DESCRIPTION STR.ATEGIE.S FOR NAIVE AND EXPERT USERS 
C~cile L. Paris 
Department of Computer Science 
Columbia University 
New York, NY 10027 
Abstract 
It is widely recognized that a question-answerlng 
system should be able to tailor its answers to the user. 
One of the dimensions Mong which thus tailoring can 
occur is with respect to the level of knowledge of a 
user about a domain. In particular, responses should 
be different depending on whether they are addressed 
to ns/ve or expert users. To understand what those 
differences should be, we a~alyzed texts from adult 
and iunior encyclopedias. We found that two different 
strategies were used in describing complex physical 
obiects to juniors and adults. We show how these 
strategies have been implemented on a test database. 
INTRODUCTION 
Whether the purpose of a natural language program 
Ls to ease man-machine interactions \[Kaplan 82; Hayes 
and Reddy 79\] or to model human communication 
~Lehnert 781, it must take into conslder~tion certain 
characteristics of the person engaged in the interaction. 
\[n an interaction between people, the goals, beliefs, 
retentions, knowledge and past experience of the 
participants will play a role in how they communicate 
with each other \[Cohen and Perrault 791, \[Perrault and 
Allen 80\[. Similarly, those characteristics should play 
a role in the way a computer system interacts with a 
user. In particular, a questlon-answering program that 
provides access to a large amount of data to many 
different users will be most useful if it can tailor its 
answers to each user. 
We are interested here in how the level of 
knowledge (or expertise) of the user a~fects an answer. 
As an example of this kind of tailoring in a naturally 
occurring conversation, an explanation of how a car 
engine works a~med a~ ~ child wdl be different than 
one ~med ~tt an adult, and an explanation adequate 
for a music student is probably not quite sufficient for 
a student in mechanic~l engineering. \[n this paper, we 
study the strategies used tn natural language to 
describe physical objects to two different types of 
users: naive and expert. By naive ~nd expert, we 
refer to how familiar a user m about the domain of 
the database as opposed to how experienced the user 
is with the question/aJnswering system. When the 
database ts complex, it becomes important to vary the 
level and the kind of details included in the answer in 
order to provide an answer that caa be best 
understood by the user. 
We plan to use this distinction in the question- 
answering program for RESEARCHER, a system being 
developed at Columbia University. RESEARCHER 
reads, remembers, and generalizes from patents 
abstracts written in English \[Lebowitz 83\]. The 
abstracts descrlbe complex physical objects in which 
spatial and functional relations are important. Thus, 
we are interested in characterizing spatial strategies 
that can be used for experts and novices about certmn 
physical obiects. We give deta41s in the paper of the 
current implementation of description strategies on a 
test database of object descriptions. 
OUR DOMAIN 
Our goal is to characterize some of the strategies 
employed to describe complex physical objects and see 
whether these strategles are different for naive and 
experts users. To investigate thus problem, we have 
looked at texts from encyclopedias {botih adult and 
junior) and high school physics textbooks ~. The texts 
we have studied are about physlc~l objects performing 
a function (such as telephoues and telescopes), and 
generally do not exceed several paragraphs in length. 
These texts make the distinction between na4ve and 
expert readers ~nd have been widely used for a 
number of years for those audiences. They provide 
examples of different descriptive strategies that actually 
occur in natural language. Thus, a question-answering 
system should be able to reproduce them-'. 
Studying texts from encyclopedias gives us the 
advantage of being able to compare descriptions of 
identical objects aimed at two distinct audiences. On 
the average, a younger audience has had less 
opportunity to gather experience and knowledge about 
any. particular doma4n. Thus a younger audience as a 
-whole is more naive about ~ domain than an adult 
audience. Hence, these texts give us a good starting 
point for studying the differences between the 
IWe studied about fifteen examples from each encyclopedia and textbook. 
2Our goal however, is not to study, how effective these tex~s ~re for different human rea(iers. If further 
psychologlcal research shows that other distinctions ~.re • ppropriate, they could be . incorpoTated.. . The 
dustinction based on encyclppedias and textbooks is • really the only available at thls point. 
