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Update Schema Object #894

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Feb 22, 2017
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Update Schema Object #894

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61ac60c
Updated Schema Object
webron Feb 21, 2017
7648c72
MOAR updates
webron Feb 21, 2017
f459807
MOAR updates
webron Feb 22, 2017
3fc3a6c
Complete rework of JSON Reference
webron Feb 22, 2017
7d0ae2d
Even MOAR changes
webron Feb 22, 2017
5b64060
Hopefully last updates
webron Feb 22, 2017
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93 changes: 50 additions & 43 deletions versions/3.0.md
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Expand Up @@ -144,14 +144,15 @@ By convention, the OpenAPI Specification (OAS) file is named `openapi.json` or `

### Data Types

Primitive data types in the OAS are based on the types supported by the [JSON-Schema Draft 4](http://json-schema.org/latest/json-schema-core.html#anchor8).
Models are described using the [Schema Object](#schemaObject) which is a subset of JSON Schema Draft 4.
Primitive data types in the OAS are based on the types supported by the [JSON Schema Specification Wright Draft 00](https://tools.ietf.org/html/draft-wright-json-schema-00#section-4.2). Note that `integer` as a type is also supported and is defined as a JSON number without a fraction or exponent part. `null` is not supported as a value.
Models are described using the [Schema Object](#schemaObject) which is an extended subset of JSON Schema Specification Wright Draft 00.

<a name="dataTypeFormat"></a>Primitives have an optional modifier property `format`.
OAS uses several known formats to more finely define the data type being used.
However, the `format` property is an open `string`-valued property, and can have any value to support documentation needs.
Formats such as `"email"`, `"uuid"`, etc., can be used even though they are not defined by this specification.
Types that are not accompanied by a `format` property follow their definition from the JSON Schema.
Types that are not accompanied by a `format` property follow their definition from the JSON Schema. Tools that do not recognize a specific `format` MAY default back to the `type` alone, as if the `format` was not specified.

The formats defined by the OAS are:


Expand Down Expand Up @@ -2211,27 +2212,29 @@ definitions:

#### <a name="referenceObject"></a>Reference Object

A simple object to allow referencing other definitions in the specification.
It can be used to reference parameters and responses that are defined at the top level for reuse.
A simple object to allow referencing other definitions in the specification, internally and externally.

The Reference Object is defined by [JSON Reference](https://tools.ietf.org/html/draft-pbryan-zyp-json-ref-03) and follows the same structure, behavior and rules.

The Reference Object is a [JSON Reference](http://tools.ietf.org/html/draft-pbryan-zyp-json-ref-02) that uses a [JSON Pointer](http://tools.ietf.org/html/rfc6901) as its value.
For this specification, only [canonical dereferencing](http://json-schema.org/latest/json-schema-core.html#anchor27) is supported.
For this specification, reference resolution is done as defined by the JSON Reference specification and not by the JSON Schema specification.

##### Fixed Fields
Field Name | Type | Description
---|:---:|---
<a name="referenceRef"></a>$ref | `string` | **Required.** The reference string.

This object cannot be extended with additional properties and any properties added SHALL be ignored.

##### Reference Object Example

```json
{
"$ref": "#/definitions/Pet"
"$ref": "#/components/definitions/Pet"
}
```

```yaml
$ref: '#/definitions/Pet'
$ref: '#/components/definitions/Pet'
```

##### Relative Schema File Example
Expand All @@ -2242,7 +2245,7 @@ $ref: '#/definitions/Pet'
```

```yaml
$ref: 'Pet.yaml'
$ref: Pet.yaml
```

##### Relative Files With Embedded Schema Example
Expand All @@ -2253,25 +2256,21 @@ $ref: 'Pet.yaml'
```

```yaml
$ref: 'definitions.yaml#/Pet'
$ref: definitions.yaml#/Pet
```

#### <a name="schemaObject"></a>Schema Object

The Schema Object allows the definition of input and output data types.
These types can be objects, but also primitives and arrays.
This object is based on the [JSON Schema Specification Draft 4](http://json-schema.org/) and uses a predefined subset of it.
On top of this subset, there are extensions provided by this specification to allow for more complete documentation.
This object is an extended subset of the [JSON Schema Specification Wright Draft 00](http://json-schema.org/).

