One document matched: draft-zyp-json-schema-04.xml
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<rfc category="info" docName="draft-zyp-json-schema-04" ipr="trust200902">
<front>
<title abbrev="JSON Schema">JSON Schema: core definitions and terminology</title>
<author fullname="Francis Galiegue" initials="F" surname="Galiegue" role="editor">
<address>
<email>fgaliegue@gmail.com</email>
</address>
</author>
<author fullname="Kris Zyp" initials="K" surname="Zyp" role="editor">
<organization>SitePen (USA)</organization>
<address>
<postal>
<street>530 Lytton Avenue</street>
<city>Palo Alto, CA 94301</city>
<country>USA</country>
</postal>
<phone>+1 650 968 8787</phone>
<email>kris@sitepen.com</email>
</address>
</author>
<author fullname="Gary Court" initials="G" surname="Court">
<address>
<postal>
<street></street>
<city>Calgary, AB</city>
<country>Canada</country>
</postal>
<email>gary.court@gmail.com</email>
</address>
</author>
<date year="2013"/>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>JSON</keyword>
<keyword>Schema</keyword>
<keyword>Hyper Schema</keyword>
<keyword>Hypermedia</keyword>
<abstract>
<t>
JSON 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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
JSON 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.
</t>
<t>
This specification defines JSON Schema core terminology and mechanisms; related
specifications build upon this specification and define different applications of
JSON Schema.
</t>
</section>
<section title="Conventions and Terminology">
<t>
<!-- The text in this section has been copied from the official boilerplate,
and should not be modified.-->
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 <xref target="RFC2119">RFC 2119</xref>.
</t>
<t>
The terms "JSON", "JSON text", "JSON value", "member", "element", "object", "array",
"number", "string", "boolean", "true", "false", and "null" in this document are to
be interpreted as defined in <xref target="RFC4627">RFC 4627</xref>.
</t>
</section>
<section title="Core terminology">
<section title="Property, item">
<t>
When refering to a JSON Object, as defined by <xref target="RFC4627"/>, the
terms "member" and "property" may be used interchangeably.
</t>
<t>
When refering to a JSON Array, as defined by <xref target="RFC4627"/>, the terms
"element" and "item" may be used interchangeably.
</t>
</section>
<section title="JSON Schema, keywords">
<t>
A JSON Schema is a JSON document, and that document MUST be an object. Object
members (or properties) defined by JSON Schema (this specification, or related
specifications) are called keywords, or schema keywords.
</t>
<t>
A JSON Schema MAY contain properties which are not schema keywords.
</t>
</section>
<section title="Empty schema">
<t>
An empty schema is a JSON Schema with no properties, or with properties which
are not schema keywords.
</t>
</section>
<section title="Root schema, subschema">
<t>
This example of a JSON Schema has no subschemas:
</t>
<figure>
<artwork>
<![CDATA[
{
"title": "root"
}
]]>
</artwork>
</figure>
<t>
JSON Schemas can also be nested, as in this example:
</t>
<figure>
<artwork>
<![CDATA[
{
"title": "root",
"otherSchema": {
"title": "nested",
"anotherSchema": {
"title": "alsoNested"
}
}
}
]]>
</artwork>
</figure>
<t>
In this example, "nested" and "alsoNested" are subschemas, and "root" is a root
schema.
</t>
</section>
<section title="JSON Schema primitive types">
<t>
JSON Schema defines seven primitive types for JSON values:
<list style="hanging">
<t hangText="array">A JSON array.</t>
<t hangText="boolean">A JSON boolean.</t>
<t hangText="integer">A JSON number without a fraction or exponent part.</t>
<t hangText="number">Any JSON number. Number includes integer.</t>
<t hangText="null">The JSON null value.</t>
<t hangText="object">A JSON object.</t>
<t hangText="string">A JSON string.</t>
</list>
</t>
</section>
<section title="JSON value equality">
<t>
Two JSON values are said to be equal if and only if:
<list>
<t>both are nulls; or</t>
<t>both are booleans, and have the same value; or</t>
<t>both are strings, and have the same value; or</t>
<t>both are numbers, and have the same mathematical value; or</t>
<t>both are arrays, and:
<list>
<t>have the same number of items; and</t>
<t>items at the same index are equal according to this definition;
or</t>
</list>
</t>
<t>both are objects, and:
<list>
<t>have the same set of property names; and</t>
<t>values for a same property name are equal according to this
definition.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Instance">
<t>
An instance is any JSON value. An instance may be described by one or more
schemas.
