{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "definitions": {
        "simple-extension": {
            "type": "object",
            "properties": {
                "url": {
                    "type": "string"
                },
                "value": {
                    "type": "string"
                }
            }
        },
        "complex-extension": {
            "items": {
                "type": "object",
                "properties": {
                    "extension": {
                        "$ref": "#/definitions/simple-extension"
                    }
                }
            }
        }
    },
    "properties": {
        "simple-extension": {
            "$ref": "#/definitions/simple-extension"
        },
        "complex-extension.items": {
            "$ref": "#/definitions/complex-extension/items"
        }
    },
    "required": [
        "simple-extension",
        "complex-extension.items"
    ]
}