An O-O frame example:


(FRAME        vehicle ... )
            
(FRAME        truck    
 ISA          vehicle            ; inherits from "FRAME vehicle"
 WEIGHT       (TYPE wtmeasure)
 CAPACITY     (TYPE volmeasure)
 NUMWHEELS    (TYPE integer))

(FRAME        trailertruck
 ISA          truck              ; inherits from "FRAME truck"
 PART         (TYPE trailer)
 NUMWHEELS    18)                ; default

(FRAME        truck17
 INST         trailertruck       ; inherits from "FRAME trailertruck"
 WEIGHT       2000
 CAPACITY     1000
 COLOR        red
 NUMWHEELS    16)                ; specific vals override generic