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