▁and ▁" what ▁is ▁the ▁nature ▁of ▁reality ? ". ▁One ▁of ▁five ▁traditional ▁branches ▁of ▁philosophy , ▁met aph ys ics , ▁is ▁concerned ▁with ▁expl oring ▁existence ▁through ▁properties , ▁entities ▁and ▁relations ▁such ▁as ▁those ▁between ▁particular s ▁and ▁univers als , ▁intr insic ▁and ▁extr insic ▁properties , ▁or ▁ess ence ▁and ▁existence . ▁Met aph ys ics ▁has ▁been ▁an ▁on going ▁topic ▁of ▁discussion ▁since ▁recorded ▁history . ▁ ▁Since ▁the ▁mid - 1 9 7 0 s , ▁research ers ▁in ▁the ▁field ▁of ▁artificial ▁intelligence ▁( AI ) ▁have ▁recognized ▁that ▁knowledge ▁engineering ▁is ▁the ▁key ▁to ▁building ▁large ▁and ▁powerful ▁A I ▁systems . ▁A I ▁research ers ▁argued ▁that ▁they ▁could ▁create ▁new ▁ont ologies ▁as ▁computational ▁models ▁that ▁enable ▁certain ▁kinds ▁of ▁autom ated ▁reasoning , ▁which ▁was ▁only ▁margin ally ▁successful . ▁In ▁the ▁ 1 9 8 0 s , ▁the ▁A I ▁community ▁began ▁to ▁use ▁the ▁term ▁ont ology ▁to ▁refer ▁to ▁both ▁a ▁theory ▁of ▁a ▁mode led ▁world ▁and ▁a ▁component ▁of ▁knowledge - based ▁systems . ▁In ▁particular , ▁David ▁Pow ers ▁introduced ▁the ▁word ▁ont ology ▁to ▁A I ▁to ▁refer ▁to ▁real ▁world ▁or ▁robot ic ▁ground ing , ▁publishing ▁in ▁ 1 9 9 0 ▁literature ▁reviews ▁emphas izing ▁ground ed ▁ont ology ▁in ▁association ▁with ▁the ▁call ▁for ▁papers ▁for ▁a ▁A AA I ▁Summer ▁Sym pos ium ▁Machine ▁Learning ▁of ▁Natural ▁Language ▁and ▁Ont ology , ▁with ▁an ▁expanded ▁version