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Internet Engineering Task Force                              K. Zyp, Ed.
Internet-Draft                                             SitePen (USA)
Intended status: Informational                            March 23, 2010
Expires: September 24, 2010


   A JSON Media Type for Describing the Structure and Meaning of JSON
                               Documents
                        draft-zyp-json-schema-02

Abstract

   JSON (JavaScript Object Notation) Schema defines the media type
   application/schema+json, a JSON based format for defining the
   structure of JSON data.  JSON Schema provides a contract for what
   JSON data is required for a given application and how to interact
   with it.  JSON Schema is intended to define validation,
   documentation, hyperlink navigation, and interaction control of JSON
   data.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 24, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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 BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Design Considerations  . . . . . . . . . . . . . . . . . .  6
   4.  Schema/Instance Association  . . . . . . . . . . . . . . . . .  6
     4.1.  Self-Descriptive Schema  . . . . . . . . . . . . . . . . .  7
   5.  Core Schema Definition . . . . . . . . . . . . . . . . . . . .  7
     5.1.  type . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  properties . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.3.  items  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.4.  optional . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.5.  additionalProperties . . . . . . . . . . . . . . . . . . .  9
     5.6.  requires . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.7.  minimum  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.8.  maximum  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.9.  minimumCanEqual  . . . . . . . . . . . . . . . . . . . . . 10
     5.10. maximumCanEqual  . . . . . . . . . . . . . . . . . . . . . 10
     5.11. minItems . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.12. maxItems . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.13. uniqueItems  . . . . . . . . . . . . . . . . . . . . . . . 10
     5.14. pattern  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.15. maxLength  . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.16. minLength  . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.17. enum . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.18. title  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.19. description  . . . . . . . . . . . . . . . . . . . . . . . 11
     5.20. format . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.21. contentEncoding  . . . . . . . . . . . . . . . . . . . . . 12
     5.22. default  . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.23. divisibleBy  . . . . . . . . . . . . . . . . . . . . . . . 13
     5.24. disallow . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.25. extends  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  Hyper Schema . . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  links  . . . . . . . . . . . . . . . . . . . . . . . . . . 13
       6.1.1.  Link Description Object  . . . . . . . . . . . . . . . 14



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     6.2.  fragmentResolution . . . . . . . . . . . . . . . . . . . . 18
       6.2.1.  dot-delimited fragment resolution  . . . . . . . . . . 18
       6.2.2.  slash-delimited fragment resolution  . . . . . . . . . 19
     6.3.  root . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     6.4.  readonly . . . . . . . . . . . . . . . . . . . . . . . . . 19
     6.5.  pathStart  . . . . . . . . . . . . . . . . . . . . . . . . 20
     6.6.  mediaType  . . . . . . . . . . . . . . . . . . . . . . . . 20
     6.7.  alternate  . . . . . . . . . . . . . . . . . . . . . . . . 20
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
     8.1.  Registry of Link Relations . . . . . . . . . . . . . . . . 21
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 22
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 23
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 24



































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1.  Introduction

   JSON (JavaScript Object Notation) Schema is a JSON media type for
   defining the structure of JSON data.  JSON Schema provides a contract
   for what JSON data is required for a given application and how to
   interact with it.  JSON Schema is intended to define validation,
   documentation, hyperlink navigation, and interaction control of JSON
   data.

2.  Conventions

   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.

3.  Overview

   JSON Schema defines the media type application/schema+json for
   describing the structure of other JSON documents.  JSON Schema is
   JSON-based and includes facilities for describing the structure of
   JSON documents in terms of allowable values, descriptions, and
   interpreting relations with other resources.

   JSON Schema format is organized into several separate definitions.
   The first definition is the core schema specification.  This
   definition is primary concerned with describing a JSON structure and
   specifying valid elements in the structure.  The second definition is
   the Hyper Schema specification which is intended define elements in a
   structure that can be interpreted as hyperlinks.  Hyper Schema builds
   on JSON Schema to describe the hyperlink structure of other JSON
   documents.  This allows user agents to be able to successfully
   navigate JSON documents based on their schemas.

   Cumulatively JSON Schema acts as a meta-document that can be used to
   define the required type and constraints on property values, as well
   as define the meaning of the property values for the purpose of
   describing a resource and determining hyperlinks within the
   representation.

