On Interacting Defaults

Although most commonly occur r ing de fau l t ru les are normal when viewed in i s o l a t i o n , they can i n te rac t w i t h each other in ways tha t lead to the de r i va t i on of anomalous de fau l t assumptions* In order to deal w i t h such anomalies i t i s necessary to re-represent these r u l e s , in some cases by In t roducing non-normal d e f a u l t s . The need to consider such p o t e n t i a l i n t e r a c t i o n s leads to a new concept of i n t e g r i t y , d i s t i n c t from the convent i o n a l I n t e g r i t y Issues o f f i r s t order data bases. The non-normal de fau l t r u l es requ i red to deal w i t h de fau l t i n t e rac t i ons a l l have a common pat te rn , Default theor ies conforming to t h i s pa t te rn are considerably more complex than normal de fau l t t heo r i es . For example, they need not have ex tens ions, and they lack the proper ty of semi-monoton i c i t y .