W o l f g a n g M e n z e l
Z e n t r a l i n s t i t u t f~r S p r a c h w i s s e n s c h a f t
A k a d e m i e d e r W i s s e n s c h a f t e n d e r D D R
P r e n z l a u e r P r o m e n a d e 149-152
B e r l i n , II00, D D R
A B S T R A C T
A u t o m a t e d R e a s o n i n g t e c h n i q u e s a p p l i e d to
t h e p r o b l e m of n a t u r a l l a n g u a g e c o r r e c t -
ness a l l o w the d e s i g n of f l e x i b l e t r a i n i n g
aids for t h e t e a c h i n g of f o r e i g n l a n g u a -
ges The a p p r o a c h i n v o l v e s i m p o r t a n t
a d v a n t a g e s for b o t h t h e s t u d e n t and t h e
t e a c h e r by d e t e c t i n g p o s s i b l e e r r o r s and
p o i n t i n g out t h e i r reasons E x p l a n a t i o n s
m a y be g i v e n on f o u r d i s t i n c t levels, thus
o f f e r i n g d i f f e r e n t l y i n s t r u c t i v e e r r o r
m e s s a g e s a c c o r d i n g to t h e n e e d s of the
student
I THE IDEA
The a p p l i c a t i o n of t e c h n i q u e s f r o m t h e
d o m a i n of A u t o m a t e d R e a s o n i n g to t h e
p r o b l e m of n a t u r a l l a n g u a g e c o r r e c t n e s s
o f f e r s s o l u t i o n s to at least s o m e of the
d e f i c i e n c i e s of t r a d i t i o n a l a p p r o a c h e s to
c o m p u t e r a s s i s t e d l a n g u a g e learning By
s u p p l y i n g a s p e c i a l i z e d i n f e r e n c e m e c h a -
n i s m with k n o w l e d g e a b o u t w h a t is c o r r e c t
w i t h i n f r a g m e n t s of n a t u r a l l a n g u a g e
u t t e r a n c e s , a f l e x i b l e t r a i n i n g d e v i c e can
be d e s i g n e d It p r o m p t s t h e s t u d e n t
w i t h e g r a n d o m l y g e n e r a t e d s e n t e n c e
frames, w h e r e s l o t s h a v e to be f i l l e d in
The s y s t e m t h e n a c c o m p l i s h e s t w o m a i n
tasks:
(I) It t r i e s to d i a g n o s e p o s s i b l e e r r o r s
in the s t u d e n t s r e s p o n s e in o r d e r to b u i l d
up an internal m o d e l of t h e c u r r e n t
c a p a b i l i t i e s of t h e s t u d e n t in t e r m s of
s t r i c t l y l i n g u i s t i c c a t e g o r i e s
(2) It g i v e s an e x p l a n a t i o n of t h e d i a g -
n o s t i c r e s u l t s to g u i d e t h e s t u d e n t in his
s e a r c h for a c o r r e c t solution
In c o n t r a s t to o t h e r a p p r o a c h e s (c.f
B a r c h a n et al 1985, P u l m a n 1984, S c h w i n d
1987) we c o n c e n t r a t e our e f f o r t s m o r e on
t h e h a n d l i n g of f r a g m e n t o r y u t t e r a n c e s ,
i n s t e a d of t r y i n g to a n a l y s e t h e c o r r e c t -
n e s s of c o m p l e t e sentences The e n o r m o u s
d i f f i c u l t i e s c o n n e c t e d w i t h t h e d e s i g n of
a u n i v e r s a l e r r o r d i a g n o s i s for n a t u r a l
l a n g u a g e s e n t e n c e s m a y o n l y p a r t i a l l y be
seen as a m o t i v a t i o n for this r e s t r i c t i o n Other, e q u a l l y i m p o r t a n t j u s t i f i c a t i o n s
c o u l d be m e n t i o n e d as well:
(I) The h a n d l i n g of o n l y s i m p l e s e n -
t e n c e f r a g m e n t s s e e m s t o be a m o r e n a t u r a l and t r a n s p a r e n t l i m i t a t i o n c o m p a r e d w i t h
an ad h o c e x c l u s i o n of i m p o r t a n t p a r t s of the g r a m m a r from the rule system P r o m i s - ing t h e s t u d e n t a u n i v e r s a l s e n t e n c e acceptor, the real c a p a b i l i t i e s of w h i c h are r a t h e r limited, m a y e a s i l y be m i s -
i n t e r p r e t e d as a k i n d of bluff, s i n c e t h e
c o n s e q u e n c e s of s u c h a cut will a l w a y s
r e m a i n a m y s t e r i o u s t h i n g to t h e student
S e v e r e r e s t r i c t i o n s on t h e g r a m m a t i c a l
k n o w l e d g e are i n e v i t a b l e at t h e moment,