   An example JSON Schema that describes products might look like:











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   {
     "name":"Product",
     "properties":{
       "id":{
         "type":"number",
         "description":"Product identifier"
       },
       "name":{
         "description":"Name of the product",
         "type":"string"
       },
       "price":{
         "type": "number",
         "minimum":0
       },
       "tags":{
         "optional":true,
         "type":"array",
         "items":{
            "type":"string"
         }
       }
     },
     "links":[
       {
         "rel":"full",
         "href":"{id}"
       },
       {
         "rel":"comments",
         "href":"comments/?id={id}"
       }
     ]
   }

   This schema defines the properties of the instance JSON documents and
   their required properties (id, name, and price) as well as an
   optional property (tags).  This also defines the link relations of
   the instance JSON documents.

3.1.  Terminology

   For this specification, a schema will be used to denote a JSON Schema
   definition, and an instance refers to the JSON object or array that
   the schema will be describing and validating






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3.2.  Design Considerations

   The JSON Schema media type does not attempt to dictate the structure
   of JSON representations that contain data, but rather provides a
   separate format for flexibly communicating how a JSON representation
   should be interpreted and validated, such that user agents can
   properly understand acceptable structures and extrapolate hyperlink
   information with the JSON document.  It is acknowledged that JSON
   documents come in a variety of structures, and JSON is unique in that
   the structure of stored data structures often prescribes a non-
   ambiguous definite JSON representation.  Attempting to force a
   specific structure is generally not viable, and therefore JSON Schema
   allows for great flexibility in the structure of JSON data that it
   describes.

   This specification is protocol agnostic.  The underlying protocol
   (such as HTTP) should sufficiently define the semantics of the
   client-server interface, the retrieval of resource representations
   linked to by JSON representations, and modification of those
   resources.  The goal of this format is to sufficiently describe JSON
   structures such that one can utilize existing information available
   in existing JSON representations from a large variety of services
   that leverage a representational state transfer architecture using
   existing protocols.

4.  Schema/Instance Association

   JSON Schema instances are correlated to their schema by the
   "describedby" relation, where the schema is defined to be the target
   of the relation.  Instance representations may be of the application/
   json media type or any other subtype.  Consequently, dictating how an
   instance representation should specify the relation to the schema is
   beyond the normative scope of this document (since this document
   specifically defines the JSON Schema media type, and no other), but
   it is recommended that instances specify their schema so that user
   agents can interpret the instance representation and messages may
   retain the self-descriptive characteristic, avoiding the need for
   out-of-band information about instance data.  Two approaches are
   recommended for declaring the relation to the schema that describes
   the meaning of a JSON instance's (or collection of instances)
   structure.  A MIME type parameter named "profile" or a Link header
   with a relation of "describedby" SHOULD be used:


   Content-Type: application/json;
                 profile=http://json.com/my-hyper-schema

   or if the content is being transferred by a protocol (such as HTTP)



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   that provides headers, a Link header can be used:


   Link: <http://json.com/my-hyper-schema>; rel="describedby"

   Instances MAY specify multiple schemas, to indicate all the schemas
   that are applicable to the data.  The instance data may have multiple
   schemas that it is defined by (the instance data should be valid for
   those schemas).  Or if the document is a collection of instances, the
   collection may contain instances from different schemas.  When
   collections contain heterogeneous instances, the pathStart attribute
   MAY be specified in the schema to disambiguate which schema should be
   applied for each item in the collection.

4.1.  Self-Descriptive Schema

   JSON Schemas are themselves instances for the schema schemas.  A
   self-describing JSON Schema for the core JSON Schema can be found at
   http://json-schema.org/schema and the hyper schema self-description
   can be found at: http://json-schema.org/hyper-schema.  All schemas
   used within a protocol with media type definitions SHOULD include a
   MIME parameter that refers to the self-descriptive hyper schema or
   another schema that extends this hyper schema:


   Content-Type: application/json;
                 profile=http://www.json-schema.org/hyper-schema

5.  Core Schema Definition

   A JSON Schema is a JSON Object that defines various attributes of the
   instance and defines it's usage and valid values.  A JSON Schema is a
   JSON Object with schema attribute properties.  The following is the
   grammar of a JSON Schema:

   And an example JSON Schema definition could look like:


