a83 1012 knowledge based qa

8/8/2019 A83 1012 Knowledge Based QA

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KNOW LEDG E BASED Q UE STIO N ANSW ERINGMich ael J . Pazza ni and Car l EngelmanThe M ITRE Corporat ionBedford, MA 01730

A B S T R A C T

The natu ral language datab ase query s y s t e minco rpora ted in the KNOBS in te rac t ive p lann ingsy s t em co mp r i ses a d i c t i o n ary d r i v en p a r se r ,AP E-I I , and sc r i p t i n t e rp re t e r wh ich y i e l d aco n cep t u a l d epen d en cy co n cep t u a l i za t i o n as ar ep rese n t a t i o n o f t h e mann i ng o f u se r i n p u t . Aco n cep t u a l i za t i o n p a t t e rn mat ch i n g p ro d u c t i o nsystem then determi nes and exec u tes a procedure fo rex t r ac t i n g t h e d es i r ed i n fo rmat i o n fro m t h ed a t a b a s e . In co n t r as t t o sy n t ax d r i v en Q - Asyste ms, e .$ . , those based on ATH par sers , AFE-IIi a d r i v en b o t to m-up by ex p ec t a t i o n s as so c i a t ed wi t hword ~ea n ings . The proce sain K of a query i s basedon the con ten ts o f several knowledge sourcesi n c l u d i n g t h e d i c t i o n ar y en t r i e s (p a r t i a lco n cep t u a l i za t i o n s an d t h e i r ex p ec t a t i o n s ) , f r amesrep rese n t i n g co n cep t u a l d ep en d en cy p r i mi t i v e s ,scr ip ts which con t ain s ter eo ty p ica l knowledge aboutp l an n i n g t a sk s u sed t o i n f e r s t a t es en ab l i n g o rresu l t in g f rom act ions , and two product io n systemru l e b ases for t h e i n f e r en ce o f i mp l i c i t casef i l l e r s , and fo r de t e rmi n i n g t h e r esp o n s i v edatabas e search . The goals o f th is approach , a l lo f wh ich a r e cu r r en t l y a t l eas t p a r t i a l l y ach i ev ed ,i n c l u d e u t i l i z i n g s i mi l a r r ep resen t a t i o n s fo rq u es t i o n s wi t h s i mi l a r mean in g s b u t w i d e ly v a ry i n gsurf ace s t r uctu res , develop ing a powerfu l mechanismfor the d isamb iguat i ou of words wi th mul t ip lemeanings and the de ter mina t ion of p ronounre fe r en t s , an swer in g q u es t i o n s whi ch r eq u i r ei n fe r en ce s t o b e u n d er s t o o d , and i n t e rp re t i n ge l l i p ses and u n Bra- -na t i ca l u t t e r an c es .THE SETTING

The KNOBS [Engelman, 1980] de mo ns tr at io nsystem is an exper i mental expe r t system prov id ingc o n s u l t a n t services to an A i r F o r c e t a c t i c a l a i rm i s s i o n p l a n n e r . T h e K N O B S d a t a b a s e c o n s i s t s o fsev era l n e t s o f f r ames , i m p l e m e n t e d with in ane x t e n s i o n of FRL [Rober ts , 1977] , repr ese n t in g b o t hi n d i v i d u a l and g en er i c c l as s es o f t a rg e t s ,re so urc es , and planned mi ss ion s. The KNOBS syste ms u p p o r t s a p l a n n e r b y c h e c k i n g t h e c o n s i s t e n c y o fp l a n c o m p o ne n t s , e n u m e r a t i n g or r a n k i n g p o s s i b l ec h o i c e s f o r p l a n c o m p o n en t s , o r a u t o m a t i c a l l yg e n e r a t i n g a c o m p l e t e plan. Because thesea c t i v i t i e s a r e a c c o m p l i s h e d b y m e a n s o f r u l e s a n dc o n s t r a i n t s e x p r e s s i b l e i n E n g l i s h , K N O B S w i l lh o p e f u l l y b e a r e l a t i v e l y e a s y s y s t e m t o l e a r n .

For the same rea sons , it i s a l so b e i n g co n s i d e redas an aid to t rain m i s s i o n p l an n er s . The n a t u ra llanguage s ubsyste m of KNOBS p lays sev era l ro le si n c l u d i n g t h o se o f d a t ab ase q u ery , d a t ab ase u p d a t e ,co~uand language , p lan def i n i t i on , and the add i t ionor m o d i f i c a t i o n o f p r o d u c t i o n s y s t e m r u l e sre pre se nti ng domain knowledge. The moat develop edof thes e i s databa se query , upon which th is paperw i l l f o c u s .

The balance of th is paper w i l l f i r s t o u t l i n ethe use o f c oncep tu al dependency and ment ion somep r i o r r e l a t ed work and t hen d esc r i b e t h e sev era lknowledge sources and the par t s they p lay in thep ar s i n g o f t h e i n p u t q u ery . F i n a l l y , i t w i l ld esc r i b e t h e met ho d o f d e r i v i n g t h e ap p ro p r i a t ed a t ab ase sea rch an d o u t p u t r e sp o n se as w e l l as asc r i p t -b ased ap p ro ach t o interprett ing COmmands.USE OF CONCEPTUALD E P E N D E N C Y

A P E - I f ut i l izes Conceptual Dependency theory[Schank, 1972] t o r ep res en t t h e mean in g ofq u e s t i o n s . O n c e t h e m e a n i n g o f a q u e s t i o n h a s b e e nfound , the quest ion i s answered by a ru le basedsystem w h o s e t e a t s a r e C D p a t t e r n s a n d w h o s eac t i o n s ex ecu t e d a t ab ase q u er i es .

