[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-luff-json-hyper-schema) 00 01

Internet Engineering Task Force                           A. Wright, Ed.
Internet-Draft
Intended status: Informational                                   G. Luff
Expires: April 16, 2017                                 October 13, 2016


   JSON Hyper-Schema: A Vocabulary for Hypermedia Annotation of JSON
                draft-wright-json-schema-hyperschema-00

Abstract

   JSON Schema is a JSON based format for defining the structure of JSON
   data.  This document specifies hyperlink- and hypermedia-related
   keywords of JSON Schema for annotating JSON documents with hyperlinks
   and instructions for processing and manipulating remote JSON
   resources through hypermedia environments like HTTP.

Note to Readers

   The issues list for this draft can be found at <https://github.com/
   json-schema-org/json-schema-spec/issues>.

   For additional information, see <http://json-schema.org/>.

   To provide feedback, use this issue tracker, the communication
   methods listed on the homepage, or email the document editors.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 16, 2017.








Wright & Luff            Expires April 16, 2017                 [Page 1]


Internet-Draft              JSON Hyper-Schema               October 2016


Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Schema keywords . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  base  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  links . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  media . . . . . . . . . . . . . . . . . . . . . . . . . .   7
       4.3.1.  Properties of "media" . . . . . . . . . . . . . . . .   7
       4.3.2.  Example . . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  readOnly  . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Link Description Object . . . . . . . . . . . . . . . . . . .   8
     5.1.  href  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
       5.1.1.  URI Templating  . . . . . . . . . . . . . . . . . . .   9
     5.2.  rel . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  Security Considerations for "self" links  . . . . . .  13
     5.3.  title . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.4.  targetSchema  . . . . . . . . . . . . . . . . . . . . . .  15
       5.4.1.  Security Considerations for "targetSchema"  . . . . .  15
     5.5.  mediaType . . . . . . . . . . . . . . . . . . . . . . . .  16
       5.5.1.  Security concerns for "mediaType" . . . . . . . . . .  17
     5.6.  Submission Form Properties  . . . . . . . . . . . . . . .  18
       5.6.1.  method  . . . . . . . . . . . . . . . . . . . . . . .  18
       5.6.2.  encType . . . . . . . . . . . . . . . . . . . . . . .  18
       5.6.3.  schema  . . . . . . . . . . . . . . . . . . . . . . .  19
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  20
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  21
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22




Wright & Luff            Expires April 16, 2017                 [Page 2]


Internet-Draft              JSON Hyper-Schema               October 2016


1.  Introduction

   JSON Schema is a JSON based format for defining the structure of JSON
   data.  This document specifies hyperlink- and hypermedia-related
   keywords of JSON Schema.

   The term JSON Hyper-Schema is used to refer to a JSON Schema that
   uses these keywords.

   This specification will use the terminology defined by the JSON
   Schema core specification [json-schema].  It is advised that readers
   have a copy of this specification.

2.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The terms "schema", "instance", "property" and "item" are to be
   interpreted as defined in the JSON Schema core specification
   [json-schema].

3.  Overview

   This document describes how JSON Schema can be used to define
   hyperlinks on instance data.  It also defines how to provide
   additional information required to interpret JSON data as rich
   multimedia documents.

   As with all JSON Schema keywords, all the keywords described in the
   "Schema Keywords" section are optional.  The minimal valid JSON
   Hyper-schema is the blank object.

   Here is an example JSON Schema defining hyperlinks, and providing a
   multimedia interpretation for the "imgData" property:















Wright & Luff            Expires April 16, 2017                 [Page 3]


Internet-Draft              JSON Hyper-Schema               October 2016


   {
       "title": "Written Article",
       "type": "object",
       "properties": {
           "id": {
               "title": "Article Identifier",
               "type": "number",
               "readOnly": true
           },
           "title": {
               "title": "Article Title",
               "type": "string"
           },
           "authorId": {
               "type": "integer"
           },
           "imgDataPng": {
               "title": "Article Illustration (thumbnail)",
               "type": "string",
               "media": {
                   "binaryEncoding": "base64",
                   "type": "image/png"
               }
           }
       },
       "required" : ["id", "title", "authorId"],
       "links": [
           {
               "rel": "self",
               "href": "/article{?id}"
           },
           {
               "rel": "author",
               "href": "/user?id={authorId}"
           }
       ]
   }


