CONTENT GUIDED ANSWER SEARCH SYSTEM 
FOR NATURAL LANGUAGES 
Peter KUmmel 
Institut fur Informatik 
Stuttgart University, FRG 
SUMMARY: 
Portions of natural language content 
must be directly related to memory func- 
tions in computers. A system should be 
selected which does not only fit theo- 
retically but also can be practically 6 
applied, due to its "natural" character. 
It represents a difficult task to cut 
away a usable model thesaurus from the 
huge meaning treasure of natural langu- s 
age. Air Traffic Control Language, re- 
stricted to Ground Control, serves this 
purpose. Due to severe realtime require- 
ment~ a limitation to conventional com- II/12113 
puters has been avoideo. Exclusively 3110 
content analoguous memory structures 
guarantee an automatic answer search, 
which obeys the realtime obligations of 
4-6 syllables/s speech veloscity and 
0.5-1.5 s response interval. 
GLOSSARY: 
Agglutination, agglutinated morphology= 
agglutinated expression structures of 
language = expression mixed with syn - 
tax particles, answer actualization, 
answer pool (AP), answer search logic 
(ASL), content unit = meaning, deuter = 
SVA which is defined after six sub-cri- 
teria, deuter-matcher, deuter-criterion 
: one of the six sub-criteria of one 
deuter, deuter string synthesizer DSS, 
feature extraction, flexion, content- 
unit = meaning = deuter plus syntagms, 
isolated morphology = language expres- 
sion existing mainly of deuter sequences. 
key feature of content KFC, KFC-matcher, 
lemma/ta = word stem, morphology = ex- 
pression structure of language, progres- 
sive agglutination, suffix = pre- or 
postponed syllable to word stems, SVA = 
substantive, verb, or adjective, if pos- 
sible in lemma shape, syntagm = consi- 
sting of syntax particles and syntax ru- 
les, syntax particle, syntax rule, twin 
KFC = a double KFC implemented into a 
ROM to match potential "input-KFCs" 
CR Categories: 3.65, 3.71, 3.74, 3.75, 
3.81, 5.32, 5.6, 7.3. 
1 INTRODUCTION: 
To substitute one partner n natural 
language dialogs by a computer, a model 
dialog should be chosen, which uses be- 
sides user utterances also system alerts 
for input. These alerts are triggered 
by the user's action. The introduced 
"Standard 80" thesaurus meets these de- 
mands. It concerns ground and ramp con- 
trol activities in ATCL dialogs between 
pilots and air controllers. In those 
Air ~raffic ~ontrol Language dialogs 
taxy procedures by the user, in this 
case the pilot, are in addition monito- 
red by sensors at the apron. Thus, besi- 
des "primary inputs" by pilot utteran- 
ces also "secondary inputs" by the sy- 
stem help the content guided answer 
search mechanism. The ATCL at interna- 
tional airports has been reduced to one 
--559-- 
particular language English - already 
in the fifties. In a minimum of time 
elapse a maximum of information flux be- 
tween the dialog partners is needed.This 
postulate causes all grammatical compo- 
nents with a low level efficiency rate 
to be abolished naturally. 
Considering most recent structural evalu- 
ations, formalization results of natural 6 
language led to the determination of : 
"key features of content; KFCs~I~y~ ~ a mat- 
ching procedure of input KFCs with twin 
KFCs stored in a ROM, prepared answers 
can be triggered. But, a match instruc- 
tion can be also used to trigger a se- 
quence of deuter, which are implemented 
in a time-analoguous read-only array.The 
trigger procedure of deuter sequences is 
faster than that of prepared answers. 
Especially if more voluminous thesauri 
are used But, up to the present, an ac- 
tualizing of deuter sequences is still 
missing proper morphological agglutina- 
tions. Automatically triggered deuter se- 
quences appear in isolated morphologies. 