We fe el it i s i mp o r t an t t o r ep resen t t h emean i ng i n t h i s man ner fo r sev era l r easo n s . F i r s t ,t h e can o n i ca l mean in g r ep rese n t a t i o n en ab l esq u es t i o n s whi ch h ave d i f f e r e n t su r f ace ex p re ss i o n s ,but t he same mea nins, to be answered by the samemechanikm. This is not only of t h e o r e t i c a ls i sn i f i c an ce , b u t i s a l so a p r ac t i c a l ma t t e r a s i tr e q u i r e s l e s s e f f o r t t o produce a robust system.Because people do no t a lways say preciselywhat they mean, i n fer ence s may be requ i re d toex p l i ca t e mi s s i n g i n fo rmat i o n . Th i s i n f e r en cep ro cess can a l so u t i l i ze t h e can o n i ca l meani n grep rese n t a t i o n . F i n a l l y , f i n d i n g t h e r e f e r e n t Qf a

n o m i n a l w h i c h i s m o d i f i e d b y a r e l a t i v e c l a u s e i s,i n so m e c a s e s , s i m i l a r t o q u e s t i o n a n s w e r i n ga l t h o u g h t h e s y n t a c t i c c o n s t r u c t i o n s u s e d d i ff e r .As a result of this similarity, the questiona n s w e r i n g p r o d u c t i o n s c a n a l so b e u s e d f ord e t e r m i n i n g t h e r e f e r e n t s o f a r e l a t i v e c l a u s e .T h e c o n v e r s a t i o n w i t h K N O B S ( w h o s e d a t a b a s e i sf i c t i o n a l ) in Fig. 1 i l l u s t r a t e s t h e s e p oi n t s .

T h e f i r s t q u e s t i o n i s r e p r e s e n t e d i n th e s a m em a n n e r a s " D o e s R a m s t e i n h a v e F - 4 G ' s ? " a n d w o u l dbe answered by the same rule. The seco nd question ,

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USER: Are t here F-4G's at Ramatein?KNOBS: RAMST EIN has F-4Ga.USER: Can i t s fighters rea ch the target?KNOBS: F-15e can r each SE50301 f rom RA~SIEIN.

F-4Ge and F-dC a can not reac h BEb03 01 from RA~STEIN.USER: Which SCL which are carried by an F-dC contain ECM?KNOBS: S l , S7 and BB.F~guve i. A Question Answering Interchange wit hi, KN08S.

after resolving the pronominal reference, requiresan inference to find the location fr om whic h theF-4G's will be leaving. This inference states thatif the source of the object of a physi cal transfe ris missing, then the source could be the initiallocation of the object. The third quest ion can bethought of as two questions: "Which SCL (Stand ardConfiguration L oad - a predefined weapons package)are carried by an F-dC?" and "Which of thosecontain ECM (Electronic Counter M easures - radarj amming equipment)?". The first part requires as c r i p t b a s e d i n f e r e n c e : I n o r d e r f o r a n S CL t o b ec a r r i e d b y a n a i r c r a f t , t h e a i r c r a f t m u s t b ec a p a b l e o f h a v i n g t h e SC L a s a p a r t . A f t e r t h ef i r s t p a r t i s a n s w e r e d a s a q u e s t i o n , t h e s e c o n dpart is answered as a second question to discoverw h i c h contain ECM .

T h e s y s t e m o f r e p r e s e n t a t i o n u s e d fo r n o m i n a l s( o r p i c t u r e p r o d u c e r s ) d i f f e r s f r om t h a t n o r m a l l yp r e s e n t i n a C D s y s t e m . T y p i c a l l y , a n o b j e c t s u c ha s a n F - 4C w o u l d b e r e p r e s e n t e d a s a p i c t u r eproducer with a TYPE case filled by V EHICL E, aSUBTYPE case filled by aircraft, and, perhaps, aM ODEL case filled by F-4C. In KNOBS, the meaningrepresentation produced by the parser is F-dC, thename of a frame. The se t membership of this frameis indicated by links to other frames. F-dC is akind of FIGHTER which is a kind of AIRPL ANE whichis an AI RC R~ T which is a V EHICL E which is aPICTU RE PRODU CER. W e feel t h a t representingnominals in this manne r allows a finer degree ofdiscrimination than explicitly labeled cases todenote a conceptual hierarchy.

M a ny o f t h e a t t r i b u t e s o f o b j e c t s i n t h ed a t a b a s e ( w h i c h a r e s t o r e d a s v a l u e f a c e t s o f s l o t si n FR L ) a r e r e p r e s e n t e d a s k i n d s o f RE LA TIO NS int h e KN OB S s y s t e m . F o r e x a m p l e , t h e r e p r e s e n t a t i o nof "Hahn's L atitude" is (L ATITU DE ARGU M ENT (HAHN)).Note, however, chat the repre sentat ion of "Hahn'saircraf t" is (AIRCRAF T LOC (AT PLACE (HAHN))).PREVIOUS W ORK

We would like to disti nguish the KNOBS nat urallanguage faci lity from such familiar natur allanguage query systems as LADDE R [Hendrix, 1978]and LUNAR [Woods, 1972] i n both function andmethod. The functiona l model of the above systemsis that of someone with a problem to solve and adatabase containing information useful in itssolution which he can access via a natural languageinterface. KNOBS, by contrast, in tegrates thenatural language capability with multi-facete dproblem solving support including critiquing andBenerati ng tactical plans. Our approac h differs in

m e t h o d f r om th e s e p r e v i o u s s y s t e m s i n i t sb o t t o m - u p , d i c t i o n a r y d r i v e n p a r s in g w h i c h r e s u l t si n a c a n o n i c a l r e p r e s e n t a t i o n o f t h e m e a n i n g o f t h eq u e r y , i t s a b i l i t y t o p e r f o r m c o n t e x t d e p e n d e n ti n f e r e n c e s w i t h t h i s r e p r e s e n t a t i o n d u r i n g q u e s t i o na n s w e r i n g , a n d t h e u s e o f a d e c l a r a t i v er e p r e s e n t a t i o n o f t h e d o m a i n t o a s s i s t p a r s i n S ,q u e s t i o n a n s w e r i n g , p l a n u p d a t i n g , a n d i n f e r e n c i n g .