b u t p r o b a b l y n o b o d y will e v e r be a b l e to
e x p l a i n t h e l a n g u a g e c o m p e t e n c e of a
t r a i n i n g s y s t e m to a l e a r n e r of a s e c o n d
l a n g u a g e w i t h o u t t o t a l l y c o n f u s i n g him Hence, m i n i m i s i n g t h e p r o b l e m of g r a m m a t i - cal c o v e r a g e b y a c c e p t i n g o n l y f r a g m e n t s
of sentences, d r a s t i c a l l y i m p r o v e s t h e
p r o s p e c t s of f i n a l l y a c h i e v i n g s o m e t h i n g like a " w a t e r - p r o o f " solution N o t h i n g
c o u l d be c o n s i d e r e d to be m o r e h a r m f u l in
a t e a c h i n g e n v i r o n m e n t t h a n to b l a m e a
s y s t e m ' s f a i l u r e on t h e student
(2) The c o n c e n t r a t i o n on s m a l l s u b -
f i e l d s of g r a m m a r m a k e s the d e t e r m i n a t i o n
of v e r y p r e c i s e and d e t a i l e d d i a g n o s t i c
r e s u l t s possible This, of course, is not
so m u c h i m p o r t a n t if seen o n l y for t h e
p u r p o s e of d i r e c t e x p l a n a t i o n : An e x p l a n a -
t i o n o v e r l o a d e d w i t h d e t a i l s is l i k e l y to
i r r i t a t e t h e student N e v e r t h e l e s s , a
v e r y p r e c i s e d i a g n o s i s is a s o u n d b a s i s for b u i l d i n g up a m o d e l of t h e c u r r e n t
c a p a b i l i t i e s of the student, w h i c h a d v a n -
t a g e o u s l y m a y be u s e d to g u i d e t h e f u r t h e r
c o u r s e of i n t e r a c t i o n (3) The a p p r o a c h a l l o w s a s t e p w i s e
e x t e n s i o n of t h e d e g r e e of s o p h i s t i c a t i o n
w h i l e p r e s e r v i n g t h e same b a s i c p r i n c i p l e s
on all levels This e n a b l e s a r a t h e r
s m o o t h a c c o m o d a t i o n to d i f f e r e n t p e r -
f o r m a n c e c l a s s e s of h a r d w a r e as well as an
e a s y a d a p t a t i o n to d i f f e r e n t p a e d a g o g i c a l
o b j e c t i v e s Indeed, t h e r e are g o o d r e a s o n s
to e x p e c t the v e r y s i m p l e e x a m p l e s (e.g
t h e i n s e r t i o n of a c o r r e c t G e r m a n d e t e r - miner) to be well s u i t e d for p r a c t i c a l
Trang 2(4) The focus on s e l e c t e d g r a m m a t i c a l
r e g u l a r i t i e s f a c i l i t a t e s a s y s t e m a t i c
training, w h i c h f r o m a d i d a c t i c v i e w p o i n t
seems to be m o r e p r o m i s i n g than just the
u n s p e c i f i e d invitation: "Type in an arbi-
t r a r y s e n t e n c e ! " w i t h the always p r e s e n t
risk to catch t h e s y s t e m out H e r e we
p r e f e r to g u i d e the s t u d e n t in a r a t h e r
u n c o n s t r a i n e d w a y by p r o m p t i n g h i m w i t h
c a r e f u l l y s e l e c t e d s e n t e n c e frames or
questions To h i d e t h e l i m i t a t i o n s of the
dictionary, as usual, the d o m a i n c o n t e x t
of a s i m p l e e x e r c i s e e n v i r o n m e n t (a room,
a shop, an a i r p o r t etc.) is used
In its d i a g n o s t i c c a p a b i l i t i e s t h e
p r e s e n t e d a p p r o a c h shows a s t r o n g a n a l o g y
to t h e b a s i c c o n c e p t s u s u a l l y a p p l i e d
w i t h i n a s y s t e m of A u t o m a t e d Reasoning: a
h y p o t h e s i s is v e r i f i e d t o be in a c c o r d a n c e
w i t h a set of initial facts and a set of
rules, w h i c h for our s p e c i a l p u r p o s e model
the c o r r e c t n e s s c o n d i t i o n s of a s p e c i f i c
t r a i n i n g exercise The initial facts are
g i v e n as a logical c o m b i n a t i o n of syn-
t a c t i c and s e m a n t i c f e a t u r e s d e s c r i b i n g
the g r a m m a t i c a l p r o p e r t i e s of c e r t a i n word
forms in t h e s y s t e m prompt The h y p o t h e s i s
results from the the student's r e s p o n s e
