JSON – Schema:

      JSON Schema is a specification for JSON based format for defining the structure of JSON data. It was written under IETF draft which expired in 2011. JSON Schema −

• Describes your existing data format.
• Clear, human- and machine-readable documentation.
• Complete structural validation, useful for automated testing.
• Complete structural validation, validating client-submitted data.

-                    JSON Schema Validation Libraries:

There are several validators currently available for different programming languages. Currently the most complete and compliant JSON Schema validator available is JSV.

Languages	Libraries
C	WJElement (LGPLv3)
Java	json-schema-validator (LGPLv3)
.NET	Json.NET (MIT)
ActionScript 3	Frigga (MIT)
Haskell	aeson-schema (MIT)
Python	Jsonschema
Ruby	autoparse (ASL 2.0); ruby-jsonschema (MIT)
PHP	php-json-schema (MIT). json-schema (Berkeley)
JavaScript	Orderly (BSD); JSV; json-schema; Matic (MIT); Dojo; Persevere (modified BSD or AFL 2.0); schema.js.

-                    JSON Schema Example:

Given below is a basic JSON schema, which covers a classical product catalog description –

{

"$schema":"http://json-schema.org/draft-04/schema#",

"title":"Product",

"description":"A product from Acme's catalog",

"type":"object",

"properties":{

"id":{

"description":"The unique identifier for a product",

"type":"integer"

},

"name":{

"description":"Name of the product",

"type":"string"

},

"price":{

"type":"number",

"minimum":0,

"exclusiveMinimum":true
}
},
         
"required":["id","name","price"]
}


Let's the check various important keywords that can be used
in this schema –

 


  

  

S. No.

  

  

Keyword &
  Description

 

  

  

1

  

  

$schema

The $schema keyword states that this
  schema is written according to the draft v4 specification.

 

  

  

2

  

  

title

You will use this to give a title to
  your schema.

 

  

  

3

  

  

description

A little description of the schema.

 

  

  

4

  

  

type

The type keyword defines the first
  constraint on our JSON data: it has to be a JSON Object.

 

  

  

5

  

  

properties

Defines various keys and their value
  types, minimum and maximum values to be used in JSON file.

 

  

  

6

  

  

required

This keeps a list of required
  properties.

 

  

  

7

  

  

minimum

This is the constraint to be put on the
  value and represents minimum acceptable value.

 

  

  

8

  

  

exclusiveMinimum

If "exclusiveMinimum" is
  present and has boolean value true, the instance is valid if it is strictly
  greater than the value of "minimum".

 

  

  

9

  

  

maximum

This is the constraint to be put on the
  value and represents maximum acceptable value.

 

  

  

10

  

  

exclusiveMaximum

If "exclusiveMaximum" is
  present and has boolean value true, the instance is valid if it is strictly
  lower than the value of "maximum".

 

  

  

11

  

  

multipleOf

A numeric instance is valid against
  "multipleOf" if the result of the division of the instance by this
  keyword's value is an integer.

 

  

  

12

  

  

maxLength

The length of a string instance is
  defined as the maximum number of its characters.

 

  

  

13

  

  

minLength

The length of a string instance is
  defined as the minimum number of its characters.

 

  

  

14

  

  

pattern

A string instance is considered valid if
  the regular expression matches the instance successfully.

 


You can check a http://json-schema.org for the complete list of keywords that can be used in
defining a JSON schema. The above schema can be used to test the validity of
the following JSON code −

[
{
"id":2,
"name":"An ice sculpture",
"price":12.50,
},
         
{
"id":3,
"name":"A blue mouse",
"price":25.50,
}
]