   This example schema defines the properties of the instance.  For the
   "imgData" property, it specifies that that it should be
   base64-decoded and the resulting binary data treated as a PNG image.
   It also defines link relations for the instance, with URIs
   incorporating values from the instance.  [[CREF1: "id" probably
   should not normally be a required keyword, since new instances will
   have an unknown "id" property until is it assigned by the server.
   However, this property is used in a link, and without it, multiple
   different instances would be given the same rel=self URI!]]



Wright & Luff            Expires April 16, 2017                 [Page 4]


Internet-Draft              JSON Hyper-Schema               October 2016


   An example of a JSON instance described by the above schema might be:


   {
       "id": 15,
       "title": "Example data",
       "authorId": 105,
       "imgData": "iVBORw...kJggg=="
   }


   The base-64 data has been abbreviated for readability.

4.  Schema keywords

4.1.  base

   If present, this keyword is resolved against the current URI base
   that the entire instance is found within, and sets the new URI base
   for URI references within the instance.  It is therefore the first
   URI Reference resolved, regardless of which order it was found in.

   The URI is computed from the provided URI template using the same
   process described for the "href" (Section 5.1) property of a Link
   Description Object.

   An example of a JSON schema using "base":


   {
       "base": "/object/{id}",
       "links": [
           {
               "rel": "self",
               "href": ""
           },
           {
               "rel": "next",
               "href": "{next_id}"
           }
       ]
   }









Wright & Luff            Expires April 16, 2017                 [Page 5]


Internet-Draft              JSON Hyper-Schema               October 2016


   An example of a JSON instance using this schema to produce rel="self"
   and rel="next" links:


   {
       "id": "41",
       "next_id": "42"
   }


   If the document URI is <http://example.com/?id=41>, then the new URI
   base becomes <http://example.com/object/41>

   Resolving the two Link Description Objects against this URI base
   creates two links exactly equivelant to these absolute-form HTTP Link
   headers:

   o  Link: <http://example.com/object/41>;rel=self

   o  Link: <http://example.com/object/42>;rel=next

4.2.  links

   The "links" property of schemas is used to associate Link Description
   Objects with instances.  The value of this property MUST be an array,
   and the items in the array must be Link Description Objects, as
   defined below.

   An example schema using the "links" keyword could be:

   {
       "title": "Schema defining links",
       "links": [
           {
               "rel": "self",
               "href": "{id}"
           },
           {
               "rel": "parent",
               "href": "{parent}"
           }
       ]
   }








Wright & Luff            Expires April 16, 2017                 [Page 6]


Internet-Draft              JSON Hyper-Schema               October 2016


4.3.  media

   The "media" property indicates that this instance contains non-JSON
   data encoded in a JSON string.  It describes the type of content and
   how it is encoded.

   The value of this property MUST be an object.  The value of this
   property SHOULD be ignored if the instance described is not a string.

4.3.1.  Properties of "media"

   The value of the "media" keyword MAY contain any of the following
   properties:

4.3.1.1.  binaryEncoding

   If the instance value is a string, this property defines that the
   string SHOULD be interpreted as binary data and decoded using the
   encoding named by this property.  RFC 2045, Sec 6.1 [RFC2045] lists
   the possible values for this property.

4.3.1.2.  type

   The value of this property must be a media type, as defined by RFC
   2046 [RFC2046].  This property defines the media type of instances
   which this schema defines.

   If the "binaryEncoding" property is not set, but the instance value
   is a string, then the value of this property SHOULD specify a text
   document type, and the character set SHOULD be the character set into
   which the JSON string value was decoded (for which the default is
   Unicode).