Further information about the properties can be found in [JSON Schema Core](http://json-schema.org/latest/json-schema-core.html) and [JSON Schema Validation](http://json-schema.org/latest/json-schema-validation.html).
Further information about the properties can be found in [JSON Schema Core](https://tools.ietf.org/html/draft-wright-json-schema-00) and [JSON Schema Validation](https://tools.ietf.org/html/draft-wright-json-schema-validation-00).
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Here you call it "JSON Schema Core" but you reference it earlier as "JSON Schema Specification Wright Draft 00". Make a decision and use it in both places.

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JSON Schema is split into two specifications - Core and Validation. Can't keep it as one, and shouldn't reference both every single time.

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Fair enough.

Unless stated otherwise, the property definitions follow the JSON Schema specification as referenced here.

The following properties are taken directly from the JSON Schema definition and follow the same specifications:
- $ref - As a [JSON Reference](https://tools.ietf.org/html/draft-pbryan-zyp-json-ref-03)
- format (See [Data Type Formats](#dataTypeFormat) for further details)

- title
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remove parens here (not used elsewhere in OAS when describing CommonMark)

- description ([CommonMark syntax](http://spec.commonmark.org/) can be used for rich text representation)
- default (Unlike JSON Schema, the value MUST conform to the defined type for the Schema Object)
- multipleOf
- maximum
- exclusiveMaximum
Expand All @@ -2287,25 +2286,33 @@ The following properties are taken directly from the JSON Schema definition and
- minProperties
- required
- enum
- type

The following properties are taken from the JSON Schema definition but their definitions were adjusted to the OpenAPI Specification.
Their definition is the same as the one from JSON Schema, only where the original definition references the JSON Schema definition, the [Schema Object](#schemaObject) definition is used instead.
- items
- allOf
- oneOf
- anyOf
- not
- properties
- additionalProperties

The following properties are taken from the JSON Schema definition but their definitions were adjusted to the OpenAPI Specification.
- type - Value MUST be a string. Multiple types via an array are not supported.
- allOf - Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.
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Should this be:
"MUST be of a Schema Object or Schema Reference" ? (Ditto on the other items in the list.

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Please elaborate on what "not a standard JSON Schema." means. However, if it means "not a full JSON Schema but the OpenAPI Specification schema", I think we should just drop this since you already refer explicitly to [Schema Object](#schemaObject)

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It should be the Schema Object, not Schema Reference (which I assume you meant JSON Reference). The Schema Object contains the JSON Reference in it.

The 'standard JSON Schema' is in reference to the initial point that the Schema Object is an extended subset of JSON Schema. I'd rather keep this explicit here due to questions raised in the past.

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@whitlockjc whitlockjc Feb 22, 2017 •
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@DavidBiesack I almost responded with a "+1" to your comment but I think the "Inline or referenced schema" as to being either a Schema Object or a JSON Reference to a Schema Object defined elsewhere. @webron's wording seem fine to me.

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I still think "not a standard JSON Schema" may be confusing and not needed -- it just raises questions and distracts from the spec. Better IMHO would be to remove it or as @whitlockjc suggests, add "or a or a JSON Reference to a Schema Object" (I don't thing "defined elsewhere" is needed; that is implicit in being a JSON References - concise is better)

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I think it is useful to remind people that even when embedding schema objects in allOf what is being embedded is not a regular JSON Schema. I suspect many people don't realize that the schemas inside OpenAPI are not regular JSON Schemas.

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Doesn't linking to a Schema Object do this?

