{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "definitions": {
        "CDAIdentifier": {
            "type": "object",
            "additionalProperties": true,
            "properties": {
                "root": {
                    "type": [
                        "string",
                        "null"
                    ],
                    "minLength": 0,
                    "title": "root schema."
                },
                "extension": {
                    "type": [
                        "string",
                        "null"
                    ],
                    "minLength": 0,
                    "title": "extension schema."
                }
            }
        }
    },
    "properties": {
        "CDAIdentifier": {
            "$ref": "#/definitions/CDAIdentifier"
        }
    },
    "required": [
        "CDAIdentifier"
    ]
}