4.3.2.  Example

















Wright & Luff            Expires April 16, 2017                 [Page 7]


Internet-Draft              JSON Hyper-Schema               October 2016


   Here is an example schema, illustrating the use of "media":


   {
       "type": "string",
       "media": {
           "binaryEncoding": "base64",
           "type": "image/png"
       }
   }


   Instances described by this schema should be strings, and their
   values should be interpretable as base64-encoded PNG images.

   Another example:


   {
       "type": "string",
       "media": {
           "mediaType": "text/html"
       }
   }


   Instances described by this schema should be strings containing HTML,
   using whatever character set the JSON string was decoded into
   (default is Unicode).

4.4.  readOnly

   If it has a value of boolean true, this keyword indicates that the
   value of the instance is managed exclusively by the server or the
   owning authority, and attempts by a user agent to modify the value of
   this property are expected to be ignored or rejected by a server.

   For example, this property would be used to mark a server-generated
   serial number as read-only.

   The value of this keyword MUST be a boolean.  The default value is
   false.

5.  Link Description Object

   A Link Description Object (LDO) is used to describe a single link
   relation from the instance to another resource.  A Link Description
   Object must be an object.



Wright & Luff            Expires April 16, 2017                 [Page 8]


Internet-Draft              JSON Hyper-Schema               October 2016


   The link description format can be used without JSON Schema, and use
   of this format can be declared by referencing the normative link
   description schema as the schema for the data structure that uses the
   links.  The URI of the normative link description schema is:
   http://json-schema.org/draft-04/links (draft-04 version).

   "Form"-like functionality can be defined by use of the "method" and
   "schema" keywords, which supplies a schema describing the data to
   supply to the server.

5.1.  href

   The value of the "href" link description property is a template used
   to determine the target URI of the related resource.  The value of
   the instance property MUST be resolved as a URI-reference [RFC3986]
   against the base URI of the instance.

   This property is REQUIRED.

5.1.1.  URI Templating

   The value of "href" is to be used as a URI Template, as defined in
   RFC 6570 [RFC6570].  However, some special considerations apply:

5.1.1.1.  Pre-processing

   [[CREF2: This pre-processing section is subject to significant change
   in upcoming drafts.]]

   The URI Template specification [RFC6570] restricts the set of
   characters available for variable names.  Property names in JSON,
   however, can be any UTF-8 string.

   To allow the use of any JSON property name in the template, before
   using the value of "href" as a URI Template, the following pre-
   processing rules MUST be applied, in order:

5.1.1.1.1.  Bracket escaping

   The purpose of this step is to allow the use of brackets to percent-
   encode variable names inside curly brackets.  Variable names to be
   escaped are enclosed within rounded brackets, with the close-rounded-
   bracket character ")" being escaped as a pair of close-rounded-
   brackets "))".  Since the empty string is not a valid variable name
   in RFC 6570, an empty pair of brackets is replaced with "%65mpty".

   The rules are as follows:




Wright & Luff            Expires April 16, 2017                 [Page 9]


Internet-Draft              JSON Hyper-Schema               October 2016


   Find the largest possible sections of the text such that:

      do not contain an odd number of close-rounded-bracket characters
      ")" in sequence in that section of the text

      are surrounded by a pair of rounded brackets: ( ), where

      the surrounding rounded brackets are themselves contained within a
      pair of curly brackets: { }

   Each of these sections of the text (including the surrounding rounded
   brackets) MUST be replaced, according to the following rules:

      If the brackets contained no text (the empty string), then they
      are replaced with "%65mpty" (which is "empty" with a percent-
      encoded "e")

      Otherwise, the enclosing brackets are removed, and the inner text
      used after the following modifications

         all pairs of close-brackets "))" are replaced with a single
         close bracket

         after that, the text is replaced with its percent-encoded
         equivalent, such that the result is a valid RFC 6570 variable
         name (note that this requires encoding characters such as "*"
         and "!")

5.1.1.1.2.  Replacing $

   After the above substitutions, if the character "$" (dollar sign)
   appears within a pair of curly brackets, then it MUST be replaced
   with the text "%73elf" (which is "self" with a percent-encoded "s").