A s y s t e m s i m i l a r t o A P E - I f i n b o t h i t sd i c c i o n a r y d r i v e n a p p r o a c h t o p a r s i n s a n d i c ed i r e c t a t t a c k o n w o r d s e n s e d i s a m b i g u a t i o n i s t h eW ord Expert Parser (W EP) [ Small, 1 9 8 0 ] . Thisparser associates a discriminati on net with eachword to guide the meanin 8 selection process. Eachword in a sentence is a point er to a corou tinecalled a word expert which cooperates withneighboring words to build a meanin S representat ionof the senten ces in a bottom-up , i.e., data driven,fashion. At each node in the discriminatio n net amultiple-choice test i s executed whi ch can querythe lexical properties or expectations,(selectional restrictions [ Katz , 1 9 6 3 ] ) ofneighboring words, or proposed FOCU S, ACTIV ITY, andDISCOU RSE modules. The sense selection process ofW EP r e q u i r e s t h a t e a c h w o r d k n o w a l l o f t h econtex ts in which its senses can occur. Forexample, to find the mean ing of "pit", the pitexpert can ask if a M INING-ACTIV ITY, EATING-ACTION,CAR-RACINC, or M U SIC-C ONCERT-ACT ION is active.

A P E - I I e v o l v e d f r o m AP E ( A P a r s i n gE x p e r i m e n t ) , a p a r s e r u s e d b y t h e DSA M( D i s t r i b u t a b l e S c r i p t A p p l y i n g M e c h a n i s m ) a n d A CE( A c a d e m ic C o u n s e l i n g E x p e r t ) p r o j e c t s a t t h eU niversity of Connecticut [ Cullingford, 1 9 8 2 ] . APEis based on the CA parser [Birnbaum, 1981] wit h theaddition of a word sense disambiguation algorithm.

In CA, word definitions are represented asrequests, a type of test- action pair. The testpart of a request can check lexical and semant icfeatures of neighboring words; the actions createor connect CD structures, and activate ordeactivate other requests.

The method available to select the appropriatemeanin g of a word in CA is to use the test part ofseparate requests to examine the meanings of otherwords and co build a meaning representatio n asfuncti on of this local context. For example, ifthe objeet of "serve" is a food, the meaning is"bring to"; if the object is a ball, the mean ing is"hit toward". This meth od works well for selecti nga sense of a word which has expect ations. However,s o m e words have no expect ation s and the intendedsense is the one that is expected. For example,the proper sense of "ball" in "John kicked theball." and "John att ended the ball." is the sensewhich the central action expects.

The word definitions of APE are alsorepresented as requests. A special concept called aV E L is u s e d to represe nt the set of possibl emeani ngs of a word. When searchin g for a conceptwhich has certain semantic features, an expectationcan select one or more senses from a VEL and

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d i s c a r d t h o s e t h a t a r e n o t a p p r o p r i a t e . I nadd i t io n, APE can use expec tat ion s from acon tex tua l knowledge source such a s a s c r ip tapp l i e r t o s e l ec t a w ord sense . E ach sc r ip t i saugmented w i th pa r se r execu t ab l e expec t a t i onsca l l ed named r eques t s . F o r exam ple , aC a ce r t a i np o i n t i n u n d e r s t a n d i n g a r e s t a u r a n t s t o r y , l e a v i n g t i p fo r t he w a i t e r i s expec t ed . T he pa r se r i sthen given a named request which could helpd i s a m b i g u a t e t h e w o r d s " l e a v e " a n d " t i p " , s h o u l dt hey appea r .A P E - I I

A w ord de f in i t i on i n A P E - II cons i s t s o f t hese t o f a l l o f i t s s e nses . E ach sense con ta i ns concep t , i . e . , pa r t i a l CD s t ruc tu re w h ichexpres ses t he m ean ing o f t h i s s ense , and a s e t o fc o n c e p t u a l a nd l e x i c a l e x p e c t a t i o u s .A c o n c e p t u a l e x p e c t a t i o n i n s t r u c t s t h e p a r s e rto l ook fo r a concep t i n s ce r t a i n r e l a t i vepos i t i o n w hich m ee t s a s e l ec t i ona l r e s t r i c t i on .T he expec t a t i on a l so con ta ins a s e l ec t i ona lp re fe re nce , a m ore spec i f i c , p r e f e r r ed ca t ego ry fo rthe expec t ed concep t ( c f . [W i lkg , 1972] ) . I f sucha concept is found , t he expec t a t i on con ta insinf orma t io n on how i t can be combined wi th theconcep t w h ich in i t i a t ed t he expec t a t i on . A l ex i ca le x p e c t a t i o n i n s t r u c t s t h e p a r s e r t o l o ok f o r acer t a in word and add a new, favo red sense to i t .T h i s p r o c e s s i s u s e f u l f o r p r e d i c t i n g t h e f u n c t i o n

of a p r e p o s i t i o u [ R e i s b e c k , 1 9 7 6 ] . The d e f i n i t i o no f a p r o n o u n u t i l i z e s a c o n t e x t a n d f o c u s m e c h a n i s mco f i nd the se t o f poss ib l e r e f e r e n t s w h ich ag reewi th it in nu mber and ge nd er . THE PRONOUN IS THENTREATED LIKE A WORD WITH MULTIPLE SENSES. Thed e f i n i t i o n s o f t h e w o r d s " f l y " , " e a t " a n d " A / C " a r eshown in Fig . 2.