   {"description":"A person",
    "type":"object",

    "properties":
     {"name": {"type":"string"},
      "age" : {"type":"integer",
        "maximum":125}}
   }

   A JSON Schema object may have any of the following properties, called



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   schema attributes (all attributes are optional):

5.1.  type

      Union type definition - An array with two or more items which
      indicates a union of type definitions.  Each item in the array may
      be a simple type definition or a schema.  The instance value is
      valid if it is of the same type as one the type definitions in the
      array or if it is valid by one of the schemas in the array.  For
      example to indicate that a string or number is a valid: {"type":
      ["string","number"]}

      Simple type definition - A string indicating a primitive or simple
      type.  The following are acceptable strings:

         string - Value must be a string.

         number - Value must be a number, floating point numbers are
         allowed.

         integer - Value must be an integer, no floating point numbers
         are allowed.  This is a subset of the number type.

         boolean - Value must be a boolean.

         object - Value must be an object.

         array - Value must be an array.

         null - Value must be null.  Note this is mainly for purpose of
         being able use union types to define nullability.

         any - Value may be of any type including null.  If the property
         is not defined or is not in this list, than any type of value
         is acceptable.  Other type values may be used for custom
         purposes, but minimal validators of the specification
         implementation can allow any instance value on unknown type
         values.

5.2.  properties

   This should be an object type definition, which is an object with
   property definitions that correspond to instance object properties.
   When the instance value is an object, the property values of the
   instance object must conform to the property definitions in this
   object.  In this object, each property definition's value should be a
   schema, and the property's name should be the name of the instance
   property that it defines.



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5.3.  items

   This should be a schema or an array of schemas.  When this is an
   object/schema and the instance value is an array, all the items in
   the array must conform to this schema.  When this is an array of
   schemas and the instance value is an array, each position in the
   instance array must conform to the schema in the corresponding
   position for this array.  This called tuple typing.  When tuple
   typing is used, additional items are allowed, disallowed, or
   constrained by the additionalProperties attribute using the same
   rules as extra properties for objects.  The default value is an empty
   schema which allows any value for items in the instance array.

5.4.  optional

   This indicates that the instance property in the instance object is
   optional.  This is false by default.

5.5.  additionalProperties

   This provides a default property definition for all properties that
   are not explicitly defined in an object type definition.  The value
   must be a schema.  If false is provided, no additional properties are
   allowed, and the schema can not be extended.  The default value is an
   empty schema which allows any value for additional properties.

5.6.  requires

   This indicates that if this property is present in the containing
   instance object, the property given by requires attribute must also
   be present in the containing instance object.  The value of this
   property may be a string, indicating the require property name.  Or
   the value may be a schema, in which case the containing instance must
   be valid by the schema if the property is present.  For example if a
   object type definition is defined:


   {
     "state":
     {
       "optional":true
     },
     "town":
     {
       "requires":"state",
       "optional":true
     }
   }



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   An instance must include a state property if a town property is
   included.  If a town property is not included, the state property is
   optional.

5.7.  minimum

   This indicates the minimum value for the instance property when the
   type of the instance value is a number.

5.8.  maximum

   This indicates the minimum value for the instance property when the
   type of the instance value is a number.

5.9.  minimumCanEqual

   If the minimum is defined, this indicates whether or not the instance
   property value can equal the minimum.

5.10.  maximumCanEqual

   If the maximum is defined, this indicates whether or not the instance
   property value can equal the maximum.

5.11.  minItems

   This indicates the minimum number of values in an array when an array
   is the instance value.

5.12.  maxItems

   This indicates the maximum number of values in an array when an array
   is the instance value.

5.13.  uniqueItems

   This indicates that all the items in an array must be unique (no two
   identical values) within that array when an array is the instance
   value.

5.14.  pattern

   When the instance value is a string, this provides a regular
   expression that a instance string value should match in order to be
   valid.  Regular expressions should follow the regular expression
   specification from ECMA 262/Perl 5





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5.15.  maxLength

   When the instance value is a string, this indicates maximum length of
   the string.

5.16.  minLength

   When the instance value is a string, this indicates minimum length of
   the string.

5.17.  enum

   This provides an enumeration of possible values that are valid for
   the instance property.  This should be an array, and each item in the
   array represents a possible value for the instance value.  If "enum"
   is included, the instance value must be one of the values in enum
   array in order for the schema to be valid.

