/view/7507> <https://example.org/resource1#comment=1>
<http://www.iana.org/assignments/relation/item> <http://www.iana.org/assignments/relation/author>
<https://example.org/article/7507/item/1> . <https://authors.example.net/alice> .
<https://example.org/article/7507/item/1> <https://example.org/resource1>
<http://purl.org/dc/terms/format> <http://www.iana.org/assignments/relation/author>
"application/pdf" . <https://authors.example.net/johndoe> .
<https://example.org/article/view/7507> <https://example.org/resource1>
<http://www.iana.org/assignments/relation/item> <http://www.iana.org/assignments/relation/latest-version>
<https://example.org/article/7507/item/2> . <https://example.org/resource1?version=3> .
<https://example.org/article/7507/item/2> <https://example.org/resource1>
<http://purl.org/dc/terms/format> <http://www.iana.org/assignments/relation/memento>
"text/csv" . <https://example.org/resource1?version=1> .
<https://example.org/article/view/7507> <https://example.org/resource1>
<http://www.iana.org/assignments/relation/cite-as> <http://www.iana.org/assignments/relation/memento>
<https://doi.org/10.5555/12345680> . <https://example.org/resource1?version=2> .
<https://doi.org/10.5555/12345680> <https://example.org/resource1?version=1>
<http://purl.org/dc/terms/title> <http://purl.org/dc/terms/date>
"A Methodology for the Emulation of Architecture" . "Thu, 13 Jun 2019 09:34:33 GMT" .
<https://example.com/links/article/7507> <https://example.org/resource1?version=1>
<http://www.iana.org/assignments/relation/alternate> <http://purl.org/dc/terms/format>
<https://mirror.example.com/links/article/7507> . "text/html" .
<https://mirror.example.com/links/article/7507> <https://example.org/resource1?version=2>
<http://purl.org/dc/terms/format> <http://purl.org/dc/terms/date>
"application/linkset" . "Sun, 21 Jul 2019 12:22:04 GMT" .
<https://example.org/resource1?version=2>
<http://purl.org/dc/terms/format>
"text/html" .
<https://example.org/resource1?version=2>
<http://www.iana.org/assignments/relation/predecessor-version>
<https://example.org/resource1?version=1> .
<https://example.org/resource1?version=3>
<http://purl.org/dc/terms/format>
"text/html" .
<https://example.org/resource1?version=3>
<http://www.iana.org/assignments/relation/predecessor-version>
<https://example.org/resource1?version=2> .
Figure 9: RDF serialization of the link set resulting from applying Figure 15: RDF serialization of the link set resulting from
the JSON-LD context applying the JSON-LD context
Note that the JSON-LD context of Figure 8 does not handle (meta)link Note that the JSON-LD context of Figure 14 does not handle (meta)link
relations of type ""linkset"" as they are in conflict with the top- relations of type ""linkset"" as they are in conflict with the top-
level JSON key. A workaround is to rename the top-level key to level JSON key. A workaround is to rename the top-level key to
""_linkset"" in the "application/linkset+json" before transforming a ""_linkset"" in the "application/linkset+json" before transforming a
link set to JSON-LD. link set to JSON-LD.
Appendix B. Implementation Status
This section is to be removed before publishing as an RFC.
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.
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".
B.1. GS1
GS1 is a provider of barcodes (GS1 GTINs and EAN/UPC) for retail
products and manages an ecology of services and standards to leverage
them at a global scale. GS1 has indicated that it will implement
this "linkset" specification as a means to allow requesting and
representing links pertaining to products from various retailers.
Currently, the GS1 Digital Link specification makes an informative
reference to version 03 of the "linkset" I-D. GS1 expresses
confidence that this will become a normative reference in the next
iteration of that specification, likely to be ratified as a GS1
standard around February 2021.
B.2. FAIR Signposting Profile
The FAIR Signposting Profile is a community specification aimed at
improving machine navigation of scholarly objects on the web through
the use of typed web links pointing at e.g. web resources that are
part of a specific object, persistent identifiers for the object and
its authors, license information pertaining to the object. The
specification encourages the use of Linksets and initial
implementations are ongoing, for example, for the open source
Dataverse data repository platform that was initiated by Harvard
University and is meanwhile used by research institutions, worldwide.
B.3. 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).
Acknowledgements
Thanks for comments and suggestions provided by Phil Archer,
Dominique Guinard, Mark Nottingham, Julian Reschke, Stian Soiland-
Reyes, and Sarven Capadisli.
Authors' Addresses Authors' Addresses
Erik Wilde Erik Wilde
Axway Axway
Email: erik.wilde@dret.net Email: erik.wilde@dret.net
URI: http://dret.net/netdret/ URI: http://dret.net/netdret/
Herbert Van de Sompel Herbert Van de Sompel
Data Archiving and Networked Services Data Archiving and Networked Services
Email: herbert.van.de.sompel@dans.knaw.nl Email: herbert.van.de.sompel@dans.knaw.nl
URI: https://orcid.org/0000-0002-0715-6126 URI: https://orcid.org/0000-0002-0715-6126
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