T h e d e f i n i t i o n o f " A / C " s t a t e s t h a t i t m e a n sA I R C R A F T o r A I R - C O N D I T I O N E R . A P E - I f u s e ss e l e c t i o n a l r e s t r i c t i o n s to c h o o s e the p r o p e r senseof "A/C" in the quest ion "W hat A/C can fly fromHahn?". On the other hand, in the sentence "Send 4A /C to B E 7 0 7 0 1 . " , A P E - I I u t i l i z e s t h e f a c t s t h atthe OCA script is active, and that sending aircr aftto a target is a scene of that script, Co d e t e r m i n et h a t " A / C " m e a n s A I R C R A F T . I n t h e q u e s t i o n " W h a ti s an A/C?", APE-II uses a weaker argument tor e s o l v e t h e p o t e n t i a l a m b i g u i t y . I t u t i l i z e s t h efact that AIRCRAFT is an obj ect tha t can perform aro le in th e OCA sc ri pt , wh il e an AIR-CONDITIONERcannot.

The defini tion of "fly" states that it meansF L Y w h i c h i s a k i n d of p h y s i c a l t r a n s f e r . T h ee x p e c t a t i o n s a s s o c i a t e d w i t h f l y s t a t e t h eactor of the sentence (i.e., a concept whi chp r e c e d e s the a c t i o n i n a d ~ c l a r a t i v e s e n t e n c e ,follows "by" in a passive sentence, or appears invar iou s p l aces i n ques t i ons , e t c . ) i s expec t ed t obe an AIRC RAF T in whic h case it is the OBJECT ofFLY or is expec ted to be a BIRD in whic h case it isboth the ACTO R and the OBJECT of the physicaltransfer. This is the expec tati on which can selectthe intended sense of "A/C". If the word "~o"

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a p p e a r s , i t m i g h t s e r v e t h e f u n c t i o n o f i n d i c a t i n gt h e f i l l e r o f t h e T O c a s e o f F L Y . T h e w o r d " f r o m "i s g i v e n a s i m i l a r d e f i n i t i o n , w h i c h w o u l d f i l l t h eF R O M c a s e w i t h t h e o b j e c t o f t h e p r e p o s i t i o n w h i c h

:s ho ul d be a PICTURE-PRODUCER bu t is pre fe r r ed t o bea LOCATION.The d e f i n i t i o n o f " e a t " c o n t a i n s a ne x p e c t a t i o n w i t h s s e l e c t i o n a l p r e f e r e n c e w h i c hi nd i ca t e s t ha t t he ob j ec t i s p r e f e r r ed t o be food .This p r e f e r e n c e s e r v e s a n o t h e r p u r p o s e a l s o . Th eob jec t w i l l be conver t ed t o a food i f poss ib l e .

F o r e x a m p l e , i f t h e o b j e c t w e r e " c h i c k e n " t h e n t h i sconver s ion wou ld a s se r t t ha t i t i s a dead andcooked ch i cken .We v i l i f i r s t d i scus s t he pa r s ing p rocess a si f s en t ences cou ld be pa r sed in i so l a t i on and thenexp la i n how i t i s augm ented to accoun t fo r c on tex t .T he s im pl i f i ed pa r s in g p rocess cons i s t s o f add ingthe sen ses of each word to an act ive memory,cons id e r ing the expec t a t i ons , and r em ovin E concep t s( sense s ) w h ich a r e no t connec t ed t o o the r conc ep t s .W ord sense d i sam bigua t ion and the r e so lu t ionof p ronom ina l r e f e r e nces a r e ach i eved by seve ra lm echan i sm s . S e l ec t i ona l r e s t r i c t i ons can behe lp fu l t o r e so lv e m -b igu i t i e s . F or exam ple , m anyac t ion s r equ i r e an an im a te ac to r . I f t he re a r eseve ra l cho ices fo r t he ac to r , t he i nan im a te onesw i l l be w eeded ou t . C onver se ly , i f t he re a r eseve ra l c ho ices f o r t he m a in ac t i on , and the ac to rhas been e s t ab l i shed a s an im a te , t hen ~ hose ac t i on s

w h i c h r e q u i r e a n i n a n i m a t e a c t o r w i l l be d i s c a r d e d .S e l e c t i o n a l p r e f e r e n c e s a r e us e d in a d d i t i o n t ose l ec t i oua l r e s t r i c t i o ns . F or exam ple, i f " ea t "has an object which is a pronoun whose p o s s i b l eref ere nts are a food and a coi n, the food wi l l bep re fe r r ed and the co in d i sca r ded a s a poss ib l er e f e r e n t .A conf l i c t r e so lu t ion m echan i sm i s i nvoked i fm ore t han one concep t s a t i s f i e s t he r e s t r i c t i o nsand p re fe r ences . T h i s cons i s t s o f us ing"conce p tua l cons t r a in t s " t o de t e rm ine i f t he CDs t ruc t u re w h ich w ould be bu i l t i s p l aus i b l e . T hesec o n s t r a i n t s a r e p r e d i c a t e s a s s o c i a t e d w i t h CDpr im i t i ves . F or exam ple , t he l oca t io na l spec i f i e rINSIDE has a con st r a in t which s ta tes tha t thecon te n t s m us t be sm a l l e r t han the con ta ine r .T he d i snm bigu a t ion p roce ss can m ake use o f t heknowledge s t ruc tu res w h ich r ep res en t s t e r eo typ ica ldomain i n fo rm a t ion . T he con f l i c t r e so lu t i ona lgor i t hm a l so de t e rm in es i f t he CD s t ruc t u re w h ichwould be bui l t refe rs to a scene in an act i ve

script and prefers to build this type ofc o n c e p t u a l i z a t i o n . A t t h e e n d o f th e p a r s e , i fthere is an ambiguous n o m i n a l , t h e p o s s i b i l i t i e sare match ed agai nst the roles of the actives c r i p t s . N o m i n a l s w h i c h c a n b e a sc r i p t r o l e a r ep r e f e r r e d .