For this purpose an "algorithm of pro- G 
gressive agglutination" is under consi- 
deration, by which syntax particles and 
additional syntax rules can be mingled 
into deuter sequences. For the ATCL how- 
ever deuter sequences without too many 
syntagms are quite sufficient. 
2 "STANDARD 80" A MODEL THESAURUS 
2.1 Alphabetical Sequence 
100 meanings = 82 deuter plus 18 syntax 
particles, ATCL, Ground Control, 121.9 
Mc, Stuttgart International Airport: in 
alphabetical order, syntax particles un- 
derlined: 
affirmative, airborne frequency, altime- 
ter setting, approved, apron, 6 Armycop- 
ter, backtrack, behind, 9 brake maifunc- 
tion, calling, call sign, caution, center 
line, Cessna 172, change to 118.8, char- 
lie, circle/circling, clearance, cleared 
to, construction work, contact radar 125. 
05, contact tower 118.8, continue, cor- 
rect, 25 crossing, D-EIPV, departing, de- 
parture route 28, exit point, expect le- 
vel change en route, 31 expedite, fire 
truck, flight level, follow, follome, 36 
for, go ahead, 38 goodbye, Hamburg air- 
port, helicopter, 41 hover, information, 
43 intersection, level change en route, 
Lima, local flight, Lufthansa Boing, 48 
Lufthansa 792, maintain, military air- 
craft 50, next, 52 November departure, 
on grass, 125.05, opposite direction,out, 
outbound, 58 over, Pan Am Clipper, par- 
king area, permission, please, position, 
64 present, QNH 1019 mb, 66 QNH 1009 mb, 
radar 125.05, ramp, ready to, readback, 
refueling, request, ro_r_o_~_e~_, runway 26, 75 
runway 08, say again, slow down, special 
VFR, standby, start up clearance, start 
up engines, stay clear off, stop, 84 
Stuttgart Tower, takeoff, taxy clearance, 
taxy/taxying, this is, to the West, 90 
type of aircraft, 91 via departure route, 
wait, we are, what, when airborne call 
radar 125.05, when ready, wilco, 98 wind, 
99 you are, I00 0493 PA. 
Appearing numbers within the deuter ac- 
cumulation in alphabetical order, are 
interim counts from i to I00. 
18 Syntax Particles: 
1. affirmative, 2. approved, 3. correct, 
4. for, 5. go ahead, 6. goodbye, 7. next, 
8. out, 9. over, I0. please, 11. roger, 
12. standby, 13. this is, 14. we are, 15. 
what, 16. when ready, 17. wilco, 18. you 
are. 
---560 
2,2 The Eight Partial Dialogs: 
Partial Dialog NO. 1: VFR Clearance: Grass - Ramp 
Ground Centrol, 121.9 MC, Stuttgart Stgt. International Airport 
Aircraft: Cessna 172, D-EIPV 
• ( 
Partial Dialog No. 3: VFR Taxy Procedure} Ramp - Runway i 
GroLmd Control, 121.9 Mc, Stuttgart (Stgt.l International Airport 
Aircraft: Cessna 172, D-RIPV 
)' "3 
> • 
Partial Dialog NO. 2 : VFR Clearance: Ramp - Runway 
Ground Control, 121.9 MC, Stuttqart (Stgt.) International Airport 
AirCraft: Cessna 172, D-EIPV 
( • 
Partial Dialog No. 4: VFR Taxy Procedure: Ramp - Runway II 
Ground Control, 121,9 MC, Stuttgart (Stgt.) International Airport 
Aircraft= Cessna 172, D-EIPV 
> • 
> • 
• < 
--561-- 
Partial Dialog NO. 5: VFR Taxy Procedure: Ramp - Runway llI 
Ground Control, 121.9 Mc, Stuttgart (Stgt.) International Airport 
(Brake Malfunction), Aircraft: Cessna 172, D-gIPV 
~ ~rti,~l Dialog NO. 7 : IPR Taxy- and En Route Clearance: Ramp~RnnWay 
Ground Contr<~l, 121.9 Me. Stuttgart (Stgt,), Inturnational Airport 
US Army Plight to FrankfL~rt 
~~~in el~~jalrborn e . r u charli(~ 
< < 
Partial Dialog NO. 6 : VPR llover Procedure to llelicopter Circle and 
Takeoff, Ground Control, 121.9 Mc, Stuttgart, International Airport 
US Army Helicopter: U\[I I , 15605 a 
irnlycopte 
~ 3 
~ 6 
Parhial Dialog NO. 8: IFR Taxy- and En Route Clearanco: Ramp-Runw~*y 
Ground Control, 121.9 Mc, Stuttgart {stgt.}, International Airport 
Lufthansa DOmestic Flight: Stuttgart-Hamburg 
--562-- 
2.3 Major Syntax Rules in the Standard80 
1 Talk and requests are only permitted, 
if the line is empty. 