238 
1) The hand-sets introduced in 1947 consist of a receiver and A transmitter in a single housing available in 
,black or colored plustic. 
2) The transmitter diaphragm is clamped rigidly at its edges 3) to improve the high frequency response. 
4) The diaphragm is coupled to a doubly resonant system 5) -s cavity and an air chamber- 0) which 
broadens the response. 7) The carbon chamber contains carbon granules, 8) the contact resistance of 
which is varied by the diaphragm's vibration. 
g) The receiver includes a ring-shaped magnet system around a coil and a ring shaped armature of 
anadium Permendur. 10) Current in the coil makes the armature vibrate in the air gap. 11) An attached 
phenolic-impregnated fabric diaphragm, shaped like a dome, 12) vibrates and sets the air in the canal of 
the ear in motion. 
I. Constituency 
Depth.attributive for the tronamitt~ Depth-attributive far the receiver 
(Description of the trQnamitt~) (Description o\[ the receiver) 
2. Depth-Attributive 9. Depth-Attributive 
3. Cause-effect 10. Cause-effect 
4. Depth-Attributive 11. Attributive 
5. Depth-identiflcation 12. Ca-,e-effect 
8. Cause-effect 
7. Depth-Attributive 
8. Cause-effect 
F|gure is Constituency Schema Example 
aescnpttons given to naive users and those glven to 
experts in the domain. To minimize the effects of 
styiistlc differences on our results, we chose texts from 
several different encyclopedias in each audience 
category. 
THE TEXTUAL ANALYSIS 
We began by analyzing the different texts using 
methods developed by other researchers ( \[Hobbs 78a), 
\[Hobbs 80l, \[Mann 84\], \[McKeown 82\]) we 
decomposed paragraphs in terms of their pmmitwe 
rhetorical structure ia an attempt to find a consistent 
structure tn each group of texts. The analy.~s showed 
the adult encyclopedia descriptions to be mainly m 
terms of the sub-parts of the object being descrlbed 
These texts can be characterized by one of the textual 
structures posited tn \[McKe0wn 82\], the constituency 
schema. This structure is presented m the next 
section. On the other hand, no schema or other 
organizing structure consistently accounted for the 
descrlptmns m the junior encyclopedia texts In 
looking for other types of organizing srrategles, we 
discovered that the ma~n strategy m descrlbmg cblects 
to a naive user is to trace through the process that 
allows the obiect to perform Lts function. 
Strategy for the Adults 
The descriptions from the adult encyclopedias tend to 
follow the pattern estabhshed by the constltuency 
schema, one of the textual structures defined m 
\[McKeown 82\[. In her work on natural language 
generation, McKeown studied the problems of what to 
say and how to organize text coherently. She 
examined texts and transcripts, classifying _ each 
sentence as one of a set of rhetorical predicates 3 and 
found that some comblnatmns of predicates were more 
likely, to occur than others. Moreover. for each 
discourse sltuation, some combination would be the 
most appropriate one. Those standard combinations 
were encoded as schemas which axe associated wlth a 
particular dLscourse situation. One of these schemas is 
the constltuency schema which is used to descrlbe an 
object (or concept) m terms of its subparts and their 
properties. The constituency schema is shown below ~ 
(For a given entity, Constituency LS the description of 
its sub-parts or sub-types, and the attributive predicate 
glees properties associated with it.) 
3Rhetorical predicates characterlze the structural purpose of a sentence and have been discussed b~" a 
vamety of linguists \[Grimes 75\] fHobbs 78b| S6me examples are constituency (describtlon of sub-parts or 
sub-types), attributive (providing detad about an entity or event) and analafy (-the making of an analogy). 
4We have altered McKeown's constituency schema slightly by making the first predicate optionkl Instead. 
of mandatory: in the texts studied, the main parts o{ the object were not necessarily immediately lis~ed. We 
,~,e using McKeown's notation:" {}" mdicatd optlonality, 'p indicates alternatives, "÷" indicates that the item 
may appear 1-n times, and "*~ indicates that the item may appear 0-n times. Finally, ";" is used to represent 
clszsificatlon of ambiguous propositions. 