   The purpose of this stage is to allow the use of the instance value
   itself (instead of its object properties or array items) in the URI
   Template, by the special value "%73elf".

5.1.1.1.3.  Choice of special-case values

   The special-case values of "%73elf" and "%65mpty" were chosen because
   they are unlikely to be accidentally generated by either a human or
   automated escaping.








Wright & Luff            Expires April 16, 2017                [Page 10]


Internet-Draft              JSON Hyper-Schema               October 2016


5.1.1.1.4.  Examples

    For example, here are some possible values for "href", followed by
                     the results after pre-processing:

             +-----------------------+-----------------------+
             | Input                 | Output                |
             +-----------------------+-----------------------+
             | "no change"           | "no change"           |
             | "(no change)"         | "(no change)"         |
             | "{(escape space)}"    | "{escape%20space}"    |
             | "{(escape+plus)}"     | "{escape%2Bplus}"     |
             | "{(escape*asterisk)}" | "{escape%2Aasterisk}" |
             | "{(escape(bracket)}"  | "{escape%28bracket}"  |
             | "{(escape))bracket)}" | "{escape%29bracket}"  |
             | "{(a))b)}"            | "{a%29b}              |
             | "{(a (b)))}"          | "{a%20%28b%29}        |
             | "{()}"                | "{%65mpty}            |
             | "{+$*}"               | "{+%73elf*}           |
             | "{+($)*}"             | "{+%24*}              |
             +-----------------------+-----------------------+

      Note that in the final example, because the "+" was outside the
    brackets, it remained unescaped, whereas in the fourth example the
                             "+" was escaped.

5.1.1.2.  Values for substitution

   After pre-processing, the URI Template is filled out using data from
   the instance.  To allow the use of any object property (including the
   empty string), array index, or the instance value itself, the
   following rules are defined:

   For a given variable name in the URI Template, the value to use is
   determined as follows:

      If the variable name is "%73elf", then the instance value itself
      MUST be used.

      If the variable name is "%65mpty", then the instances's empty-
      string ("") property MUST be used (if it exists).

      If the instance is an array, and the variable name is a
      representation of a non-negative integer, then the value at the
      corresponding array index MUST be used (if it exists).

      Otherwise, the variable name should be percent-decoded, and the
      corresponding object property MUST be used (if it exists).



Wright & Luff            Expires April 16, 2017                [Page 11]


Internet-Draft              JSON Hyper-Schema               October 2016


5.1.1.2.1.  Converting to strings

   When any value referenced by the URI template is null, a boolean or a
   number, then it should first be converted into a string as follows:

      null values SHOULD be replaced by the text "null"

      boolean values SHOULD be replaced by their lower-case equivalents:
      "true" or "false"

      numbers SHOULD be replaced with their original JSON
      representation.

   In some software environments the original JSON representation of a
   number will not be available (there is no way to tell the difference
   between 1.0 and 1), so any reasonable representation should be used.
   Schema and API authors should bear this in mind, and use other types
   (such as string or boolean) if the exact representation is important.

5.1.1.3.  Missing values

   Sometimes, the appropriate values will not be available.  For
   example, the template might specify the use of object properties, but
   the instance is an array or a string.

   If any of the values required for the template are not present in the
   JSON instance, then substitute values MAY be provided from another
   source (such as default values).  Otherwise, the link definition
   SHOULD be considered not to apply to the instance.

5.2.  rel

   The value of the "rel" property indicates the name of the relation to
   the target resource.  The value MUST be a registered link relation
   from the IANA Link Relation Type Registry established in RFC 5988
   [RFC5988], or a normalized URI following the URI production of RFC
   3986 [RFC3986].

   The relation to the target is interpreted as from the instance that
   the schema (or sub-schema) applies to, not any larger document that
   the instance may have been found in.

   Relationship definitions are not normally media type dependent, and
   users are encouraged to utilize existing accepted relation
   definitions.