2 Confirmation of instruction is possib- 
le by repetition of the instruction, 
or major parts in it. 
3) Subject/Predicate-Sequence (SP). 
4) Confirmation of partner utterance by 
stating the last two letters of the 
aircraft identification. 
5 Abbreviation of high frequency phra- 
ses to short expressions: examples: 
"will comply with" to "wilco" and 
"understood" to "roger". 
6 Extension of easy misunderstood high 
frequency syntax particles, e.g."no" 
to "negative" and "yes" to "positive" 
or "affirmative" 
7 All dialogs should not contain more 
than six cycles (dialog cycles). 
8) All dialogs should not contain more 
than six input- and six output deuter 
except for en route clearances. 
9 Absolute obligation of pilot to con- 
firm QNH-data. 
I0) Urgent obligation to confirm the: 
"change to 118.8" or "118.8" the 
runway frequency as a sign, the dia- 
log is finished. 
II After the second cycle the aircraft 
identification should be abbreviated 
from e.g "D-EIPV" to "D-PV". 
12) Each tower utterance should possibly 
commence with the aircraft identifi- 
cation. 
3 LANGUAGE COMPONENTS AND THEIR TERMINO- 
LOGY 
3.1 Content Units (meanings) 
A natural language L n expression thesau- 
rus can be split into a) a group of sub- 
stantiva verba, and adjectiva 6 , , the SVAs 
and b) a group of syntagms (Fig. i). If 
the SVAs, possibly in lemma shape, are 
FIG, i 
ANALYSIS OF " MEANINGS " 
SVA 
DEUTER 
MEANINGS ~.~ S SYNTAGMS 
y ' SYNTAX SYNTAX 
PARTICLES |RULES 
defined after their sub-criteria, the 
deuter_criteria6,1~hey. 4 are called "deuter" 
3.2 The Six Deuter-Criteria: 6 
1) Identity: given by DC-enumeration. 
2) Age: absolute and relative, also in 
comparison to dialog cycles. 
3) Association: A v and A h, vertical and 
horizontal, A v is to compare 
with edges in a directed graph. 
4) Frequency: absolute and relative, is 
in smaller thesauri related to 
the significance value. 
5) Significance: has influence on syntax 
rules and their deuter, e.g. 
No. 9, (2.3) very high value. 
6) Truth: also existent in smaller dia- 
logs. If untrue utterances by the 
pilot are given as e.g."mercedes 
benz" after the tower inquiry: 
"type of aircraft?" or, "profane" 
utterances like: idiot, nonsense, 
etc. They are not permitted and 
thus "untrue" 
3.3 Syntagms 
3.3.1 Definition: Syntax Particle 
Excluding SVA-Lemmata, all suffixes, 
flexions, and remaining words of an L n 
thesaurus are considered Syntax Particles. 
3.3.2 Definition: Syntax Rule 
They include rules of word sequences:S/P, 
S/O/P etc. and can be directly related 
to rules of dialog functions. 
--563-- 
4 STRUCTURE AND FUNCTION OF DIALOG CYCLES 
4.1 User inputs: a) identific., b) iden- 
tific.+request, c) request, d) instruc- 
tion confirmation, e) wrong instruction 
confirmation and f) unclear identific. 
