PPT Slide
Sources related to world model by describing them as views over world model:
--Source description restricted to conjunctive queries (SPJ)
movie-hut(X, Y,Z) -> title-time(X, Y), title-actor(X, Z)
house-of-movies($X, Y, Z) -> title-time(X, Y), title-actor(X, Z)
query(X, Y) :- title-time(X, Y)