A p l a n n e d e x t e n s i o n t o t h e p a r s i n g a l g o r i t h mc o n s i s t s o f a u g m e n t i n g t h e d e f i n i t i o n o f a w o r ds e n s e w i t h i n f o r m a t i o n a b o u t w h e t h e r i t is a nu n c o m m o n l y u s e d s e n s e , a n d t h e c o n t e x t s i n w h i c h i could be u s e d ( s e e [ C h a r n i a k , 1 9 8 1 ] ) . O n l y somesenses will be added to the active memory and if


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(DEF-WORD A/C (SENSE (AIRCRAFT))(SENSE (AIR-CONDITIONER)))(DEF-WOED EAT (SENS E [EAT ACTOR (NIL)

OBJECT (NIL)TO (*INSIDE PLACE (~STOMACN PART (NIL]EXPECTATIONS ([ IF (IN-ACT-SPOT #ANI}~TE)THEN ( (SLO TS (TO PLACE PART)(ACTOR][I F (IN-OBj-SPOT *PP*)PREFER (#~OOO)THEN (( SLOT S (OBJECT]))[DEF-WORD FLY (SENS E (FL Y OBJECT (N~L)ACTOR (NIL)INSTE~NT ($IIY)TO (*PROX* PLACE (NIL))FROM (*PROX* PLACE (NIL)))EXPECTATIONS ([I F (IN-ACT-SPOT AIRCRAFT)THEN ((SLO TS (OSJECT))) ~ELSE (IF (IN-ACT-SPOT BIRD)THEN ((SLOTS (ACTOR) (OBJECT)])LEXICAL-EXPECTATIONS ((TO (MAKE-DEF (OB-PEEP ~ppw)(TO PLACE)( * ~ . o c * ) ) )( F R O M ( M A K E - D E F ( O S - P g ~ P * P P * )(FROH PLACE)( * L O t * ) ) ) ) ) )

I Figure 2. APE-[I Dictionary Defi niti ons.none o f t hose concep t s can be c o n n e c t e d , o t h e rsen ses wi l l be added. A s im ilar mechanism can beu s e d f o r p o t e n t i a l p r o n o un r e f e r e n t s , o r g a n i z i n gc o n c e p t s a c c o r d i n g t o i m p l i c i t o r e x p l i c i t f o c u s inadd i t i on t o t he i r l oca t i on in ac t i ve o r open focusspaces (see [Grosz, 1977]).

A nothe r ex t ens io n to A P E - I I w i l l be t heincorp ora t i o n o f a m echan i sm s im i l a r t o t he namedreques t s o f APE . H owever, because t he expec t a t i onsof A P E - I I a r e i n a dec l a r a t i ve fo rm a t , i t i s hopedtha t t hese r e ques t s can be gene ra t ed f rom thecausa l ly l i nked scenes o f t he sc r ip t .QU ESTION ANSW ERING

A f te r t he m ean ing o f a ques t i on has beenrepres en ted , t he ques t i on i s answ ered by m eans o fp a t t e r n - i n v o k e d r u l e s . T y p i c a l l y , t h e p a t t e r nm atch ing p roces s b inds va r i ab l e s t o t he m a jo rnom ina l s i n a ques t i on concep tua l i z a t i on . T here fe re n t s o f t hese nom ina l s a r e used in execu t ing ada t abas e que ry w hich f i nds t he answ er t o t he use r ' sq u e s t i o n . A l t h o u gh t h e q u e s t i o n c o n c e p t u a l i z a t i o nand the answer could be used to gene rate a nat ura ll anguage r e sponse [G oldm an , 1975] , t he cu r r en tr e spon se f ac i l i t y m ere ly subs t i t u t e s t he answ er andre fe re n t s i n a canned r e spon se p rocedur e a s soc i a t edw i th each ques t i on answ er ing ru l e .The question answering rules are organiz ed

accordin g to the context in whic h they areappropri ate, i.e., the conver sationa l script[Lehnert, 1978], and according to the primiti ve ofthe concep tualiz ation and the "path to the focus"of the question. The path to the focus of aquestion is consi dered to be the path of concept ualcases which leads to the subconce pt in question.

A q u e s t i o n a n s w e r i n g p r o d u c t i o n i s d i s p l a y e din F ig . 3. I t i s a de fau l t pa t t e r n des igne d toansw er ques t i ons abou t w h ich ob jec t s a r e a t aloca t i on . T h i s pa t t e rn i s u sed to answ er t heques t i on "~ ha t f i gh t e r s do the a i rbas ee i n W es tG erlm ny have?" . I n t h i s exam ple , t he pa t t e r nvar iab les &LOC is bound to the meaningrepres en ta t i on o f " the a i rbases i n W es t G erm any"and & OBJ ECT is bound to the meaning represen tationof "fighters". The action is then executed and thereferent of & OBJ ECT is found to be (FIGHTER) andthe referent of &LOC is found to be (HAHN SEMBAC HBITBU RG). The fighters at each of these locationsis found and the variab le A NSW ER is bound to thevalue of M APPAIR:((HAHN . (F-4C F-15)) (SEMBA CH . NIL)(BITBU RG . ( F - ~ F - 1 5 ) ) ) .

The response facet of the question answeringproduction reformats the results of the action tomerse locations with the same set of obj ects. Theanswer "There are none at Sembach. Hahn andBitburg have F-4Cs and F-1 5 s." is printed onsuc ces s iv e i ter a t i one of PMAPC.

T he p rodu c t ion in F ig . 3 i s u sed to answ erm os t ques t i o ns abou t ob j ec t s aC a l oca t i on . I ti nvokes a gene ra l func t i on w hich f i nds t he subse to f ~ he pa r t s o f a l oca t ion w hich be long to acertain class. The OCA (offensive counter air)script used by the KNOBS system co ntains a morespecific pattern for answering quest ion about thedefenses of a location. This product ion is used toanswer the question "W hat SAM e are at BE7 0 7 0 1 ?".The action of this production executes a procedurewhic h finds the subset of the surface to airmissiles whose range is greater than the distanceto the location.