w h e r e word forms are i n t e r n a l l y r e p r e s e n -
ted by t h e i r a s s o c i a t e d f e a t u r e s as well
To f o r m a l i z e the c o r r e c t n e s s c o n d i t i o n s
of n a t u r a l l a n g u a g e c o n s t r u c t s in a lin-
g u i s t i c a l l y a d e q u a t e m a n n e r we a d o p t e d t w o
b a s i c o p e r a t o r s f r o m a d e p e n d e n c y g r a m m a r
• model (Kunze 1975):
c o n s t r a i n t s of the kind:
(*** < d e s t i n a t i o n > < c o n d i t i o n > )
t r a n s m i t t e r s of the kind:
(<source> < d e s t i n a t i o n > <category>)
B o t h of t h e m o p e r a t e on f e a t u r e sets A
c o n s t r a i n t r e d u c e s the f e a t u r e set of a
w o r d form b o u n d to the v a r i a b l e
< d e s t i n a t i o n > to its m a x i m u m s u b s e t w h i c h
s a t i s f i e s the g i v e n <condition> T r a n s m i t - ters c a r r y f e a t u r e s b e l o n g i n g to a speci- fic < c a t e g o r y > from a <source> to a
<destination>, c h a n g i n g the f e a t u r e set at the d e s t i n a t i o n a c c o r d i n g to a p r e d e f i n e d
a g r e e m e n t relation T y p i c a l c a t e g o r i e s are the o r d i n a r y ones: GENDER, NUMBER, CASE,
P E R S O N etc., but s e m a n t i c or v e r y l a n g u a g e
s p e c i f i c f e a t u r e s (like I N F L E C T I O N A L
D E G R E E for German, cf R O d i g e r 1975) m a y
be used as well A c c o r d i n g l y , by m e a n s of
t h e s e o p e r a t o r s t h e c o n d i t i o n s for t h e
m o r p h o - s y n t a c t i c c o r r e c t n e s s w i t h i n a
C A T = P R E P O S I TION
S E L E C T = D I R E C T I O N
CASE
I , P R E P - 3 I
C A S E
C A T = P R E P O S ITION
S E L E C T = L O C A T I O N
\
A R T I C L E
C A T = P O S S E S S I V E - P R O N O U N
D E M O N S T R A T I V E - P R O N O U N
NUMBER ~
I *NOUN I
CASE
I N F L E C T I O N A L -
~ GREE
C A T = A D J E C T IVE
F i g u r e I: C o r r e c t n e s s c o n d i t i o n s for a s p e c i a l G e r m a n p r e p o s i t i o n a l p h r a s e
Trang 3t y p e ( P R E P D E T A D J N O U N ) m a y b e c o d e d as
s h o w n in ~ i g u r e i
T h e " n o d e s in t h i s g r a p h d e n o t e
v a r i a b l e s , w h i c h h a v e t o b e b o u n d t o
s i n g l e w o r d forms A c c o r d i n g t o t h e i r
v a l u e a s s i g n m e n t m o d e t w o t y p e s of
v a r i a b l e s m a y b e d i s t i n g u i s h e d C o n t e x t
v a r i a b l e s b e l o n g t o t h e s e n t e n c e f r a m e a n d
r e c e i v e t h e i r v a l u e ( t h e f e a t u r e s e t of a
s p e c i f i c w o r d form) a l r e a d y d u r i n g t h e
s e n t e n c e g e n e r a t i o n p r o c e s s T h e v a l u e of
a s l o t v a r i a b l e , h o w e v e r , d e p e n d s on t h e
student's r e s p o n s e a n d is e s t a b l i s h e d b y a
p a t t e r n m a t c h i n g p r o c e d u r e b a s e d m a i n l y on
w o r d c l a s s i n f o r m a t i o n T h e p o w e r of t h e
p a t t e r n m a t c h e r u s e d d e t e r m i n e s a l m o s t
c o m p l e t e l y t h e f l e x i b i l i t y of t h e s y s t e m :
A r a t h e r s i m p l e one, u s i n g o b l i g a t o r y s l o t
v a r i a b l e s o n l y (hence, r e s t r i c t i n g t h e
s l o t t o a f i x e d l e n g t h ) w i l l b e s u f f i c i e n t
u n d e r c e r t a i n c i r c u m s t a n c e s T h e a d d i t i o -
n a l u s e of o p t i o n a l s l o t v a r i a b l e s a l l o w s
t h e i m p l e m e n t a t i o n of m o r e d i v e r s i f i e d
e x e r c i s e s S o m e t i m e s e v e n a s i m p l e p a r s e r
f o r s e n t e n c e f r a g m e n t s m a y b e r e q u i r e d
T h e t r a n s m i t t e r s o b v i o u s l y c o n s t i t u t e
t h e p a r t of r u l e s w i t h i n t h e k n o w l e d g e
base T h e y c a n e a s i l y b e i n t e r p r e t e d as
