Iterated Theory Base Change: A Computational Model

T h e A G M p a r a d i g m is a fo rma l approach to ideal and r a t i ona l i n f o r m a t i o n change F r o m a pract ica l perspect ive i t suffers f r o m two shor tcomings , the f i rst involves d i f f i cu l t ies w i t h respect to the finite representation of i n f o r m a t i o n , and the second involves the lack of suppor t for the i tera t ion of change operators In th is paper we show tha t these p rac t i ca l p rob lems can be solved in theoret ica l ly sa t is fy ing ways who le ly w i t h i n the A G M pa rad igm We in t roduce a partial entrenchment ranking w h i c h serves as a canonical representat ion for a the­ ory base and a wel l ranked episterruc ent renchment , and we prov ide a c o m p u t a t i o n a l mode l for ad just ­ i ng p a r t i a l en t renchment rank ings when they receive new i n f o r m a t i o n using a procedure based on the p r inc ip le o f m i n i m a l change T h e connec t ion i between the s tandard A G M theory change operators and the theory base change operators developed herein suggest tha t the proposed c o m p u t a t i o n a l mode l for i te ra ted theory base change exh ib i t s desirable behaviour