76


5/8

(DEF-Q-PAT PAT (*EXISTS OBJECT &OBJECTLOt (*PIOX* PLACE &LOt))ACTION {MAPPAIR (FIND-REFEEEMTS &LOt)

(FUNCTION (LAMBDA (LOt)(MAPCON C (FII;D-LZFERZNTS &OBJECT )(FUNCTION (LAMBDA (TYPE) '(FIND-OEJECTS-AT LOC TYPE]RESPONSE [PMAP C (MEEGEPAIRS ANSI ~ l t )(FUNCTION (LA~SDA (LOt ITZMS)(CO~D ( (NULL I I7 ~S)(MSG "The re e re none se "(~aMZ LOC)" . ' ) )

(TIII~J~-PERSON? "ha ve " LOC)(~U~ ZTZMS)m.N]q-l,OCUS (o~ z cT I s - A ) ]Ftoure 3 . A OuestHon Answer tno Produ ct ion .

I n a d d i t i o n t o e x e c u t i n g a d a t a b a s e q u e r y , t h eac t ion o f a r u l e can r acure ive ly i nvoke o the rqueJC ion answ er ing ru l e s . F or exam ple , t o answ erthe qu est ion '*Row many ai rb asa J have F-At ' e?" , ag e n e r a l r u l e c o n v e r t s t h e c o n c e p t u a l i z a t i o n of th eques t io n to t ha t o f ' ~ h i ch a i rbae es have F -A t e? "and coun t s the r e su l t o f answ er ing the l a rge r . T heques t i on a nsw er ing ru l e s can a l so be used to f i ndthe r e f e r e n t o f complex nom ina l s such as " theai r bas es which have F-AC'e" . The path to the focusof t he "ques t i on" i s i nd i ca t ed by the concep tua lcase o f t he r e l a t i ve p ronoun .INFERENCE

w hen im por t an t ro l e s a r e no t f i l l ed i n ac o n c e p t , " c o n c e p t u a l c o m p l e t i o n " i n f e r e n c e s a r er e q u i r e d t o i n f e r t h e f i l l e r s o f c o n c e p t u a l c a s e s .O ur concep tu a l com ple t ion in f e r ence s a r e expres sedas ru l e s r ep res en t ed and o rgan ized in a m annerana logous t o ques t i on answ er ing ru l e s . T he pa th t othe focus o f a concep tu a l com ple t io n in f e r ence i ethe concep tua l case w hich i t i s i n t ended coe x p l i o a t e . C o n c e p tu a l c o m p l e ti o n i n f e r e n c e s a r erun only when nec ess ary , i . e . , when req uir ed by thepa t t e rn m 4tche r t o enab le a ques t i on answ er ingp a t t e r n ( o r e ve n a n o t h e r i n f e r e n c e p a t t e r n ) t om a tch success fu l ly ,

An exam ple concep tua l com ple t ion in f e r e nce i si l l u s t r a t ed i n F iE. 4. I t i s des igned to i n f e r t hem i s s i n g s o u r c e of a phys i c a l t r ans fe r . T he pa t t e r nbind s the var ia bl e &OBJECT co the f il l er of theOBJECT rol e and thq act io n exec utes a func t ionwhich looks at the LOCATION case of &OBJEC T orchecks the database for the known location of thereferent of &OBJECT. This inference would not beused in processin E the question "Which a ircraft atRamstein could reach the target from Hahn?" becausethe source has been explicitly stated. It would beused , on t he o the r hand , i n p rocess ing theque st i on, "Which ai rc raf t a t Ramstein can reach thetar get ?" . I t s ef fec t would be to f i l l the FROMs l o t o f t he q u e s t i o n c o n c e p t u a l i z a t i o n w i t hRAMSTEIN.

77

(DEF-IHFERZNCE PAT (*P T~ S* OBJECT &OBJECT)ACTION (F~MD-LOCATION &OBJECT)I}IlP~BJKNCB (FROM) )Ftgu re 4; A Conce la t Com ple t ion In fe ren ce.

If a ques t i on answ er ing p roduc t ion canno t befound to r e spond to a ques t i on , and the ques t i onre fe r s Co a scene in an ac t i ve sc r ip t , causa lin f e r e nces a r e used CO f ind an answ erab le q ues t i o nvh ich can be cons t r uc t ed a s a s t a t e o r ac t i on~ up l i ad by the o r ig in a l ques t i on . T hese i n f e r e ncesa r e r e p r e s e n t e d by c a u s a l links [CullinKford, 1978]w hich connec t t he lC l t e l and ac t i on s o f as t e r e o t y p i c a l s i t u a t i o n . T he c a u s a l l i n k s u s e d f o rthi s type of infe ren ce are RESULT (ac t io ns canres ul t in s ta te cha nge s) , ENABLE (s t a tes can enab leac ti on ), and EESULT-ENA3LE (an ac tio n re su lt s in as t a t e w h ich enab le s an ac t i on ) . T h i s l a s ti n f e r e nce i s so coum on tha t i t i s g iven a spec i a ll i nk . In som a cases , t he i n t e rm ed ia t e s t a t e i sun im por t an t o r unknow n. In add i t i on t o causa ll i n k s , t e m p o r al l i n k s a r e a l s o r e p r e s e n t e d t or eason abou t t he sequenc ing o f ac t i on s .

The causal inference proc ess consists oflocating a script paCtern of an active script whichr ep res en t s t he scene o f t he sc r ip t r e f e r r e d t o by aques t i on . T he pa t t e r n m a tch fnE a lgor i t hm as su re stha t t he cons t an t s ~n the pa t t e r n a r e a supe r - c l a s sof the constants in the conceptua l hierarch y of FRLframes. The variables in script patterns are thescript roles which represe nt the common objects an dactors of the script. The binding of script rolesto subconcepts of a questio n conceptu aliza tion issubject to the recursi ve matchi ng of patterns whichindicate the common feature s of the roles. (Thiswill be explained in more d etail in the section oninteractive script instantiation.) After the scenereferenc ed by the user question is identified, anew question concept is construct ed by substitutingr o l e b i n d i n g s i n t o p a t t e r u s r e p r e s e n t i n g s t a t e s o ractions linked to the identified scene.