Wright & Luff            Expires April 16, 2017                [Page 12]


Internet-Draft              JSON Hyper-Schema               October 2016


   For example, if a schema is defined:

   {
       "links": [{
           "rel": "self",
           "href": "{id}"
       }, {
           "rel": "up",
           "href": "{upId}"
       }]
   }

   And if a collection of instance resources were retrieved with JSON
   representation:

   GET /Resource/

   [{
       "id": "thing",
       "upId": "parent"
   }, {
       "id": "thing2",
       "upId": "parent"
   }]

   This would indicate that for the first item in the collection, its
   own (self) URI would resolve to "/Resource/thing" and the first
   item's "up" relation SHOULD be resolved to the resource at
   "/Resource/parent".

   Note that these relationship values are case-insensitive, consistent
   with their use in HTML and the HTTP Link header [RFC5988].

5.2.1.  Security Considerations for "self" links

   When link relation of "self" is used to denote a full representation
   of an object, the user agent SHOULD NOT consider the representation
   to be the authoritative representation of the resource denoted by the
   target URI if the target URI is not equivalent to or a sub-path of
   the the URI used to request the resource representation which
   contains the target URI with the "self" link.










Wright & Luff            Expires April 16, 2017                [Page 13]


Internet-Draft              JSON Hyper-Schema               October 2016


   For example, if a hyper schema was defined:

   {
       "links": [{
           "rel": "self",
           "href": "{id}"
       }]
   }

   And a resource was requested from somesite.com:


   GET /foo/


   With a response of (with newlines and whitespace added):

   Content-Type: application/json; profile="http://example.com/alpha"

   [{
       "id": "bar",
       "name": "This representation can be safely treated
                as authoritative "
   }, {
       "id": "/baz",
       "name": "This representation should not be treated as
                authoritative the user agent should make request the
                resource from '/baz' to ensure it has the authoritative
                representation"
   }, {
       "id": "http://othersite.com/something",
       "name": "This representation
                should also not be treated as authoritative and the
                target resource representation should be retrieved
                for the authoritative representation"
   }]

5.3.  title

   This property defines a title for the link.  The value must be a
   string.

   User agents MAY use this title when presenting the link to the user.








Wright & Luff            Expires April 16, 2017                [Page 14]


Internet-Draft              JSON Hyper-Schema               October 2016


5.4.  targetSchema

   This property provides a schema that is expected to describe the link
   target, including what a client can expect if it makes an HTTP GET
   request, and what it should send if it replaces the resource in an
   HTTP PUT request.  This property is advisory only.

5.4.1.  Security Considerations for "targetSchema"

   This property has similar security concerns to that of "mediaType".
   Clients MUST NOT use the value of this property to aid in the
   interpretation of the data received in response to following the
   link, as this leaves "safe" data open to re-interpretation.

   For example, suppose two programmers are having a discussion about
   web security using a text-only message board.  Here is some data from
   that conversation, with a URI of:
   http://forum.example.com/topics/152/comments/13

   {
       "topicId": 152,
       "commentId": 13,
       "from": {
           "name": "Jane",
           "id": 5
       },
       "to": {
           "name": "Jason",
           "id": 8
       },
       "message": "It's easy, just add some HTML like
            this: <script>doSomethingEvil()</script>"
   }

   The message string was split over two lines for readability.

   A third party might then write provide the following Link Description
   Object at another location:













Wright & Luff            Expires April 16, 2017                [Page 15]


Internet-Draft              JSON Hyper-Schema               October 2016


   {
       "rel": "evil-attack",
       "href": "http://forum.example.com/topics/152/comments/13",
       "targetSchema": {
           "properties": {
               "message": {
                   "description": "Re-interpret `message` as HTML",
                   "media": {
                       "type": "text/html"
                   }
               }
           }
       }
   }

   If the client used this "targetSchema" value when interpreting the
   above data, then it might display the contents of "message" as HTML.
   At this point, the JavaScript embedded in the message might be
   executed (in the context of the "forum.example.com" domain).

5.5.  mediaType

   The value of this property is advisory only, and represents the media
   type RFC 2046 [RFC2046], that is expected to be returned when
   fetching this resource.  This property value MAY be a media range
   instead, using the same pattern defined in RFC 7231, section 5.3.1 -
   HTTP "Accept" header [RFC7231].

