{
    "properties" : {
        "event" : {
            "properties" : {
                "category" : {
                    "type" : "keyword"
                }
            }
        },
        "@timestamp" : {
            "type" : "date"
        },
        "serial_event_id" : {
            "type" : "long"
        },
        "parent_child" : {
            "type" : "join",
            "relations" : {
                "question" : "answer"
            }
        }
    }
}