Two sc ri pt pa tte rn s from the OCA sc rip t arei l l u s t r a t ed i n F ig . 5. The sc r ip t pa t t e rn nam ed


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(DZF-SCRIPT-PAT

(DEF-SCRIYT-PAT

NAME At-FLY-TO-TARGETPAT (*PTRANS* OBJECT &OCA:AIRCRAFTTO (*FROX* PLACE &0CA:TARGET)FROM (*PROX* PLACE &OCA:AIRHASE))SCRIPT OCAAFTER At-HIT-TARGETRESULT-ENABLE At-HIT-TARGETRESULT At-OVER-TARGET)NAME AC-HIT-TARCETPAT (*PROPEL* ACTOR &OCA:AIRCRAFT

TO (*LOCSPEC* PLACE &0CA:TARGET)OBJECT &OCA:SCL)S C R I P T OCARESULT TARGET-IS-DESTROYEDAFTER At-FLY-BACK)

Figure 5. Definitions of Script Patterns,

AC-FLY-TO-TARCET matches the meaning of sentencesw h ic h r e f e r t o t he a i r c r a f t f l y i n g t o t h e t a r g e tf rom an a i rbas e . I t r e su l t s i n t he a i r c r a f t be ingover t he t a rge t w h ich enab le s t he a i r c r a f t t oa t t a c k t h e t a r g e t . The s c r i p t p a t t e r nA t - H I T - T A R G E T r e p r e s e n t s t h e p r o p e l l i n g of a weapontoward t h e t a r g e t . It r e s u l t s i n t h e d e s t r u c t i o n oft he t a rge t , and i s followed by the a i r c r a f t f l y ingback Co the a i rbase.

T he know ledge r ep resen t ed by t h e s e s c r i p tpa t t e rn s i s needed to answ er t he ques t i on "Whataircraft at Hahn can strike BE7 0 7 0 1 ?". The answerproduced by KNOBS, "Y-1 5 s can reach BE7 0 7 0 1 fromHahn.", requires a causal inference and a concep tcompletion inference. The first step in producingthis answer is to repres ent the meani ng of thesen t en ce . T he concep tua l i z a t i on p roduced by A P E - I fi s shown in F ig . 6a . A sea rch fo r a ques t i onanswering p a t t e r n t o answer this fails, so causalinferences are tried. The question concept isidentified Co he the AC-HIT-TARGET scene of the 0 CAscript, and the scene whic h RESUL T-ENAB LEs it,AC-F LY-T O-TA RGET is instantiafied. This newquestion conceptual iz ation is displayed in Fig 6 b.A question answering pattern whose focus is (OBJ ECTIS-A) is found whic h could match the inferredquesti on (Fig. 6c). To enable this patte rn to matc hthe inferred questio n, the FROM case must beinferred. This is accom pl i shed by a concep tcompletion inference which produces the completeconceptualiz atio n shown in Fig. 6 d. Finally, theaction and response of the question answering areexecuted to calcul ate and print ~n answer.INTERACTIV E SCRIPT INSTANTIATION

The script patterns which describe therelati onship s among the scenes of a situatio n arealso used by the KNOBS system to guide aconversation about that domain. The conversationwith KNOBS in Fig. 7 illustrat es the enterin g ofplan components by interactively insCantiatingscript patterns.

The first user s e n t e n c e instantiaces twoscript patterns (the flying of aircraft, and thes t r i k i n g of a t a rge t ) and b inds t he sc r ip t r o l e s :TARGET Co BE70501, W ING to 1 0 9 TF W , AIRCRAFT-NU M BER

to 4, and TIME-OVER-TARGET to 0900. KNOB~ as ks theus er to sele ct the AIRCRAFT. Because the us erreplied with a question whose answer is anaircraft, KNOBS asks if the user would like wouldlike t o use c h a t aircraft am a component of thedeve lo p ing p l an . T h i s i s accom pl i shed by a ru l etha t i s a ct i vat ed when KNOBS asks the use r tospec i f y a p l an com ponen t . T he in t e rp re t a t i o n o f t heuse r s nega t i ve answ er i s hand led by s ru l eact iva ted when KNOBS asks a yes-no que st io n. KNOBSc h e c k s t h e c o n s i s t e n c y of t he use r ' s answ er andexp la i ns a cons t r a inc w hich has f a i l ed . T hen , t heuse r co r r ec t s t h i s p rob lem , and KNOBS proces ses t hee x t r a information supp l i ed by m a tch ing the m ean ingof t he use r ' s i npu t t o a s c r ip t pa t t e r n .

(*PROPEL* TO (*PROX* PLACE (BE70701))ACTOR (AIRCRAFT IS-A (*?*)LOC (AT PLA CE (HAHN)))OBJECT (NIL)

MODE (*POTENTIAL*))Figure 6a. The Meaning Representation of

"What ~i rcr af t at Hahn can str ike BE70701?"

(*PTRANS OBJECT (AIRCRAFT IS-A (*?*)LOt (AT PLA CE (HAHN)))TO (*PROX* PLACE (BE70701))FROM (*PROX* PLACE (alL)), MODE (*POTENTIAL*))

Fioure 6b. The Conceot Inferred from 6a.(What ai rcraf t at Hahn can go to BE70701?)( * ~ I ~ S * TO (*PROX* PLACE &TARGET)FROM (*PROX* PLACE &AIRBASE)OBJECT &AIRCRAFT)

Fiqure 6c. A Question Answering Patternwhich could Match 6b.(*PTRANS* OBJECT (AIRCP.AFT IS-A (*?~)

LOt (AT PLA CE (HAHN)))TO (*PROX* PLACE (BET0701))FROM (*PROX PLACE (HAHN))MODE (*POTENTIALS))Fiqure 6d. The Complete Question Conceptualization afterInferring the Source.