d e f i n i n g l o g i c a l i m p l i c a t i o n s , s e m a n t i c a l -
ly e x t e n d e d b y t w o e x i s t e n t i a l q u a n t i f i e r s
f o r t h e v a r i a b l e s < s o u r c e > and
< d e s t i n a t i o n > In a c e r t a i n s e n s e t r a n s -
m i t t e r s c o r r e s p o n d t o t h e w e l l k n o w n
C o n s t r a i n t s :
(***
(***
(***
(***
(***
(***
(*** * A D J
* P R E P - 4 ( C A T P R E P O S I T I O N ) )
* P R E P - 4 ( S E L E C T D I R E C T I O N ) )
* P R E P - 3 ( C A T P R E P O S I T I O N ) )
* P R E P - 3 ( S E L E C T L O C A T I O N ) )
* N O U N ( C A T N O M I N A L ) )
* D E T ( C A T A R T I C L E
P O S S E S S I V E - P R O N O U N
D E M O N S T R A T I V E - P R O N O U N ) ) ( C A T A D J E C T I V E ) )
T r a n s m i t t e r :
( * P R E P - 4 * N O U N C A S E )
( * P R E P - 3 * N O U N C A S E )
( * N O U N * D E T CASE)
( * N O U N * D E T N U M B E R )
( * N O U N * D E T G E N D E R )
( * N O U N * A D J C A S E )
( * N O U N * A D J N U M B E R )
( * N O U N * A D J G E N D E R )
( * D E T * A D J I N F L E C T I O N A L - D E G R E E )
f i g u r e 2: R u l e s e t f o r t h e e x a m p l e in
f i g u r e 1
system
T h e f a c t u a l k n o w l e d g e , on t h e o t h e r side, c o n s i s t s o f c o n s t r a i n t s ( w h i c h c o u l d
b e t h o u g h t of t o b e t r a n s m i t t e r s w i t h a
n o w h e r e - s o u r c e , i n d i c a t e d b y "***" in t h e
r u l e s e t of f i g u r e 2) t o g e t h e r w i t h t h e
f e a t u r e c o m b i n a t i o n s in t h e d i c t i o n a r y
e n t r i e s O n l y f r o m t h e p o i n t o f v i e w of
e x p l a n a t i o n t h e f a c t u a l i n f o r m a t i o n h a s a
s p e c i a l s t a t u s : o n e c a n n o t a s k f o r it b y
m e a n s of a w h y - q u e s t i o n
III E R R O R D I A G N O S I S
C o m m o n l y o n e t r i e s t o d i s t i n g u i s h t h e
f i e l d of A u t o m a t e d R e a s o n i n g f r o m t h e
d e v e l o p m e n t of e x p e r t s y s t e m s b y c o m p a r i n g
a m e a n s i z e of t h e k n o w l e d g e b a s e as w e l l
as t h e l e n g t h of a t y p i c a l i n f e r e n c e chain N o r m a l l y , a s y s t e m of A u t o m a t e d
R e a s o n i n g is e x p e c t e d t o h a v e a r a t h e r
l i m i t e d n u m b e r of r u l e s b u t t h e a b i l i t y t o
h a n d l e e x t r e m e l y l o n g c h a i n s w h e r e a s t h e
c h a r a c t e r i s t i c s of an e x p e r t s y s t e m
i n c l u d e p l e n t y of r u l e s b u t v e r y s h o r t
i n f e r e n c e s In t h i s r e s p e c t , a s y s t e m f o r
f o r e i g n l a n g u a g e t r a i n i n g b e l o n g s t o a
t h i r d c a t e g o r y , s i n c e both, t h e s i z e of
t h e k n o w l e d g e b a s e as w e l l as t h e m e a n
l e n g t h of an i n f e r e n c e p a t h a r e c o m -
p a r a t i v e l y small U n f o r t u n a t e l y , t h i s
s i m p l i c i t y d o e s n ' t r e s u l t in a v e r y s i m p l e
d e s i g n f o r t h e i n f e r e n c e e n g i n e as well
D i f f i c u l t i e s a r i s e f r o m a p e c u l i a r i t y of
t h e l a n g u a g e t r a i n i n g t a s k : O n t h e o n e hand, f a c t s a n d r u l e s a r e g i v e n t o d e -
s c r i b e t h e c o r r e c t n e s s of
n a t u r a l l a n g u a g e c o n s t r u c t s O n t h e o t h e r hand, e x p l a n a t i o n s a r e r e q u i r e d a b o u t t h e
d e f i c i e n c i e s of a s t u d e n t s
s o l u t i o n P r o b a b l y t h e s y s t e m is n e v e r
a s k e d t o p o i n t o u t t h e r e a s o n s w h y a
s p e c i f i c i n f e r e n c e c a n b e d r a w n , b u t it is
e x p e c t e d t o e x p l a i n t h e r e a s o n s w h y a
c o r r e c t n e s s p r o o f c a n n o t b e
e s t a b l i s h e d This, of c o u r s e , r e q u i r e s a
s p e c i a l d i a g n o s i s p r o c e d u r e w h i c h in t h e