239 
=_ 
L l)W~en one speaks Into the transmitter of a modetqt telephone, these sound waves strike 
a~galnst an aluminium diak or diaphra~n and eause it to vibrate back and forth In Just the 
~me way the molecules of air m~ vibrating. 
IT. 2) The center o/ thin diaphra~nn ia connected with the carbon button originally invented 
b~ Thomas A. Edieon. 3) Thi~ ie a little buns, bo: filled with granules o/carbon composed 
of eapeciall;; ~dccted and treated coM. 4) The front end back of the button are inaulntcd. 
Ill. 5) The talking eu~ent Is paNed through this box so that the eleetrlelty must find Its 
way from gs~nule to g~qmule luside the box. 6) When the diaphragm moves Inwm~l under 
the pressure f~om the sound waves the e~bon g~dn~ are pushed together and the eleetrlelty 
finds an ea~le~ path. ~) Thus s strong eurtent flows through the line. 8) When a thin 
im~t|on of the sound wave comes along, the diaphragm sprln~ back, allowing the e~bon 
pm'tleles to be mote loosely packed, and eonsequently less eu~.ent can find Its way through. 
g) So s varying or undulating current Is sen~ ove~ the line whuse vibrations exactly 
eorr~pond to the vibrations caused by the speaker's volee. 10) ThIs euetent then flows 
through the line to the colic of an elcctromafnet in the receieer. 
IV. 11) Ve~ near to the pa/u of thie magnet i, a thin iron di~e 
V 12) When the eurtent becomes stt, onge~ it pulls the disc toward it. 13) As s weaker 
eur~ent flows through the resigner, It Is not strong enough to att~set the dlsk sad It springs 
back. 14) Thus the dlaphrs~m In the receiver Is made to vibrate In and out .... 
Flgute 2: Text from ,~ junior encyelopedi,~ 
Constituency Schema 
{Constituency} 
Cause-effect \] Attributlve* 
{ Depth-ldentlficatlon \] Depth-attrlbutlve 
{ P~rtlcular lllustratlon / Evldence} 
{ Comparison , Analogy} }+ 
{ Amplificatlon / Explanation 
/ Attributive \[ Analogy } 
Consider for example the descnptlon of a telephone 
from an, adult encyclopedia \[Colher 62\] shown in 
Fzgure 1 ~. In the first sentence, the telephone is 
described In terms of its constltuency (or sub-p~xts}: 
the transmitter, the receiver and the housing From 
s~ntence 2 to 8, attributive reformation (or 
properties) ~s well as functlonM Info~matlon (cause- 
effect) about the transmltter axe glven ~ Finally, the 
recelver ~n turn ~s described from sentence 9 to 12, 
uslng both attributive and c~use-efrect information. 
SFor clarity, the original one paragraph text has been divided mto three paragraphs. 
SThe reader who is familiar with this type of ~nalysm will note that several properties bf the 
transmitter are in turn identified and described uslng attributive reformation which is a form of schema 
regnrs|on, 
Entries in the junior encyelopedla ~nd hlgh 
school text books 
In texts aimed toward younger audiences, an object 
is m~nly described in terms of the functions of its 
parts. The description traces through the process 
reformation instead of an enumeration of its sub-parts, 
• s is usuMly the case in the adult descriptions. The 
p~rts are mentloned only when they" need to be, that 
is, when the descnption of the mechanical process calls 
for them. As an example of this phenomenon, 
consider the description of a telephone show.n tn 
Figure 2, taken thls tIJne from the encyclopedia lunior 
\[Bntanmc~-Junior 6,3\]' : 
We see that the theme of this text is the 
mechanlcM process description shown in bold face. 
That process descnptlon gets interrupted when 
descnptlve informatlon can be included concerning 
sub-paxt that was just mentioned as part of the 
process descnption. Such information Is shown zn 
indented it~lics in the example. 
Furthermore, we see that, in the junior 
encyclopedla, not only ts the description made mainly 
through a process trace, but there are no large gaps in 
7the original entrv contalned the two paragraphs. The second one has been dlvlded for clarity 
240 
; Description of the TELEFHOKE btaed on the Constituency uchens. 