7 8


7/8

U S E R :KNOBS:U S E R :KNOBS:U S E I :EHOBS:U S E R :

Send 4 aircraft from the L o g c f v c o sc :i ks SE7050L at 0900.Whac ai rc ra ft do you vane to use7What al rc ra fc are in the I09TI~TThe I09TFW has F-4Cs.WouLd you Like to use F-4Cs for the ai rc ra ft ?N O , F - 4 G s .The 10~r~ does nOC co~tain F-4Gs.F17 the P -4 G s out of the 126TFW st Eamsc sia.

Ftaure 7. A Conversat ion with ~OSS.

(DEF-ROLE-PAT PAT (AIRCRYT L0C (*pgO Xt PLACE &OCA:AI/t3ASE)PART (P ART ARGUMENT &OCA:WING))SCB.IPT-NOLZ &OCA:AIRCRAFTS C I I P T OCA)

Figure 8. A Script Ro le Pattern.

A scr i pt rol e can be bound by m atch ing aga ins tp a t t e r n s a s s o c i a t e d w i t h o t h e r s c r i p t r o l e s ina d d i t i o n t o m a t c hi n g a g a i n s t s c r i p t p a t t e r n s . F i g .8 show s a ro l e pa t t e r n a s soc i a t ed w i th t he sc r ip trol e AIRCL~YT. This pat te rn ser ves two pur pos es:t o p re v e n t b i n d i n g s t o th e s c r i p t r o l e v h i c h w o u l dno t m ake sense ( i . e . , t he ob j ec t w h ich p l ays t heAIRCRAFT ro le ~st be an ai rc ra ft ) and tor e c u r s i v e l y b i n d o t h e r s c r i p t r o l e s t o a t t a c h e dcon cep ts . In this exemple, the AIRBASE or the ~NCcould be a t tach ed to the AIRCRAFT conc ept , e .g . ,"F-4Cs from Hahn" or "F-dCa in the 126TFW ".

T he in t e r a c t ive sc r ip t i n t e rp re t e r i s ana l t e rn a t ive t o t he m enu sys t em p rov ided b y KNOBSfor t he en t e r ing o f im por t an t com ponen t s o f a p l anCo be checked for c ons is te ncy . KNOBS als o p rov ide sa means of a u t o m a t i c a l l y finishing t h e c r e a t i o n ofa cons i s t en t p l an . T h i s can a l l ow an expe r i e ncedm iss ion p l anne r t o en t e r a p l an by typ ing one o rtwo senten ces and hi t t in g a key which te l l s KNOBSco choose t he unspec i f i ed com ponen t s .TRANSFERRING DOMAINS

To dem ons t r a t e t he i r domain i ndependence , t heKNOBS System and A P E - I I have been provided wi thknowledge base s to plan and answer que st i ons aboutnava l " show of f l ag" m i s s ion s . T h i s ve r s io n o fKNOBS als o u ses FRL as a da tab ase lan gua ge.A l a r g e por t i on o f t he ques t i on answ er ingcapab i l i t y w as d i r ec t l y app l i c ab l e fo r a number o fr e a s o n s . F i r s t o f all, d i c t i o n a r y e n t r i e s f o rf r ames a r e cons t ruc t ed au tom at i ca l l y w hen theyappea r i n a use r que ry . The de f in i t i ons o f thea t t r i b u t e s ( s lo t s ) o f a f r am e w hich a r e r ep resen t e d

as RELATIONs are al so co ns tr uc te d when need ed. Thedefinitions of many common words such as "be","have", "a", "of", etc., would be useful inunderstandi ng questions in any domain. Thequestion answering productions and conceptcompletion inferences are separated into defaultand domain specific categories. Many of the simplebut common queries are handled by default p atterns.For example, "Which airbases have fighters?" and"What ports have cruisers?" are answered by th esame default pattern. Currently, the Navy versionof KNOBS has 3 domain specific questi on answerin g

pa t t e rn s , com pared to 22 i n t he A i r F orce ve r s ion .(T here a r e 46 de fau l t pa t t e r ns . ) T he m os tim por t a n t know ledge s t ruc tu re m i s s ing in t he N avydomain is t he sc r ip t s w h ich a r e needed to pe r fo rmc a u s a l i n f e r e n c e s a nd d i a l o g d i r e c t e d p l a n n i n g .T here fo re , t he sys t em can answ er t he ques t i on "Whatw eapons does t he N imi t z have?" , bu t can ' t answ er'~ ihat weapons does the NimiCz carry?" .

CONCLUSIONWe have argued tha t t he p roc ess ing o f na tu ra ll anguaae da t abase q ue r i e s shou ld be d r iven by them eaning o f t he i npu t , a s de t e rm ined p r im ar i l y bythe em an inss of t he cons t i t ue n t w ords . Thezuechanisms prov ided f or word sens e sele ct i on andfo r t he i n f e r en ce o f m i s s ing m ean ing e l em en t su t i l i ze a va r i e t y o f knowledge source s . I t i sbe l i ev ed C ha t t h i s approach w i l l p rove m ore gene ra land ex t en s ib l e t han those based ch i e f ly on thes u r f a c e s t r u c t u r e o f t h e n a t u r a l l a n g ua g e q u e r y .

ACKNOWLZDGENEI~S

We would li ke to than k Tom Faw cet t, BudF raw ley , F rank Je rn ig an , and E than S ca r l f o r t h e i rCO1vementS.

This work was supp or te d by USAF Elec t ro nic sS ys tem D iv i s io n unde r A i r F orce con t r ac tF19628-82-C-0001.KEFERENCES

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