{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "definitions": {
        "advertisement": {
            "type": "object",
            "properties": {
                "id": {
                    "type": "string"
                }
            },
            "required": [
                "id"
            ]
        }
    },
    "type": "array",
    "items": {
        "$ref": "#/definitions/advertisement"
    },
    "additionalProperties": false
}