4.2 System inputs: a) interrupt, b), c), 
d) three different "wrong user actions" 
4.3 System Outputs: a) instruction to 
continue (4.1a), b) instruction + permis- 
sion (4.1b,c,d), c) correction (4.1e), 
d) request for correct identific. (4.1f), 
e) standby instruct. (4.2a), f) correc- 
tion to (4.2b), g) correction to (4.2c), 
and h) correction to (4.2d). 
4.4 Determining the KFCs: 
Depending from the deuter-criterion:age- 
value, the dialog cycles 1-6 from old to 
new are brought into relation to the sum 
of all potential partial dialogs, in this 
case 8. Among all cycles of the same age, 
frequency values and redundancies of sing- 
le deuter are checked. Only a few deuter 
among all input data have the "switching 
ability" to select one of the 8 potenti- 
al next cycles. These account for less 
than 20% of all input data. They are cal- 
led "key features of content", KFCs. 
5.ANSWER SEARCH LOGIC FOR PREPARED 
ANSWERS (ASL) 
5.1 Match Procedures MPs of KFCs: 
According to 4.4, all potential KFCs are 
implemented as "twin-KFCs" in a twin-ROM. 
The implementation array is time-analo- 
guos. As the input-KFCs appear also af- 
ter the deuter-criterion age-value, a 
realtime MP will be quite simple. 
FIG, 2 SEQUENTIAL NETW, OF AT 
7!<<~ b~----<~\]----- 
\[_ ~zLgL_:~D---D----~ .... 
5.2 Trigger of prepared answers AT 
As each dialog cycle of the eight dia- 
logs consists of a) inputs and b) out- 
puts, the dialog outputs (air controller 
utterances) can be easily copied for pre- 
FIG, 3 ASL - ARCHITECTURE : 
system internal 
sensor input~ 
/ Coder 
Speech Analyzer 
ROM for J TWIN I 
KFC s I 
~V-- 
A 
T =~KFC F=== 
Matcher 
| .......... -7/ .......... J 
Answer Trigger 
Speech Synthesizer 
/ Amplifier / 
i I Answer Pool for prep. 
Answers including 
Deuter - Coder 
--564 
pared answers. They are triggered, if 
KFC match procedures MPs and system in- 
ternal sensor inputs passed a sequential 
network AT. According to the 8 partial 
dialogs PDs, 7 switching combinations 
are possible:i) MP of I input KFC (PD6), 
2) MP of 2 input KFCs (PDs 1,2,7,8), 3) 
MP of one among 2 input KFCs (e.g. in cyc- 
les 2-6), 4) interrupt (PD 1), 5) MP of 
I input-KFC + i of 3 systeminternal alerts 
No I, 6) like 5) No II, 7) like 5) No III. 
5.3 Sequential Network of AT 
According to 5.2, for each Partial Dialog 
7 potential switching combinations are 
possible (Fig. 2). 
5.4 Components of the ASL 
The main units consist of a) a ROM for 
twin-KFCs, b) a KFC-matcher as a compara- 
tor device to match input-KFCs with twin- 
KFCs, and c) an AT (Fig, 3). 
6 DEUTER STRING SYNTHESIZER DSS 
6.1 Function of a DSS 
According to function- and memory redun- 
dancies in ASLs, (Fig. 3), the units: 
I) KFC Twin ROM, 
2) KFC Matcher 
3) Answer Trigger, and 
4) Answer Pool for Prepared Answers, 
are combined in a "DSS-Logic". Not only 
twin-KFCs but all potential deuter in all 
dialogs are stored in the DSS-Logic. 