   This property is analogous to the "type" property of <a> elements in
   HTML (advisory content type), or the "type" parameter in the HTTP
   Link header [RFC5988].  User agents MAY use this information to
   inform the interface they present to the user before the link is
   followed, but this information MUST NOT use this information in the
   interpretation of the resulting data.  When deciding how to interpret
   data obtained through following this link, the behaviour of user
   agents MUST be identical regardless of the value of the this
   property.

   If this property's value is specified, and the link's target is to be
   obtained using any protocol that supports the HTTP/1.1 "Accept"
   header RFC 7231, section 5.3.1 [RFC7231], then user agents MAY use
   the value of this property to aid in the assembly of that header when
   making the request to the server.

   If this property's value is not specified, then the value should be
   taken to be "application/json".





Wright & Luff            Expires April 16, 2017                [Page 16]


Internet-Draft              JSON Hyper-Schema               October 2016


   For example, if a schema is defined:


   {
       "links": [{
           "rel": "self",
           "href": "/{id}/json"
       }, {
           "rel": "alternate",
           "href": "/{id}/html",
           "mediaType": "text/html"
       }, {
           "rel": "alternate",
           "href": "/{id}/rss",
           "mediaType": "application/rss+xml"
       }, {
           "rel": "icon",
           "href": "{id}/icon",
           "mediaType": "image/*"
       }]
   }


   A suitable instance described by this schema would have four links
   defined.  The link with a "rel" value of "self" would have an
   expected MIME type of "application/json" (the default).  The two
   links with a "rel" value of "alternate" specify the locations of HTML
   and RSS versions of the current item.  The link with a "rel" value of
   "icon" links to an image, but does not specify the exact format.

   A visual user agent displaying the item from the above example might
   present a button representing an RSS feed, which when pressed passes
   the target URI (calculated "href" value) to an view more suited to
   displaying it, such as a news feed aggregator tab.

   Note that presenting the link in the above manner, or passing the URI
   to a news feed aggregator view does not constitute interpretation of
   the data, but an interpretation of the link.  The interpretation of
   the data itself is performed by the news feed aggregator, which
   SHOULD reject any data that would not have also been interpreted as a
   news feed, had it been displayed in the main view.

5.5.1.  Security concerns for "mediaType"

   The "mediaType" property in link definitions defines the expected
   format of the link's target.  However, this is advisory only, and
   MUST NOT be considered authoritative.




Wright & Luff            Expires April 16, 2017                [Page 17]


Internet-Draft              JSON Hyper-Schema               October 2016


   When choosing how to interpret data, the type information provided by
   the server (or inferred from the filename, or any other usual method)
   MUST be the only consideration, and the "mediaType" property of the
   link MUST NOT be used.  User agents MAY use this information to
   determine how they represent the link or where to display it (for
   example hover-text, opening in a new tab).  If user agents decide to
   pass the link to an external program, they SHOULD first verify that
   the data is of a type that would normally be passed to that external
   program.

   This is to guard against re-interpretation of "safe" data, similar to
   the precautions for "targetSchema".

5.6.  Submission Form Properties

   The following properties also apply to Link Description Objects, and
   provide functionality analogous to HTMLforms [W3C.CR-html5-20140731],
   by providing a means for making a request with client- or user-
   selected information.

5.6.1.  method

   This property specifies that the client can construct a templated
   query or non-idempotent request to a resource.

   If "method" is "get", the link identifies how a user can compute the
   URI of an arbritrary resource.  For example, how compute a link to a
   page of search results relating to the instance, for a user-selected
   query term.  Despite being named after GET, there is no constraint on
   the method or protocol used to interact with the remote resource.

   If "method" is "post", the link specifies how a user can construct a
   document to submit to the link target for evaluation.

   Values for this property SHOULD be lowercase, and SHOULD be compared
   case-insensitive.  Use of other values not defined here SHOULD be
   ignored.