5.18.  title

   This provides a short description of the instance property.  The
   value must be a string.

5.19.  description

   This provides a full description of the of purpose the instance
   property.  The value must be a string.

5.20.  format

   This property indicates the type of data, content type, or
   microformat to be expected in the instance property values.  A format
   attribute may be one of the values listed below, and if so, should
   adhere to the semantics describing for the format.  A format should
   only be used give meaning to primitive types (string, integer,
   number, or boolean).  Validators are not required to validate that
   the instance values conform to a format.  The following formats are
   defined:

      Any valid MIME media type may be used as a format value, in which
      case the instance property value must be a string, representing
      the contents of the MIME file.

      date-time - This should be a date in ISO 8601 format of YYYY-MM-
      DDThh:mm:ssZ in UTC time.  This is the recommended form of date/
      timestamp.





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      date - This should be a date in the format of YYYY-MM-DD.  It is
      recommended that you use the "date-time" format instead of "date"
      unless you need to transfer only the date part.

      time - This should be a time in the format of hh:mm:ss.  It is
      recommended that you use the "date-time" format instead of "time"
      unless you need to transfer only the time part.

      utc-millisec - This should be the difference, measured in
      milliseconds, between the specified time and midnight, January 1,
      1970 UTC.  The value should be a number (integer or float).

      regex - A regular expression.

      color - This is a CSS color (like "#FF0000" or "red").

      style - This is a CSS style definition (like "color: red;
      background-color:#FFF").

      phone - This should be a phone number (format may follow E.123).

      uri - This value should be a URI..

      email - This should be an email address.

      ip-address - This should be an ip version 4 address.

      ipv6 - This should be an ip version 6 address.

      street-address - This should be a street address.

      locality - This should be a city or town.

      region - This should be a region (a state in the US, province in
      Canada, etc.)

      postal-code - This should be a postal code (AKA zip code).

      country - This should be the name of a country.

      Additional custom formats may be defined with a URL to a
      definition of the format.

5.21.  contentEncoding

   If the instance property value is a string, this indicates that the
   string should be interpreted as binary data and decoded using the
   encoding named by this schema property.  RFC 2045, Sec 6.1 lists



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   possible values.

5.22.  default

   This indicates the default for the instance property.

5.23.  divisibleBy

   This indicates that the instance property value must be divisible by
   the given schema value when the instance property value is a number.

5.24.  disallow

   This attribute may take the same values as the "type" attribute,
   however if the instance matches the type or if this value is an array
   and the instance matches any type or schema in the array, than this
   instance is not valid.

5.25.  extends

   The value of this property should be another schema which will
   provide a base schema which the current schema will inherit from.
   The inheritance rules are such that any instance that is valid
   according to the current schema must be valid according to the
   referenced schema.  This may also be an array, in which case, the
   instance must be valid for all the schemas in the array.

6.  Hyper Schema

   This section defines hypermedia definitions of JSON schema.  The
   following attributes are specified in addition to those attributes
   that already provided by JSON schema with the specific purpose of
   informing user agents of relations between resources based on JSON
   data.  Just as with JSON schema attributes, all the attributes in
   hyper-schema are optional.  Therefore an empty object is a valid
   (non-informative) schema, and essentially describes plain JSON (no
   constraints on the structures).  Addition of attributes provides
   additive information for user agents.

6.1.  links

   The value of the links property should be an array, where each item
   in the array is a link description object which describes the link
   relations of the instances.







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6.1.1.  Link Description Object

   A link description object is used to describe the link relations.  In
   the context of a schema, it defines the link relations of the
   instances of the schema, and can be parameterized by the instance
   values.  The link description format can be used on its own in
   regular (non-schema documents), and use of this format can be
   declared by referencing the normative link description schema as the
   the schema for the data structure that uses the links.  The URI of
   the normative link description schema is:
   http://json-schema.org/links.

6.1.1.1.  href

   The value of the "href" link description property indicates the
   target URI of the related resource.  The value of the instance
   property should be resolved as a URI-Reference per [RFC3986] and may
   be a relative URI.  The base URI to be used for relative resolution
   should be the URI used to retrieve the instance object (not the
   schema) when used in the context of a schema.  Also, the URI may be
   parametrized by the property values of the instance object.