</t>
<t>
An instance may also be referred to as "JSON instance", or "JSON data".
</t>
</section>
</section>
<section title="Overview">
<t>
This document proposes a new media type "application/schema+json" to identify JSON
Schema for describing JSON data. JSON Schemas are themselves written in JSON. This,
and related specifications, define keywords allowing to describe this data in terms
of allowable values, textual descriptions and interpreting relations with other
resources. The following sections are a summary of features defined by related
specifications.
</t>
<section title="Validation">
<t>
JSON Schema allows applications to validate instances, either non interactively
or interactively. For instance, an application may collect JSON data and check
that this data matches a given set of constraints; another application may use a
JSON Schema to build an interactive interface in order to collect user input
according to constraints described by JSON Schema.
</t>
</section>
<section title="Hypermedia and linking">
<t>
JSON Schema provides a method for extracting link relations from instances to
other resources, as well as describing interpretations of instances as
multimedia data. This allows JSON data to be interpreted as rich hypermedia
documents, placed in the context of a larger set of related resources.
</t>
</section>
</section>
<section title="General considerations">
<section title="Applicability to all JSON values">
<t>
It is acknowledged that an instance may be any valid JSON value as defined
by <xref target="RFC4627"/>. As such, JSON Schema does not mandate that an
instance be of a particular type: JSON Schema can describe any JSON value,
including null.
</t>
</section>
<section title="Programming language independence">
<t>
JSON Schema is programming language agnostic. The only limitations are the ones
expressed by <xref target="RFC4627"/> and those of the host programming
language.
</t>
</section>
<section title="JSON Schema and HTTP">
<t>
This specification acknowledges the role of <xref target="RFC2616">HTTP</xref>
as the dominant protocol in use on the Internet, and the wealth of
official specifications related to it.
</t>
<t>
This specification uses a subset of these specifications to recommend a set of
mechanisms, usable by this protocol, to associate JSON instances to one or more
schemas.
</t>
</section>
<section title="JSON Schema and other protocols">
<t>
JSON Schema does not define any semantics for the client-server interface for
any other protocols than HTTP. These semantics are application dependent, or
subject to agreement between the parties involved in the use of JSON Schema for
their own needs.
</t>
</section>
<section title="Mathematical integers">
<t>
It is acknowledged by this specification that some programming languages, and
their associated parsers, use different internal representations for floating
point numbers and integers, while others do not.
</t>
<t>
As a consequence, for interoperability reasons, JSON values used in the context
of JSON Schema, whether that JSON be a JSON Schema or an instance, SHOULD ensure
that mathematical integers be represented as integers as defined by this
specification.
</t>
</section>
<section title="Extending JSON Schema">
<t>
Implementations MAY choose to define additional keywords to JSON Schema. Save
for explicit agreement, schema authors SHALL NOT expect these additional
keywords to be supported by peer implementations. Implementations SHOULD ignore
keywords they do not support.
</t>
</section>
<section title="Security considerations">
<t>
Both schemas and instances are JSON values. As such, all security considerations
defined in <xref target="RFC4627">RFC 4627</xref> apply.
</t>
</section>
</section>
<section title='The "$schema" keyword'>
<section title="Purpose">
<t>
The "$schema" keyword is both used as a JSON Schema version identifier and the
location of a resource which is itself a JSON Schema, which describes any schema
written for this particular version.
</t>
<t>
This keyword MUST be located at the root of a JSON Schema. The value of this
keyword MUST be a <xref target="RFC3986">URI</xref> and a valid <xref
target="json-reference">JSON Reference</xref>; this URI MUST be both absolute
and normalized. The resource located at this URI MUST successfully describe
itself. It is RECOMMENDED that schema authors include this keyword in their
schemas.
</t>
<t>
The following values are predefined:
<list style="hanging">
<t hangText="http://json-schema.org/schema#">JSON Schema written against
the current version of the specification.</t>
<t hangText="http://json-schema.org/hyper-schema#">JSON Schema written
against the current version of the specification.</t>
<t hangText="http://json-schema.org/draft-04/schema#">JSON Schema written
against this version.</t>
<t hangText="http://json-schema.org/draft-04/hyper-schema#">JSON Schema hyperschema
written against this version.</t>
<t hangText="http://json-schema.org/draft-03/schema#"> JSON Schema written
against <xref target="json-schema-03">JSON Schema, draft v3</xref>.</t>
<t hangText="http://json-schema.org/draft-03/hyper-schema#"> JSON Schema hyperschema
written against <xref target="json-schema-03">JSON Schema, draft
v3</xref>.</t>
</list>
</t>
</section>
<section title="Customization">
<t>
When extending JSON Schema with custom keywords, schema authors SHOULD define a
custom URI for "$schema". This custom URI MUST NOT be one of the predefined
values.
