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A schema is represented in JSON by one of:

• A JSON string, naming a defined type.
• A JSON object, of the form: {"type": "typeName" ...attributes...}, where typeName is either a primitive or a derived type name, as defined below. 
• A JSON array, representing a union of embedded types.

A WSO2 ESB Data Mapper schema should start with the $schema attribute with the WSO2 Data Mapper schema version. For example: { “$schema”:”http://wso2-data-mapper-json-schema/1.0v”}

Also, it can contain following optional attributes that will define more information about the schema.

• “id”: a JSON string declaring a unique identifier for the schema.
• “title”: a JSON string defining the root element name.
• “description”: a JSON string providing a detailed description about the schema.
• “type”: a JSON string providing the element type.
• “namespaces”: a JSON array of JSON objects defining namespaces and prefix values used in the schema as shown in the following example.
  
  

{ “$schema” : ”http://wso2-data-mapper-json-schema/1.0v”,
“id”:”http://wso2-data-mapper-json-schema-sample-o1”,
“title”:”RootElement”,
"type":"object",
“description”:”This schema represent any form of object without any restriction” ,
"namespaces":[
{ "prefix":"ns1", "url":"http://ns1.com"},
{"prefix":"ns2", "url":"http://ns2.com"}]
}

Primitive types

Primitive types have no specified attributes. The set of primitive type names are as follows.

• null: no value
• boolean: a binary value
• integer: integer value
• number: rational numbers
• string: unicode character sequence

Primitive type names are also defined type names. Thus, for example, the schema "string" is equivalent to: {"type": "string"}

Complex types

WSO2 ESB Data Mapper schema supports the following complex types: object and array. 

Object

Object uses the type name “object”, and supports the following attributes.

• “id” : a JSON string declaring a unique identifier for the object (required).
• “type”: a JSON string providing the element type.
• “description”: a JSON string providing documentation to the user of this schema.
• “properties”: a JSON object listing fields (required). Each field is a JSON object.
• “attributes”: a JSON object listing XML attribute fields. Each field is a JSON object.

Arrays

For example, an array of an object containing a field named firstname is declared as shown below.

{
"type": "array", 
"items": [
{
           	"id":"http://jsonschema.net/employee/0",
           	"type":"object",
           	"properties":{
“firstname":{
                 	"id":"http://jsonschema.net/employee/0/firstname",
                 	"type":"string"
              	}
}
}]
}

Defining WSO2 schemas to Represent XML Payload