This, in a way, substitutes the Answer 
Pool for prepared answers. The read only 
memory implementation must be in geomet- 
ric "time logic". Thus an electrical ac- 
tivation of one matched twin-KFC trigge- 
res a sequence of surrounding stored deu- 
ter. This triggering is executed by a 
"switsch thru-", a "put through connec- 
tion" procedure. Each actualized deuter 
in such a "switch thru sequence" is si- 
multaneously transformed into an audio 
output, a synchronous "read out" The 
"switch thru association" becomes "loud 
thinking". This fits a logic answer to 
the input-KFCs. Major functions of the 
DSS are: 
I) All twin-KFCs serve potential match 
procedures with input-KFCs. 
2) After an input-KFC is matched, the 
matched twin-KFC is activated as "the 
first deuter" in a triggered deuter se- 
quence. 
3) The length of the sequence will be 
limited from 3 to I0 deuter. 
4) Each connected deuter in a triggered 
deuter sequence is allocated with 2-3 
seconds time, in which the adequate 
English utterance can be expressed by 
a speech synthesizer device. 
5) The "switch thru connection" to neigh- 
bouring deuter in the deuter sequence 
continues only, after the English 
word of the last deuter is spoken out. 
6.2 Architecture of a DSS 
The array of DSS content is divided into 
dialog cycle sections. For each of them 
five or more KFC-Match/Trigger Stations 
(Mattrigs) are provided. Structure and 
organization of function units in all 
first dialog cycles of the eight model 
dialogs are shown in Fig. 4: If such sec- 
tions for the remaining dialog cycles 
2-6 of all potential dialogs are compi- 
led in an analoguous way and put toge- 
ther, a further elimination of redundant 
portions will help to create a complex 
DSS architecture. 
Acknowledgements: 
By courtesy of the "Bundesanstalt fur 
Flugsicherung" in Frankfurt/M, the author 
has been permitted to copy tapes at the 
air traffic control center at Stuttgart 
--565-- 
FIG, 4 SECTION ONE OF ALL FIRST DIALOG CYCLES 
user input~--~ 
syst. intern.inout 
StationNo: 
MPs = matcH)revi. 
Procedures :! I D-Know 
ledge 
1,, 
Model 2. 
Dialogs ~, x 
i 8 4 x uS • x-- 
6. 
7, 
8. 
Trigger User-ID 
Procedure 
spoken Output: 
~--~-~-~-~ 
Mattrig I 
syst. int. 
Inp.+alerts 
PDs 1,3,4,5 
O~ 
0 -'---, 
0 -.-, 
~0" 
T 
User-ID + 
corrected 
alerts PDq 
3:4~ 
\ 
Mattrig 2 
User-ID + 
interrupts 
PD I 
~x. 
User-ID + 
standby in- 
struction 
PD I 
% 
Mattrig 3 
solely 
User-ID 
PD 2 
x~ 
I 
User-ID + 
go ahead in 
struction 
PD 2 
Mattrig 4 
wrong 
User-ID 
PD 6 
x I 
k___ 
Mattrig 5 
User-ID + 
request 
PDs 7,8 
x I x$ .... 
repetition User-ID + 
.of wrong request 
User-ID approval 
PD 6 PDs 7,8 
Echterdingen, International Airport for s 
statistical thesaurus evaluations A re- 
search project sponsored by the "Deut- 
sche Forschungsgemeinschaft" in Bonn, 
under the topic: "Answer Searcher" is 
supervised by the author. 
7 Conclusion: 
Function simulation of one partner in 
nat. lango dialogs by a machine demands 
the following major procedures: 
I) KFC-matching of Input-KFCs with Twin- 
KFCs implemented in a ROM, 
2) Answer Trigger according to KFC match 
procedures in devices with prepared 
answers ASLs, and 
3) Actualization of Deuter String Out- 
puts in DSSs after KFC matchings. 
More than expected, complex evaluations 
of nat. lang. phenomena were necessary 
for memory array purposes. Among them 
particularly the six deuter-criteria. 
But also a sufficient familiarity with 
the applied thesaurus was necessary. 
Since 16 years the author holds a valid 
PPI license and executes active flying. 

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