</t>
</section>
</section>
<section title="URI resolution scopes and dereferencing">
<section title="Definition">
<t>
JSON Schema uses <xref target="json-reference">JSON Reference</xref> as a
mechanism for schema addressing. It extends this specification in two ways:
<list>
<t>JSON Schema offers facilities to alter the base URI against which a
reference must resolve by the means of the "id" keyword;</t>
<t>it defines a specific dereferencing mechanism extending JSON Reference to
accept arbitrary fragment parts.</t>
</list>
</t>
<t>
Altering the URI within a schema is called defining a new resolution scope. The
initial resolution scope of a schema is the URI of the schema itself, if any, or
the empty URI if the schema was not loaded from a URI.
</t>
</section>
<section title='URI resolution scope alteration with the "id" keyword'>
<section title="Valid values">
<t>
The value for this keyword MUST be a string, and MUST be a valid URI. This
URI MUST be normalized, and SHOULD NOT be an empty fragment (#) or the empty
URI.
</t>
</section>
<section title="Usage">
<t>
The "id" keyword (or "id", for short) is used to alter the resolution scope.
When an id is encountered, an implementation MUST resolve this id against
the most immediate parent scope. The resolved URI will be the new resolution
scope for this subschema and all its children, until another id is
encountered.
</t>
<t>
When using "id" to alter resolution scopes, schema authors SHOULD ensure
that resolution scopes are unique within the schema.
</t>
<t>
This schema will be taken as an example:
</t>
<!--
FIXME: http again as a scheme, maybe another one? It can be any scheme after
all
-->
<figure>
<artwork>
<![CDATA[
{
"id": "http://x.y.z/rootschema.json#",
"schema1": {
"id": "#foo"
},
"schema2": {
"id": "otherschema.json",
"nested": {
"id": "#bar"
},
"alsonested": {
"id": "t/inner.json#a"
}
},
"schema3": {
"id": "some://where.else/completely#"
}
}
]]>
</artwork>
</figure>
<t>
Subschemas at the following URI-encoded <xref target="json-pointer">JSON
Pointer</xref>s (starting from the root schema) define the following
resolution scopes:
<list style="hanging">
<t hangText="# (document root)">http://x.y.z/rootschema.json#</t>
<t hangText="#/schema1">http://x.y.z/rootschema.json#foo</t>
<t hangText="#/schema2">http://x.y.z/otherschema.json#</t>
<t hangText="#/schema2/nested">http://x.y.z/otherschema.json#bar</t>
<t hangText="#/schema2/alsonested">http://x.y.z/t/inner.json#a</t>
<t hangText="#/schema3">some://where.else/completely#</t>
</list>
</t>
</section>
<section title="Canonical dereferencing and inline dereferencing">
<t>
When resolving a URI against a resolution scope, an implementation may
choose two modes of operation:
<list style="hanging">
<t hangText="canonical dereferencing">The implementation dereferences
all resolved URIs.</t>
<t hangText="inline dereferencing">The implementation chooses to
dereference URIs within the schema.</t>
</list>
</t>
<t>
Implementations MUST support canonical dereferencing, and MAY support inline
dereferencing.
</t>
<t>
For example, consider this schema:
</t>
<figure>
<artwork>
<![CDATA[
{
"id": "http://my.site/myschema#",
"definitions": {
"schema1": {
"id": "schema1",
"type": "integer"
},
"schema2", {
"type": "array",
"items": { "$ref": "schema1" }
}
}
}
]]>
</artwork>
</figure>
<t>
When an implementation encounters the "schema1" reference, it resolves it
against the most immediate parent scope, leading to URI
"http://my.site/schema1#". The way to process this URI will differ
according to the chosen dereferencing mode:
<list>
<t>if canonical dereferencing is used, the implementation will
dereference this URI, and fetch the content at this URI;</t>
<t>if inline dereferencing is used, the implementation will notice that
URI scope "http://my.site/schema1#" is already defined within the
schema, and choose to use the appropriate subschema.</t>
</list>
</t>
</section>
<section title="Inline dereferencing and fragments">
<t>
When using inline dereferencing, a resolution scope may lead to a URI which
has a non empty fragment part which is not a JSON Pointer, as in this
example:
</t>
<figure>
<artwork>
<![CDATA[
{
"id": "http://some.site/schema#",
"not": { "$ref": "#inner" },
"definitions": {
"schema1": {
"id": "#inner",
"type": "boolean"
}
}
}
]]>
</artwork>
</figure>
<t>
An implementation choosing to support inline dereferencing SHOULD be able to
use this kind of reference. Implementations choosing to use canonical
dereferencing, however, are not required to support it.