   Instance property values should be substituted into the URIs where
   matching braces ('{', '}') are found surrounding zero or more
   characters, creating an expanded URI.  Instance property value
   substitutions are resolved by using the text between the braces to
   denote the property name from the instance to get the value to
   substitute.  For example, if an href value is defined:


   http://somesite.com/{id}

   Then it would be resolved by replace the value of the "id" property
   value from the instance object.  If the value of the "id" property
   was "45", the expanded URI would be:


   http://somesite.com/45

   If matching braces are found with the string "-this" (no quotes)
   between the braces, than the actual instance value should be used to
   replace the braces, rather than a property value.  This should only
   be used in situations where the instance is a scalar (string,
   boolean, or number), and not for objects or arrays.







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6.1.1.2.  rel

   The value of the "rel" property indicates the name of the relation to
   the target resource.  The relation to the target should be
   interpreted as specifically from the instance object that the schema
   (or sub-schema) applies to, not just the top level resource that
   contains the object within its hierarchy.  If a resource JSON
   representation contains a sub object with a property interpreted as a
   link, that sub-object holds the relation with the target.  A relation
   to target from the top level resource must be indicated with the
   schema describing the top level JSON representation.

   Relationship definitions SHOULD NOT be media type dependent, and
   users are encouraged to utilize existing accepted relation
   definitions, including those in existing relation registries (see
   &rfc4287).  However, we define these relation here for clarity of
   normative interpretation within the context of JSON hyper schema
   defined relations:

      self - If the relation value is "self", when this property is
      encountered in the instance object, the object represents a
      resource and the instance object is treated as a full
      representation of the target resource identified by the specified
      URI.

      full - This indicates that the target of the link is the full
      representation for the instance object.  The object that contains
      this link may not be the full representation.

      describedby - This indicates the target of the link is the schema
      for the instance object.  This may be used to specifically denote
      the schemas of objects within a JSON object hierarchy,
      facilitating polymorphic type data structures.

      The following relations are applicable for schemas (the schema as
      the "from" resource in the relation).

      instances - This indicates the target resource that represents
      collection of instances of a schema.

      create - This indicates a target to use for creating new instances
      of a schema.  This link definition SHOULD be a submission link
      with a non-safe method (like POST).

   For example, if a schema is defined:






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

   And if a collection of instance resource's JSON representation was
   retrieved:


   GET /Resource/

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

   This would indicate that for the first item in the collection, it's
   own (self) URI would resolve to "/Resource/thing" and the first
   item's "up" relation should be resolved to the resource at
   "/Resource/parent".  The "children" collection would be located at
   "/Resource/?upId=thing".

6.1.1.2.1.  targetSchema

   This property value can be a schema that defines the expected
   structure of the JSON representation of the target of the link.







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6.1.1.3.  Submission Link Properties

   The following properties also apply to link definition objects, and
   provide functionality analogous to HTML forms, in providing a means
   for submitting extra (often user supplied) information to send to a
   server.

6.1.1.3.1.  method

   This indicates which method should be used to access the target
   resource.  In an HTTP environment, this would be "GET" or "POST"
   (other HTTP methods such as "PUT" and "DELETE" have semantics that
   are clearly implied by accessed resources, and do not need to be
   defined here).  This defaults to "GET".

6.1.1.3.2.  enctype

   If present, this property indicates a query media type format that
   the server supports for querying or posting to the collection of
   instances at the target resource.  The query can be suffixed to the
   target URI to query the collection with property-based constraints on
   the resources that SHOULD be returned from the server or used to post
   data to the resource (depending on the method).  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:


   /Product/?name=Slinky

   If no enctype or method is specified, only the single URI specified
   by the href property is defined.  If the method is POST, application/
   json is the default media type.



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6.1.1.3.3.  properties

   This is inherited from the base JSON schema definition, and can
   follow the same structure, but its meaning should be used to define
   the acceptable property names and values for the action (whether it
   be for the GET query or POST body).  If properties are omitted, and
   this form is the child of a schema, the properties from the parent
   schema should be used as the basis for the form action.

6.2.  fragmentResolution

   This property indicates the fragment resolution protocol to use for
   resolving fragment identifiers in URIs within the instance
   representations.  This applies to the instance object URIs and all
   children of the instance object's URIs.  The default fragment
   resolution protocol is "slash-delimited", which is defined below.
   Other fragment resolution protocols may be used, but are not defined
   in this document.

