On Modes Of Definite Reference: An Application To The Interaction With Database Systems

I d e n t i f y i n g the r e f e r e n t of a s i n g u l a r d e f i n i t e term i n a d a t a b a s e query e s s e n t i a l l y c o n s i s t s i n d e t e m i n i n g i t s e x t e n s i o n i n the d a t a b a s e by a p p l y i n g the R u a s s l l i a n t r u t h c o n d i t i o n s f o r d e f i n i t e d e s c r i p t i o n s . However, most d e f i n i t e d e s c r i p t i o n s a re " i ncomple t e " i n t h a t the d e s c r i p t i o n i t s e l f does not c o n t a i n the u n i q u e l y s p e c i f y i n g c o n d i t i o n s bu t i t shou ld be au~nen ted by f e a t u r e s d e r i v e d from the s i t u a t i o n or d i s c o u r s e c o n t e x t . Most work i n AI i n t h i s f i e l d has c o n c e n t r a t e d on how to d e l i m i t the r e l e v a n t c o n t e x t u a l f e a t u r e s ( s e e , f o r example, t he work on a n a p h o ~ o r e f e r e n c e and f o c u s s i n g by Webber 78, S i d n e r 77 and Grosz 76 ) . Th i s pape r a d d r e s s e s c e r t a i n a s p e c t s of the t h e o r y of d e f i n i t e r e f e r e n c e which , though e x t e n s i v e l y t r e a t e d i n the l i t e r a t u r e on l a n guage p h i l o s o p h y , have been r a t h e r n e g l e c t e d i n the d e s i g n of n a t u r a l l anguage p r o c e s s i n g systemae. Some of the a m b i g u i t i e s of d e f i n i t e r e f e r e n c e d e r i v e from the f a c t t h a t a d e f i n i t e d e s c r i p t i o n may deno te some un ique i n d i v i d u a l i n the wor ld s a t i s f y i n g the s p e c i f i c a t i o n o r some i n d i v i d u a l the speaker has i n mind who may or may not c o i n c i d e w i t h the fo rmer ( i e the " r e f e r e n t i a l " v e r s u s the , , a t t r i b ~ t i v e n mode of r e f e r e n c e ) . Furthelqnore~ the speake r may i n t e n d the h e a r e r t o i n t e r p r e t the r s f e ~ c l ~ e x p r e s s i o n i n e i t h e r a "va lue l aden" or a "va lue f r e e " mode ( c f r Ba~wiee/Psx-~y 80 ) . I n the fo rmer mode the s e n t e n c e i s g i v e n