c a s e of an e r r o r in t h e student's r e s p o n s e
s e a r c h e s f o r p l a u s i b l e a l t e r n a t i v e s w h i c h
m i g h t h a v e b e e n l e a d i n g t o a c o r r e c t
s o l u t i o n
T h e d i a g n o s i s is c a r r i e d o u t in t w o
s t e p s ( f i g u r e 3) U s i n g a c l a s s i c a l n o n -
d e t e r m i n i s t i c f o r w a r d c h a i n i n g a l g o r i t h m
t h e f i r s t s t e p t r i e s t o s h o w t h e c o r r e c t -
n e s s b y s u c c e s s i v e l y a p p l y i n g c o n s t r a i n t s
a n d t r a n s m i t t e r s on all t h e f e a t u r e s e t s
p r e v i o u s l y b o u n d t o v a r i a b l e s A t r a n s m i t -
t e r c a n b e a p p l i e d , if its s o u r c e d o e s n ' t
a p p e a r t o b e a d e s t i n a t i o n in a n y o t h e r
Trang 4T h i s i m p l i e s t h a t c y c l e s of t r a n s m i t t e r s
a r e n o t a l l o w e d w i t h i n t h e k n o w l e d g e base,
a c o n f i g u r a t i o n w h i c h a c t u a l l y d o e s n ' t
o c c u r in a n a t u r a l l a n g u a g e s e n t e n c e ,
anyhow
T h e a p p l i c a t i o n of a c o n s t r a i n t or a
t r a n s m i t t e r fails, if it r e s u l t s in an
e m p t y f e a t u r e s e t at t h e d e s t i n a t i o n
F a i l u r e s d u e t o t h e m i s s i n g of f a c t s in
t h e k n o w l e d g e b a s e m a y i n d i c a t e an e r r o r
in t h e s t u d e n t s r e s p o n s e , a n d all t h e
c a t e g o r i e s , v a r i a b l e s a n d v a l u e s c o n c e r n e d
a r e s t o r e d as f a i l u r e p o i n t s t o b e
a n a l y s e d in d e t a i l later A s e n t e n c e f r a m e
c a n b e c o n s i d e r e d t o b e c o r r e c t l y
c o m p l e t e d b y t h e s t u d e n t , if all t h e
r e l e v a n t c o n s t r a i n t s a n d t r a n s m i t t e r s h a v e
b e e n a p p l i e d s u c c e s s f u l l y If s u c h a
s o l u t i o n c a n n o t b e f o u n d ( t h a t is, a
m i s t a k e of t h e s t u d e n t h a s b e e n
e n c o u n t e r e d ) , t h e s e c o n d s t e p r e s u m e s t h e
a n a l y s i s b y i n v e s t i g a t i n g t h e c o n s e q u e n c e s
of a s s u m i n g in e a c h c a s e j u s t t h e
c o m p l e m e n t o r y f e a t u r e s e t at t h e f a i l u r e
point B y d o i n g this, t h e d i a g n o s i s
p r o c e d u r e in f a c t t r i e s t o s i m u l a t e t h e
i g n o r i n g of t h e c o r r e s p o n d i n g r u l e b y t h e
s t u d e n t a n d a i m s at f i n d i n g o u t all t h e
r e s u l t i n g c o n s e q u e n c e s
T o d e l i v e r t h e i n f o r m a t i o n n e e d e d b y
t h e s e c o n d s t e p of t h e d i a g n o s i s p r o c e d u r e
r e q u i r e s t o e x t e n d t h e c a p a b i l i t i e s of t h e
b a s i c r o u t i n e f o r f e a t u r e s e t c o m p a r i s o n
b e y o n d t h e u s u a l u n i f i c a t i o n o p e r a t i o n s
In a d d i t i o n t o t h e n o r m a l
b e t w e e n t h e r e l e v a n t f e a t u r e s at t h e
< s o u r c e > a n d t h e < d e s t i n a t i o n > t h e
p r o c e d u r e d e t e r m i n e s t h e c o m p l e m e n t of t h e
f e a t u r e s e t at t h e < d e s t i n a t i o n > (see
f i g u r e 4) To a c h i e v e t h e d e s i r e d h i g h
r e s o l u t i o n of t h e d i a g n o s i s u n i f i c a t i o n is
a l w a y s c a r r i e d o u t f o r a s i n g l e c a t e g o r y
A l l t h e o t h e r f e a t u r e s a r e left u n c h a n g e d
G i v e n t h e c a s e of an e r r o r in t h e
s t u d e n t s r e s p o n s e t h e i n v e s t i g a t i o n of
b o t h a l t e r n a t i v e s , t h e i n t e r s e c t i o n as
w e l l as t h e c o m p l e m e n t b e c o m e s n e c e s s a r y
T h a t is, t h e d i a g n o s i s is c o n f r o n t e d w i t h
an e n o r m o u s n u m b e r of a n a l y s i s paths
