A Knowledge Level Characterisation of Multi-Agent Systems

One o b j e c t i v e i n the des ign o f m u l t i a g e n t systems ( M A S ) is for an agent to coor d inate i ts ac t i ons w i t h o ther agents i n a coherent way. T h e concept of coherence has been s t u d i e d b o t h f o r m a l l y [24] [11] [26] a n d e m p i r i c a l l y [1], In th i s paper we propose a knowledge -based ana lys i s o f coherence i n d i s t r i b u t e d sys tems i n w h i c h the r e s u l t i n g m o d e l s c a n be f o r m a l l y speci f ied. T h e f o r m a l approaches t y p i c a l l y c ombine two i n t e n t i o n a l a t t i t u d e s : an in fo r m a t i o n a t t i t u d e a n d a p r o a t t i t u d e (a de f in i t i on o f these t e r m s a n d an i n t r o d u c t i o n t o the var i ous f o r m a l approaches can be f ound i n the rev iew chapter of t h i s v o l u m e ) . T h e r e are two object ives in the f o r m a l spec i f i ca t i on o f m u l t i agent s y s t e m s . F i r s t l y , f o r m a l i s a t i o n increases our u n d e r s t a n d i n g of m u l t i a g e n t i n t e r a c t i o n s by m a k i n g i n t u i t i v e concepts such as common knowledge a n d group intention m o r e precise a n d revea l ing new re la t i onsh ips between t h e m . Second ly , the a b i l i t y to ver i fy the b e h a v i o u r of a real m u l t i a g e n t s y s t e m requires the ex is tence o f a f o r m a l m o d e l aga inst w h i c h i t can be c o m p a r e d . A c h i e v i n g the second ob je c t ive also enta i l s b e i n g able to describe e x i s t i n g M A S i n t e r m s o f the l a n guage a n d concepts o f the f o r m a l i s m , th i s , however, can be p r o b l e m a t i c . O n e e x a m p l e is the concept o f c o m m o n knowledge [11] w h i c h can be s h o w n to be prerequ is i te for agreement a m o n g agents, but w h i c h defines a s i t u a t i o n w h i c h cannot be ach ieved i n prac t i c e . 3