5.6.2.  encType

   If present, this property indicates the media type format the client
   should use to encode a query parameter or send to the server. posting
   to the collection of instances at the target resource.  If the method
   is "get", this will indicate how to encode the query-string that is
   appended to the "href" link target.  If the method is "post", this
   indicates which media type to send to the server and how to encode
   it.




Wright & Luff            Expires April 16, 2017                [Page 18]


Internet-Draft              JSON Hyper-Schema               October 2016


   For example, with the following schema:

   {
       "links": [{
           "encType": "application/x-www-form-urlencoded",
           "method": "get",
           "href": "/Product/",
           "properties": {
               "name": {
                   "description": "name of the product"
               }
           }
       }]
   }

   This indicates that the client can query the server for instances
   that have a specific name.

   For example:


   /Product/?name=Slinky


   If the method is "post", "application/json" is the default media
   type.

5.6.3.  schema

   This property contains a schema which defines the acceptable
   structure of the document being encoded according to the "encType"
   property.

   Note that this does not provide data for any URI templates.  This is
   a separate concept from the "targetSchema" property, which is
   describing the target information resource (including for replacing
   the contents of the resource in a PUT request), unlike "schema" which
   describes the user-submitted request data to be evaluated by the
   resource.

6.  References

6.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
              <http://www.rfc-editor.org/info/rfc2045>.



Wright & Luff            Expires April 16, 2017                [Page 19]


Internet-Draft              JSON Hyper-Schema               October 2016


   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/
              RFC6570, March 2012,
              <http://www.rfc-editor.org/info/rfc6570>.

   [json-schema]
              Wright, A., "JSON Schema: A Media Type for Describing JSON
              Documents", draft-wright-json-schema-00 (work in
              progress), October 2016.

6.2.  Informative References

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046, DOI
              10.17487/RFC2046, November 1996,
              <http://www.rfc-editor.org/info/rfc2046>.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988, DOI 10.17487/
              RFC5988, October 2010,
              <http://www.rfc-editor.org/info/rfc5988>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI
              10.17487/RFC7231, June 2014,
              <http://www.rfc-editor.org/info/rfc7231>.

   [W3C.CR-html5-20140731]
              Berjon, R., Faulkner, S., Leithead, T., Navara, E.,
              O&#039;Connor, E., and S. Pfeiffer, "HTML5", World Wide
              Web Consortium CR CR-html5-20140731, July 2014,
              <http://www.w3.org/TR/2014/CR-html5-20140731>.










Wright & Luff            Expires April 16, 2017                [Page 20]


Internet-Draft              JSON Hyper-Schema               October 2016


Appendix A.  Acknowledgments

   Thanks to Gary Court, Francis Galiegue, Kris Zyp, and Geraint Luff
   for their work on the initial drafts of JSON Schema.

   Thanks to Jason Desrosiers, Daniel Perrett, Erik Wilde, Ben Hutton,
   Evgeny Poberezkin, and Henry H.  Andrews for their submissions and
   patches to the document.

Appendix B.  Change Log

   [[CREF3: This section to be removed before leaving Internet-Draft
   status.]]

   draft-wright-json-schema-hyperschema-00

      *  "rel" is now optional

      *  rel="self" no longer changes URI base

      *  Added "base" keyword to change instance URI base

      *  Removed "root" link relation

      *  Removed "create" link relation

      *  Removed "full" link relation

      *  Removed "instances" link relation

      *  Removed special behavior for "describedBy" link relation

      *  Removed "pathStart" keyword

      *  Removed "fragmentResolution" keyword

      *  Updated references to JSON Pointer, HTML

      *  Changed behavior of "method" property to align with hypermedia
         best current practices

   draft-luff-json-hyper-schema-01

      *  Split from main specification.







Wright & Luff            Expires April 16, 2017                [Page 21]


Internet-Draft              JSON Hyper-Schema               October 2016


Authors' Addresses

   Austin Wright (editor)

   EMail: aaa@bzfx.net


   Geraint Luff
   Cambridge
   UK

   EMail: luffgd@gmail.com







































Wright & Luff            Expires April 16, 2017                [Page 22]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/