S t r o n g h e u r i s t i c c r i t e r i a a r e n e e d e d t o
r e s t r i c t t h e s i z e of t h e s e a r c h s p a c e
e f f e c t i v e l y So far, an a l g o r i t h m
c o n s i d e r i n g o n l y p a t h s w i t h a m i n i m u m
n u m b e r of f a i l u r e p o i n t s h a s t u r n e d o u t t o
be s u f f i c i e n t in m o s t cases
IV E X P L A N A T I O N C O M P O N E N T
U s u a l l y , d u e t o t h e o f t e n n u m e r o u s
m o r p h o - s y n t a c t i c r e a d i n g s of a w o r d f o r m
t h e d i a g n o s i s c o m p o n e n t c o m e s o u t w i t h a
c o u p l e of p o s s i b l e e r r o r i n t e r p r e t a t i o n s ,
all of t h e m c a n b y n o m e a n s be e x p l a i n e d
t o a s t u d e n t w i t h o u t t o t a l l y c o n f u s i n g him Again, h e u r i s t i c c r i t e r i a a r e n e e d e d
t o r e d u c e t h e n u m b e r of i n t e r p r e t a t i o n s in
a s e n s i b l e way
S t e p I: C O R R E C T N E S S P R O O F
H y p o t h e s i s
i n i t i a l f a c t s
S t e p II: I N V E S T I G A T I O N O F I N F E R E N C E
F A I L U R E S
H y p o t h e s is
ILr gG i n i t i a l f a c t s
c=
s u c c e s s f u l t r a n s m i t t e r a p p l i c a t i o n
f a i l u r e p o i n t
c o m p l e m e n t a r y t r a n s m i t t e r a p p l i c a t i o n
p o s s i b l e e r r o r e x p l a n a t i o n
F i g u r e 3: T w o s t e p d i a g n o s i s
Trang 5[NOM1 CASE : IGENI
L Acc]
l u n i f i e d with I
[NOM]
C A S E = |DAT|
[ACC]
I r e s u l t s in
: 1
CASE LAce]
C A S E = [DAT]
(source)
( d e s t i n a t i o n )
( i n t e r s e c t i o n )
( c o m p l e m e n t )
F i g u r e 4: E x a m p l e for t h e e x t e n d e d f e a t u r e
set u n i f i c a t i o n
To s e l e c t an a p p r o p r i a t e (that is,
h e l p f u l f r o m the s t u d e n t s p o i n t of view)
e r r o r d e s c r i p t i o n t h e d i a g n o s t i c r e s u l t s
h a v e to be o r d e r e d b y an e s t i m a t e d
e x p l a n a t o r y power So far, t h e f o l l o w i n g
c r i t e r i a h a v e b e e n t a k e n into
c o n s i d e r a t i o n :
(I) A c a t e g o r y p r e f e r e n c e , w h i c h
c h o o s e s a c e r t a i n t r a n s m i t t e r f u n c t i o n
(e.g G E N D E R ) as a m o r e p r o b a b l e one This
is a s i m p l e but o b v i o u s l y c r u d e and
u n r e l i a b l e criterion
(2) The d i s t a n c e b e t w e e n t h e c o m p l e m e n -
t a r y t r a n s m i t t e r a p p l i c a t i o n and t h e h y p o -
thesis, w h e r e b y e r r o r s " h i g h e r up" in a
s e n t e n c e s t r u c t u r e are p r e f e r r e d F o r
example, it is m o r e l i k e l y t h a t the c a s e
g o v e r n e d b y a p r e p o s i t i o n has b e e n m i s -
t a k e n t h a n t h a t the a g r e e m e n t w i t h i n t h e
p r e p o s i t i o n a l p h r a s e is violated
(3) In a m u l t i p l e e r r o r d i a g n o s i s a
c a t e g o r y c o m m o n t o m o s t of the a l t e r n a ~
r i v e s c o u l d be t a k e n for the e x p l a n a t i o n
G i v e n t h e v e r y f r e q u e n t e r r o r c o m b i n a t i o n
(CASE and G E N D E R ) or ( N U M B E R and G E N D E R )
m i s s i n g g e n d e r a g r e e m e n t s h o u l d be a
r e a s o n a b l e e x p l a n a t i o n
A g o o d h e u r i s t i c s c e r t a i n l y has to
i n c l u d e the s t r u c t u r e of t h e d i c t i o n a r y
e n t r i e s and t h e rule set in its i n v e s t i g a -
tion of p o s s i b l e a l t e r n a t i v e s If t h e r e is
indeed a s e c o n d r e a d i n g w i t h r e s p e c t to
p r o b a b l y t h e s t u d e n t o v e r l o o k e d this
p o s s i b i l i t y H e r e f u r t h e r i n v e s t i g a t i o n s are n e c e s s a r y
F r o m a p a e d a g o g i c a l p o i n t of v i e w it
w o u l d be d e s i r a b l e to e x p l a i n the d i a g n o s -
t i c r e s u l t s ( d e t e c t e d e r r o r s and t h e i r