   The fragment identifier is based on RFC 2396 Sec 5, and defines the
   mechanism for resolving references to entities within a document.

6.2.1.  dot-delimited fragment resolution

   With the dot-delimited fragment resolution protocol, the fragment
   identifier is interpreted as a series of property reference tokens
   that are delimited by the "." character (\x2E).  Each property
   reference token is a series of any legal URI component characters
   except the "." character.  Each property reference token should be
   interpreted, starting from the beginning of the fragment identifier,
   as a path reference in the target JSON structure.  The final target
   value of the fragment can be determined by starting with the root of
   the JSON structure from the representation of the resource identified
   by the pre-fragment URI.  If the target is a JSON object, than the
   new target is the value of the property with the name identified by
   the next property reference token in the fragment.  If the target is
   a JSON array, than the target is determined by finding the item in
   array the array with the index defined by the next property reference
   token (which MUST be a number).  The target is successively updated
   for each property reference token, until the entire fragment has been
   traversed.

   Property names SHOULD be URI-encoded.  In particular, any "." in a
   property name MUST be encoded to avoid being interpreted as a
   property delimiter.

   For example, for the following JSON representation:




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   {
      "foo":{
         "anArray":[
           {"prop":44}
         ],
         "another prop":{
             "baz":"A string"
         }
      }
   }

   The following fragment identifiers would be resolved:


   fragment identifier    resolution
   -------------------    ----------
   #                      self, the root of the resource itself
   #foo                   the object referred to by the foo property
   #foo.another prop      the object referred to by the "another prop"
                          property of the object referred to by the
                          "foo" property
   #foo.another prop.baz  the string referred to by the value of "baz"
                          property of the "another prop" property of
                          the object referred to by the "foo" property
   #foo.anArray.0         the first object in the "anArray" array

6.2.2.  slash-delimited fragment resolution

   The slash-delimited fragment resolution protocol is exactly the same
   as dot-delimited fragment resolution protocol except that the "/"
   character (\x2F) is used as the delimiter between property names
   (instead of ".").

6.3.  root

   This attribute indicates that the value of the instance property
   value SHOULD be treated as the root or the body of the representation
   for the purposes of user agent interaction and fragment resolution
   (all other properties of the instance objects are can be regarded as
   meta-data descriptions for the data).

6.4.  readonly

   This indicates that the instance property should not be changed.
   Attempts by a user agent to modify the value of this property are
   expected to be rejected by a server.





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6.5.  pathStart

   This property value is a URI-Reference that indicates the URI that
   all the URIs for the instances of the schema should start with.  When
   multiple schemas have been referenced for an instance, the user agent
   can determine if this schema is applicable for a particular instance
   by determining if URI of the instance begins with the pathStart's
   referenced URI. pathStart MUST be resolved as per [RFC3986] section
   5.  If the URI of the instance does not start with URI indicated by
   pathStart, or if another schema specifies a starting URI that is
   longer and also matches the instance, this schema should not be
   applied to the instance.  Any schema that does not have a pathStart
   attribute should be considered applicable to all the instances for
   which it is referenced.

6.6.  mediaType

   This indicates the media type of the instance representations that
   this schema is defining.

6.7.  alternate

   This is an array of JSON schema definitions that define any other
   schemas for alternate JSON-based representations of the instance
   resources.

7.  Security Considerations

   This specification is a sub-type of the JSON format, and consequently
   the security considerations are generally the same as RFC 4627.
   However, an additional issue is that 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.  For example, if a hyper schema was defined:


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




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   And a resource was requested from somesite.com:


   GET /foo/

   With a response of:


Content-Type: application/json; profile=/schema-for-this-data
[
  {"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"}
]

8.  IANA Considerations

   The proposed MIME media type for JSON Schema is application/
   schema+json

   Type name: application

   Subtype name: schema+json

   Required parameters: profile

   The value of the profile parameter should be a URI (relative or
   absolute) that refers to the schema used to define the structure of
   this structure (the meta-schema).  Normally the value would be
   http://json-schema.org/hyper-schema, but it is allowable to use other
   schemas that extend the hyper schema's meta- schema.