- oneOf - Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.
- anyOf - Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.
- not - Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.
- items - Value MUST be an object and not an array. Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema. `items` MUST be present if the `type` is `array`.
- properties - Property definitions MUST be a [Schema Object](#schemaObject) and not a standard JSON Schema (inline or referenced).
- additionalProperties - Value can be boolean or object. Inline or referenced schema MUST be of a [Schema Object](#schemaObject) and not a standard JSON Schema.
- description - [CommonMark syntax](http://spec.commonmark.org/) can be used for rich text representation.
- format - See [Data Type Formats](#dataTypeFormat) for further details. While relying on JSON Schema's defined formats, the OAS offers a few additional predefined formats.
- default - The default value represents what would be assumed by the consumer of the input as the value of the schema if one is not provided. Unlike JSON Schema, the value MUST conform to the defined type for the Schema Object defined at the same level. For example, of `type` is `string`, then `default` can be `"foo"`` but cannot be `1`.

Alternatively, any time a Scheme Object can be used, a [Reference Object](#referenceObject) can be used in its place. This allows referencing definitions in place of defining them inline.

Additional properties defined by the JSON Schema specification that are not mentioned here are strictly unsupported.

Other than the JSON Schema subset fields, the following fields may be used for further schema documentation.

##### Fixed Fields
Field Name | Type | Description
---|:---:|---
<a name="schemaDiscriminator"></a>discriminator | `string` | Adds support for polymorphism. The discriminator is the schema property name that is used to differentiate between other schema that inherit this schema. The property name used MUST be defined at this schema and it MUST be in the `required` property list. When used, the value MUST be the name of this schema or any schema that inherits it.
<a name="schemaReadOnly"></a>readOnly | `boolean` | Relevant only for Schema `"properties"` definitions. Declares the property as "read only". This means that it MAY be sent as part of a response but MUST NOT be sent as part of the request. Properties marked as `readOnly` being `true` SHOULD NOT be in the `required` list of the defined schema. Default value is `false`.
<a name="schemaNullable"></a>nullable | `boolean` | Allows sending a `null` value for the defined schema. Default value is `false`.
<a name="schemaDiscriminator"></a>discriminator | `string` | Adds support for polymorphism. The discriminator is the schema property name that is used to differentiate between other schema that inherit this schema. The property name used MUST be defined at this schema and it MUST be in the `required` property list. When used, the value MUST be the name of this schema or any schema that inherits it. See [Composition and Inheritance](#schemaComposition) for more details.
<a name="schemaReadOnly"></a>readOnly | `boolean` | Relevant only for Schema `"properties"` definitions. Declares the property as "read only". This means that it MAY be sent as part of a response but SHOULD NOT be sent as part of the request. If property is marked as `readOnly` being `true` and is in the `required` list, the `required` will take effect on the response only. A property MUST NOT be marked as both `readOnly` and `writeOnly` being `true`. Default value is `false`.
<a name="schemaWriteOnly"></a>writeOnly | `boolean` | Relevant only for Schema `"properties"` definitions. Declares the property as "write only". This means that it MAY be sent as part of a request but SHOULD NOT be sent as part of the response. If property is marked as `writeOnly` being `true` and is in the `required` list, the `required` will take effect on the request only. A property MUST NOT be marked as both `readOnly` and `writeOnly` being `true`. Default value is `false`.
<a name="schemaXml"></a>xml | [XML Object](#xmlObject) | This MAY be used only on properties schemas. It has no effect on root schemas. Adds Additional metadata to describe the XML representation format of this property.
<a name="schemaExternalDocs"></a>externalDocs | [External Documentation Object](#externalDocumentationObject) | Additional external documentation for this schema.
<a name="schemaExample"></a>example | Any | A free-form property to include an example of an instance for this schema.
Expand All @@ -2314,7 +2321,7 @@ Field Name | Type | Description

This object can be extended with [Specification Extensions](#specificationExtensions).

###### Composition and Inheritance (Polymorphism)
###### <a name="schemaComposition"></a>Composition and Inheritance (Polymorphism)

The OpenAPI Specification allows combining and extending model definitions using the `allOf` property of JSON Schema, in effect offering model composition.
`allOf` takes in an array of object definitions that are validated *independently* but together compose a single object.
Expand All @@ -2323,7 +2330,9 @@ While composition offers model extensibility, it does not imply a hierarchy betw
To support polymorphism, OpenAPI Specification adds the support of the `discriminator` field.
When used, the `discriminator` will be the name of the property used to decide which schema definition is used to validate the structure of the model.
As such, the `discriminator` field MUST be a required field.
The value of the chosen property has to be the friendly name given to the model under the `definitions` property.
There are are two ways to define the value of a discriminator for an inheriting instance.
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Without an example, this portion is unclear to me.