</t>
</section>
</section>
<section title="Interoperability considerations">
<t>
Inline dereferencing can produce canonical URIs which differ from the canonical URI
of the root schema. Schema authors SHOULD ensure that implementations using
canonical dereferencing obtain the same content as implementations using inline
dereferencing.
</t>
<t>
Extended JSON References using fragments which are not JSON Pointers are not
dereferenceable by implementations choosing not to support inline dereferencing.
This kind of reference is defined for backwards compatibility, and SHOULD NOT be
used in new schemas.
</t>
</section>
</section>
<section title="Recommended correlation mechanisms for use with the HTTP protocol">
<t>
It is acknowledged by this specification that the majority of interactive JSON
Schema processing will be over HTTP. This section therefore gives recommendations
for materializing an instance/schema correlation using mechanisms currently
available for this protocol. An instance is said to be described by one (or more)
schema(s).
</t>
<section title='Correlation by means of the "Content-Type" header'>
<t>
It is RECOMMENDED that a MIME type parameter by the name of "profile" be
appended to the "Content-Type" header of the instance being processed. If
present, the value of this parameter MUST be a valid URI, and this URI SHOULD
resolve to a valid JSON Schema. The MIME type MUST be "application/json", or any
other subtype.
</t>
<t>
An example of such a header would be:
</t>
<figure>
<artwork>
<![CDATA[
Content-Type: application/my-media-type+json;
profile=http://example.com/my-hyper-schema#
]]>
</artwork>
</figure>
</section>
<section title='Correlation by means of the "Link" header'>
<t>
When using the "Link" header, the relation type used MUST be "describedBy", as
defined by <xref target="RFC5988">RFC 5988, section 5.3</xref>. The target URI
of the "Link" header MUST be a valid JSON Schema.
</t>
<t>
An example of such a header would be:
</t>
<figure>
<artwork>
<![CDATA[
Link: <http://example.com/my-hyper-schema#>; rel="describedBy"
]]>
</artwork>
</figure>
</section>
</section>
<section title="IANA Considerations">
<t>
The proposed MIME media type for JSON Schema is defined as follows:
<list>
<t>type name: application;</t>
<t>subtype name: schema+json.</t>
</list>
</t>
</section>
</middle>
<back>
<!-- References Section -->
<references title="Normative References">
&RFC2119;
</references>
<references title="Informative References">
&RFC2616;
&RFC3986;
&RFC4627;
&RFC5988;
<reference anchor="json-reference"
target="http://tools.ietf.org/html/draft-pbryan-zyp-json-ref-03">
<front>
<title>JSON Reference (work in progress)</title>
<author initials="P." surname="Bryan">
<organization>ForgeRock US, Inc.</organization>
</author>
<author initials="K." surname="Zyp">
<organization>SitePen (USA)</organization>
</author>
<date year="2012" month="September"/>
</front>
</reference>
<reference anchor="json-pointer"
target="http://tools.ietf.org/html/draft-ietf-appsawg-json-pointer-07">
<front>
<title>JSON Pointer (work in progress)</title>
<author initials="P." surname="Bryan">
<organization>ForgeRock US, Inc.</organization>
</author>
<author initials="K." surname="Zyp">
<organization>SitePen (USA)</organization>
</author>
<date year="2012" month="September"/>
</front>
</reference>
<reference anchor="json-schema-03"
target="http://tools.ietf.org/html/draft-zyp-json-schema-03">
<front>
<title>JSON Schema, draft 3</title>
<author initials="G." surname="Court">
<organization/>
</author>
<author initials="K." surname="Zyp">
<organization>SitePen (USA)</organization>
</author>
<date year="2012" month="September"/>
</front>
</reference>
</references>
<section title="ChangeLog">
<t>
<list style="hanging">
<t hangText="draft-00">
<list style="symbols">
<t>Initial draft.</t>
<t>Salvaged from draft v3.</t>
<t>Mandate the use of JSON Reference, JSON Pointer.</t>
<t>Define the role of "id". Define URI resolution scope.</t>
<t>Add interoperability considerations.</t>
</list>
</t>
</list>
</t>
</section>
</back>
</rfc>
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