;; KIF version of the ontology from
;; Russell and Norvig, (1995), "Artificial Intelligence: A Modern Approach"

(subclass-of AbstractObjects Anything)
(subclass-of Events Anything)
(subclass-of Sets AbstractObjects)
(subclass-of Numbers AbstractObjects)
(subclass-of RepresentationalObjects AbstractObjects)
(subclass-of Sets Categories)
(subclass-of Sentences RepresentationalObjects)
(subclass-of Measurements RepresentationalObjects)
(subclass-of Times Measurements)
(subclass-of Weights Measurements)
(subclass-of Intervals Events)
(subclass-of Places Events)
(subclass-of PhysicalObjects Events)
(subclass-of Processes Events)
(subclass-of Movements Intervals)
(subclass-of Things PhysicalObjects)
(subclass-of Stuff PhysicalObjects)
(subclass-of Animals Things)
(subclass-of Agents Things)
(subclass-of Solid Stuff)
(subclass-of Liquid Stuff)
(subclass-of Gas Stuff)
(subclass-of Humans Animals)
(subclass-of Humans Agents)

(deffunction Start (?ev) :=
  (Event ?ev))

(deffunction End (?ev) :=
  (Event ?ev))

(defrelation Meet (?i ?j) :=
  (forall (?i ?j)
    (and
      (Event ?i)
      (Event ?j)
      (<=>
        (Meet ?i ?j)
        (= (Start ?i) (End ?j))))))

(defrelation Before (?i ?j) :=
  (forall (?i ?j)
    (and
      (Event ?i)
      (Event ?j)
      (<=>
        (Before ?i ?j)
        (< (End ?i) (Start ?j))))))

(defrelation After (?i ?j) :=
  (forall (?i ?j)
    (and
      (Event ?i)
      (Event ?j)
      (<=>
        (After ?i ?j)
        (Before ?j ?i)))))

(defrelation During (?i ?j) :=
  (forall (?i ?j)
    (and
      (Event ?i)
      (Event ?j)
      (<=>
        (During ?i ?j)
        (and
          (<= (Start ?j) (Start ?i))
          (<= (End ?i) (End ?j)))))))

(defrelation Overlap (?i ?j) :=
  (forall (?i ?j)
    (and
      (Event ?i)
      (Event ?j)
      (<=>
        (Overlap ?i ?j)
        (exists (?k)
          (and
            (During ?k ?i)
            (During ?k ?j)))))))