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Actually, I might get this. Are you saying that the value of the discriminator field must match the name of a definition? Does this mean you can only use values that match keys of #/components/definitions?

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Good point -- we rely heavily on external schema files via $ref. For example, if Cat and Dog are defined externally, I should still be able to use them. However for a schema included from an external schema.json there is no name as there is for one defined in /components/definitions. If all three schema (Pet, Cat, Doc) were defined externally (so that they can be used in multiple OpenAPI documents) and there is no single /components/definitions in which they reside, how would this work?

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We'll be handling the discriminator in a separate PR.

- Use the definition's name.
- Override the definition's name by overriding the property with a new value. If exists, this takes precedence over the definition's name.
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I'm not sure what this means. Override which property - the discriminator field (petType in this example)? If so, how is it overridden and specified? Would I do:

  Cat:  ## "Cat" will be used as the discriminator value
    description: A representation of a cat
    allOf:
    - $ref: '#/definitions/Pet'
    - type: object
      properties:
         petType:
              type: string
              enum:
              - Cat
          huntingSkill:
             ...

An example would help.

As such, inline schema definitions, which do not have a given id, *cannot* be used in polymorphism.

###### XML Modeling
Expand All @@ -2335,8 +2344,6 @@ The [XML Object](#xmlObject) contains additional information about the available

###### Primitive Sample

Unlike previous versions of Swagger, OpenAPI Schema definitions can be used to describe primitive and arrays as well.

```json
{
"type": "string",
Expand All @@ -2362,7 +2369,7 @@ format: email
"type": "string"
},
"address": {
"$ref": "#/definitions/Address"
"$ref": "#/components/definitions/Address"
},
"age": {
"type": "integer",
Expand All @@ -2381,7 +2388,7 @@ properties:
name:
type: string
address:
$ref: '#/definitions/Address'
$ref: '#/components/definitions/Address'
age:
type: integer
format: int32
Expand Down Expand Up @@ -2413,15 +2420,15 @@ For a string to model mapping:
{
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/ComplexModel"
"$ref": "#/components/definitions/ComplexModel"
}
}
```

```yaml
type: object
additionalProperties:
$ref: '#/definitions/ComplexModel'
$ref: '#/components/definitions/ComplexModel'
```

###### Model with Example
Expand Down Expand Up @@ -2599,7 +2606,7 @@ definitions:
]
},
"Cat": {
"description": "A representation of a cat",
"description": "A representation of a cat. Note that `Cat` will be used as the discriminator value.",
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Please add an example:

Below are examples showing an array of Pet objects using petType as a discriminator:

- name: "Fluffy"
  petType: "Cat"
  huntingSkill: "lazy"
- name: "Rover"
  petType: "Dog"
  packSize: 6
[
  {
    "name" : "Fluffy",
    "petType" : "Cat",
    "huntingSkill" : "lazy"
  },
  {
    "name" : "Rover",
    "petType" : "Dog",
    "packSize" : 6
  }
]

"allOf": [
{
"$ref": "#/definitions/Pet"
Expand All @@ -2626,7 +2633,7 @@ definitions:
]
},
"Dog": {
"description": "A representation of a dog",
"description": "A representation of a dog. Note that `Dog` will be used as the discriminator value.",
"allOf": [
{
"$ref": "#/definitions/Pet"
Expand Down Expand Up @@ -2665,7 +2672,7 @@ definitions:
required:
- name
- petType
Cat:
Cat: ## "Cat" will be used as the discriminator value
description: A representation of a cat
allOf:
- $ref: '#/definitions/Pet'
Expand All @@ -2682,7 +2689,7 @@ definitions:
- aggressive
required:
- huntingSkill
Dog:
Dog: ## "Dog" will be used as the discriminator value
description: A representation of a dog
allOf:
- $ref: '#/definitions/Pet'
Expand Down