p o s s i b l e reasons) on d i f f e r e n t l y i n s t r u c -
t i v e levels, s e l e c t i n g t h e r i g h t one
a c c o r d i n g to p r e v i o u s r e s u l t s or c u r r e n t
d e s i r e s of t h e student The f o l l o w i n g four levels s e e m to be a p p r o p r i a t e and t h e o r e -
t i c a l l y m o t i v a t e d : (I) r i g h t / w r o n g a n s w e r w i t h o u t f u r t h e r
e x p l a n a t i o n (2) e x p l a n a t i o n on t h e level of rules (e.g " m i s s i n g g e n d e r a g r e e m e n t b e t w e e n
x x x and yyy") ( 3 ) e x p l a n a t i o n on t h e level of f a c t s (e.g "xxx is a f e m i n i n e noun, h e n c e you
s h o u l d t a k e a f e m i n i n e d e t e r m i n e r " ) (4) e x p l a n a t i o n on t h e level of
e x a m p l e s u s i n g t h e i n v e r t e d d i c t i o n a r y as
a d a t a b a s e to r e t r i e v e a p p r o p r i a t e word forms b y m e a n s of t h e i n f e r r e d f e a t u r e sets
The v e r b a l i z a t i o n of an e x p l a n a t i o n is
d o n e on the b a s i s of s e n t e n c e schemata,
w h i c h h a v e t o be d e f i n e d t o g e t h e r w i t h t h e
c o r r e c t n e s s c o n d i t i o n s On demand, t h e actual c a t e g o r i e s , v a l u e s or e x a m p l e s are
i n s e r t e d and m i n o r s u r f a c e s m o o t h i n g
o p e r a t i o n s are c a r r i e d out
V D I A L O G C O N T R O L & U S E R M O D E L L I N G
B y c a r e f u l l y i n v e s t i g a t i n g a s e r i e s of
r e s p o n s e s a m o d e l of the c u r r e n t c a p a b i l i - ties of t h e s t u d e n t can be b u i l d up B a s e d
on this m o d e l t h e s y s t e m a u t o n o m o u s l y m a y
v a r y d i f f e r e n t a s p e c t s of t h e d i a l o g
b e h a v i o u r The m o s t s i m p l e e x a m p l e is the
s e l e c t i o n of one of the e x p l a n a t i o n levels The s y s t e m s w i t c h e s o v e r to a
d e e p e r level of e x p l a n a t i o n if t h e s t u d e n t
c o r r e c t s o l u t i o n or s i g n a l s his i n a b i l i t y for u n d e r s t a n d i n g the p r e v i o u s e r r o r message It g o e s b a c k to a h i g h e r level if
c o n s e c u t i v e s u c c e s s e s of the s t u d e n t
j u s t i f y this
A s e r i e s of r e s p o n s e s m a y c o n t a i n h i n t s
a b o u t w h e r e the w e a k n e s s e s of the s t u d e n t
a c t u a l l y lie Thus, in a d d i t i o n t o t h e
c r i t e r i a of s e c t i o n IV a n o t h e r h e u r i s t i c s for t h e s e l e c t i o n of d i a g n o s t i c r e s u l t s is
a v a i l a b l e : C o n t i n u e d r e p e t i t i o n of one and
Trang 6the same e r r o r t y p e will cause t h e
e x p l a n a t i o n to focus on this category
Furthermore, the c o l l e c t e d i n f o r m a t i o n can
be u s e d t o g u i d e t h e t r a i n i n g strategy
E x e r c i s e g e n e r a t i o n m a y be c o n t r o l l e d to
just c o n c e n t r a t e on t h e w e a k p o i n t s of t h e
s t u d e n t or even to a l t e r the d e g r e e of
e x e r c i s e difficulty
VI E X P E R I M E N T A T I O N
To s t u d y some s e l e c t e d p r o b l e m s (espe-
c i a l l y the e x p l o i t a t i o n of h e u r i s t i c rules
w i t h i n the d i a g n o s i s and e x p l a n a t i o n
c o m p o n e n t s ) in g r e a t e r detail, a first
p r o t o t y p e has b e e n implemented C u r r e n t l y
the s y s t e m includes a r a n d o m s e n t e n c e
g e n e r a t o r to s u p p l y t h e s y s t e m prompts, a
s i m p l e p a t t e r n m a t c h e r for o b l i g a t o r y slot
variables, t h e t w o step d i a g n o s i s
d e s c r i b e d a b o v e and an e x p l a n a t i o n
c o m p o n e n t up t o the level of facts
The t r a i n i n g e x a m p l e s s t u d i e d so far
h a v e m a i n l y b e e n t a k e n f r o m the a r e a of
