scratch.clj

(require '[clojure.set :as set])


(def info
  [{:year 2017
    :month 4
    :data "x"}
   {:year 2017
    :month 4
    :data "y"}
   {:year 2017
    :month 7
    :data "z"}])


(def db (reduce
         (fn [db fact]
           (merge-with into db
                       (set/index [fact] [:entity])
                       (set/index [fact] [:entity :attribute])
                       (set/index [fact] [:entity :attribute :value])
                       (set/index [fact] [:attribute])
                       (set/index [fact] [:attribute :value])
                       (set/index [fact] [:value])))
         {}
         (for [m info
               :let [id (java.util.UUID/randomUUID)]
               [k v] m]
           {:entity id
            :attribute k
            :value v})))

(for [{:keys [entity attribute value]} (get db {:attribute :month :value 4})
      {data :value} (get db {:entity entity :attribute :data})]
  [entity data])


;;=> ([#uuid "8ce5aaea-e633-4972-b8ef-3202680b2f6f" "y"] [#uuid "08d3e0ec-c08b-492e-b638-86fb2e932a93" "x"])