   Optional parameters: pretty

   The value of the pretty parameter may be true or false to indicate if
   additional whitespace has been included to make the JSON
   representation easier to read.

8.1.  Registry of Link Relations

   This registry is maintained by IANA per RFC 4287 and this
   specification adds three values: "full", "create", "instances".  New



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   assignments are subject to IESG Approval, as outlined in [RFC5226].
   Requests should be made by email to IANA, which will then forward the
   request to the IESG, requesting approval.

9.  References

9.1.  Normative References

   [RFC3986]                          Berners-Lee, T., Fielding, R., and
                                      L. Masinter, "Uniform Resource
                                      Identifier (URI): Generic Syntax",
                                      STD 66, RFC 3986, January 2005.

   [RFC2119]                          Bradner, S., "Key words for use in
                                      RFCs to Indicate Requirement
                                      Levels", BCP 14, RFC 2119,
                                      March 1997.

   [RFC4287]                          Nottingham, M., Ed. and R. Sayre,
                                      Ed., "The Atom Syndication
                                      Format", RFC 4287, December 2005.

   [RFC3339]                          Klyne, G., Ed. and C. Newman,
                                      "Date and Time on the Internet:
                                      Timestamps", RFC 3339, July 2002.

   [RFC2045]                          Freed, N. and N. Borenstein,
                                      "Multipurpose Internet Mail
                                      Extensions (MIME) Part One: Format
                                      of Internet Message Bodies",
                                      RFC 2045, November 1996.

9.2.  Informative References

   [RFC4627]                          Crockford, D., "The application/
                                      json Media Type for JavaScript
                                      Object Notation (JSON)", RFC 4627,
                                      July 2006.

   [RFC2616]                          Fielding, R., Gettys, J., Mogul,
                                      J., Frystyk, H., Masinter, L.,
                                      Leach, P., and T. Berners-Lee,
                                      "Hypertext Transfer Protocol --
                                      HTTP/1.1", RFC 2616, June 1999.

   [RFC5226]                          Narten, T. and H. Alvestrand,
                                      "Guidelines for Writing an IANA
                                      Considerations Section in RFCs",



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                                      BCP 26, RFC 5226, May 2008.

   [I-D.hammer-discovery]             Hammer-Lahav, E., "LRDD: Link-
                                      based Resource Descriptor
                                      Discovery",
                                      draft-hammer-discovery-04 (work in
                                      progress), March 2010.

   [I-D.gregorio-uritemplate]         Gregorio, J., Fielding, R.,
                                      Hadley, M., and M. Nottingham,
                                      "URI Template",
                                      draft-gregorio-uritemplate-04
                                      (work in progress), March 2010.

   [I-D.nottingham-http-link-header]  Nottingham, M., "Web Linking", dra
                                      ft-nottingham-http-link-header-08
                                      (work in progress), March 2010.

   [W3C.REC-html401-19991224]         Hors, A., Jacobs, I., and D.
                                      Raggett, "HTML 4.01
                                      Specification", World Wide Web
                                      Consortium Recommendation REC-
                                      html401-19991224, December 1999, <
                                      http://www.w3.org/TR/1999/
                                      REC-html401-19991224>.

Appendix A.  Change Log

   -02

   o  Replaced maxDecimal attribute with divisibleBy attribute

   o  Added slash-delimited fragment resolution protocol and made it the
      default.

   o  Added language about using links outside of schemas by referencing
      it's normative URI.

   o  Added uniqueItems attribute

   o  Added targetSchema attribute to link description object

   -01

   o  Fixed category and updates from template

   -00




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   o  Initial draft

Appendix B.  Open Issues

   Should we give a preference to MIME headers over Link headers (or
   only use one)?

   Should we use "profile" as the media type parameter instead?

   Should "root" be a MIME parameter instead of a schema attribute?

   Should "format" be renamed to "mediaType" or "contentType" to reflect
   the usage MIME media types that are allowed.

   I still do not like how dates are handled.

   Should "slash-delimited" or "dot-delimited" be the default fragment
   resolution protocol?

Author's Address

   Kris Zyp (editor)
   SitePen (USA)
   530 Lytton Avenue
   Palo Alto, CA 94301
   USA

   Phone: +1 650 968 8787
   EMail: kris@sitepen.com






















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