G e r m a n noun p h r a s e i n f l e c t i o n (indeed an
i n t r i c a t e s u b j e c t f r o m the f o r e i g n e { s
p o i n t of view) The e x p e r i m e n t s c o n f i r m e d
t h a t s i m p l e v e r s i o n s of t r a i n i n g e x e r c i s e s
m a y run a l r e a d y on v e r y c h e a p t y p e o f
h a r d w a r e (i.e 8 - b i t micros)
location of the e r r o r r a t h e r precisely (4) A model of the s t u d e n t % c a p a b i l i - ties is b u i l t up and t h e t e a c h e r is
s u p p l i e d with a s t a t i s t i c s in t e r m s of
l i n g u i s t i c c a t e g o r i e s even in t h e case of
v e r y c o m p l e x or m i x e d exercises
(5) I n s t e a d of e x p l i c i t l y l i s t i n g them,
e x e r c i s e s can be g e n e r a t e d a u t o m a t i c a l l y , thus a c h i e v i n g a v a r i e t y w h i c h a l m o s t
e x c l u d e s r e p e t i t i o n even in the c a s e of
e x t r e m e l y long or r e p e a t e d t r a i n i n g sessions
L i m i t a t i o n s for the a p p l i c a t i o n d o m a i n
m o s t l y r e s u l t from t h e f e a t u r e b a s e d
a p p r o a c h to k n o w l e d g e r e p r e s e n t a t i o n It first of all p r e d e s t i n e s the s o l u t i o n for
t h e t r a i n i n g of m o r p h o - s y n t a c t i c reg-
u l a r i t i e s (esp a g r e e m e n t relations) To
h a n d l e p r o b l e m s of e.g u s a g e or s t y l e in
a s u f f i c i e n t l y g e n e r a l m a n n e r seems to be far b e y o n d t h e c u r r e n t p o s s i b i l i t i e s
R E F E R E N C E S
VII D I S C U S S I O N
The d e s i g n of f o r e i g n l a n g u a g e t r a i n i n g
s y s t e m s b a s e d on f u n d a m e n t a l t e c h n i q u e s of
A u t o m a t e d R e a s o n i n g e x h i b i t s several
i m p o r t a n t a d v a n t a g e s as c o m p a r e d w i t h an
i m m e d i a t e i m p l e m e n t a t i o n of t h e a l m o s t
t r i v i a l s c h e m e a P a t t e r n Drill B o o k is
b a s e d upon:
(I) A u t o m a t e d R e a s o n i n g allows m o r e
flexibility Not the one c o r r e c t s o l u t i o n
is asked for The s t u d e n t m a y c h o o s e
h i s s o l u t i o n w i t h i n the l i m i t a t i o n s of
the d i c t i o n a r y ( e x p r e s s e d b y t h e e x e r c i s e
environment) D i a l o g s i t u a t i o n s m a y e a s i l y
be simulated E x p e r i m e n t a t i o n b e c o m e s
possible
(2) In a d d i t i o n to the r i g h t / w r o n g
d i a g n o s i s f u r t h e r t h r e e levels of e x p l a n a -
t i o n are available A c o r r e c t s o l u t i o n can
be g e n e r a t e d just for the p a r t i c u l a r w o r d
s a m p l e s c h o s e n b y t h e student
(3) It b e c o m e s p o s s i b l e to include
r a t h e r c o m p l e x r e g u l a r i t i e s b e t w e e n con-
text and s l o t variables N e v e r t h e l e s s ,
Barchan, J.; W o o d m a n s e e , B and Yazdani,
M (1985) C o m p u t e r A s s i s t e d I n s t r u c t i o n
u s i n g a F r e n c h G r a m m a r Analyser
R e s e a r c h R e p o r t 128, D e p a r t m e n t of
C o m p u t e r Science, U n i v e r s i t y of Exeter Kunze, J (1975) A b h ~ n g i g k e i t s g r a m m a t i k
s t u d i a g r a m m a t i c a XII, A k a d e m i e - V e r l a g , Berlin
Pulman, S.G (1984) L i m i t e d D o m a i n
S y s t e m for L a n g u a g e Teaching
P r o c e e d i n g s C o l i n g 84, Stanford: 84-87 RGdiger, B (1975) F l e x i v i s c h e und W o r t -
b i l d u n g s a n a l y s e des Deutschen
L i n g u i s t i s c h e Studien, R e i h e A, S o n d e r -
h e f t 1975, Berlin
S p r a c h t u t o r e n s y s t e m s fGr D e u t s c h als
F r e m d s p r a c h e , K I - R u n d b r i e f 44, J a n u a r 1987: 42
Wos, L.; Overbeek, R.; Lusk, E and Boyle,
J (1984) A u t o m a t e d Reasoning P r e n t i c e Hall, E n g l e w o o d Cliffs