{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "allOf": [
    {
      "$ref":"#/definitions/yesno"
    }
  ],
  "definitions": {
    "yesno": {
      "type": "string",
      "enum": [
        "yes",
        "no"
      ]
    }
  }
}