.u~wY axe the unique identifiers fur the object frtae8. 
i The Constituency gchen& vu filled by eteppxng throuKh in ATH. 
tasvor : 
~ (TE.EPHO~) I elDENTIFICATIONe (VARIART-OF: DEVICE#)) 
• CONSTITU~CT, (/~i\]2 (l'RA~S311t~..~)) (~w~t6 (HOUSIMG)) 
(~mrutS (LINE)) (Jem:'~t7 (RECF.IVER))) 
The telephone is 
• device. It consists 
of t traflenittUro 
• houaing. • line tad 
n ruceiTer. 
(7R.~I~) ; The tranntttur t8 I ,IDE~TIFICATION* (VABIAKr-0F: "fIUtl~MITl'~8)) ; • kind of 
traamLttter. 8COMSTITUENCTe 
(~8 (DOU~LT-RESONA~'r-S'fS'r~)): It h "~ • doubly (J~13 (DIAPHRWm-T))) 
i /dlnil6 ~HOUSING) t~e housing is (e\[D~rrlFICATIONe (VARIAFI*-0F: COVERS)) ; • type of 
cover: (,@NSTITUENCY*) 
fdf~f5 (LINE) ; the line is • rite; I eIDEFI'IFICATIONe (VkI~IAFr-0F: lll~#)) 
*CONSTITUE~CT=) 
• u~r~17 (RECEIVe3) *IDENTIFICATION8 (VARIAFr-OF: RECEIVIng)) 
• CONSTII"UENCT* (~ME\]i22 (DIAPHRAGM-T)) (&~21 (AIR-GAP)) 
(~v~18 (F.LEC~OMAG~:'r))) 
The receiver te 
kind of receiver. It 
¢ou8i8~8 of • dl&phr~pt. ~ sir ~tp 
-~d ,~ electronwrnet. 
Figure 3s Printout of the Constituency Schem~ Example 
the chain of references Almost everyttung is spelled 
out. Consader the third paragraph of the text glven 
~bove where every step s explained: 
"The talking current is passed through this box 
SO THAT the electricity must find its way 
FROM GRANULE TO GRANULE inslde the box." 
From there, the writer goes on to explaan how the 
electricity passes through the carbon box, once again 
stepping through the process, spelhng out the 
consequences of e~ch step: 
"When the diaphragm moves inward under the 
pressure f~m the sound waves the carbon 
grains are pushed together and the electricity 
finds an easier path. THUS a strong current 
flows through the line." 
Contrast this detmled procpcr~s descnptmn with the 
descriptmn given for an adult": 
"The carbon chamber contains carbon granules, 
the contact resistance of which is varied by the 
dlaphragm's v|bration'. 
Other differences occurred between the jumor and 
adult entries as well. In general, more vlsual 
tnformatlon was included m the text for the junior, so 
as to render the description more vlvld. For exampl e, 
the carbon button in the telephone descnptlon Is 
described as "a !ittle brass box filled wlth carbon of 
especlally selected and treated coal" m the junior 
8This excerpt is taken from an adult encyclopedia. 
encyclopedia, in contrast to "the carbon chamber 
contains granules" m the adult encyclopedia, similarly, 
the junior entry for light bulbs describes a filament as 
a "fine run.ten filament wound m very small coils", 
whereas the adult encyclopedi~ mentlons only "~ coded 
tungsten filament." 
Another malor difference was that the lumor 
encyciopedi~ texts had a higher degree of redundancy 
while the adult encyclopedia ones were quite concise 
We refer to the jumor telephone example again to 
illustrate this point: sentences $ and 6 explained how 
the electnclty Is made to flow easily through the box 
Sentence 7 xs a recapttulatlon of that phenomenon. 
Finally, sentence 8 explains the reverse effect 
Finally, we observed that expository style and 
vocabulary differed considerably m the two types of 
texts studied. Future research will attempt to 
characterize these phenomena. 
COMPUTATIONAL USE OF TIlE 
STRATEGIES 
The strategies are currently ~mplemented on ~ test 
database composed of oblect descriptions from the 
encyclopedias. The representation of an object thus 
contains all the reformation included for that 
part:cular oblect m both encyclopedl~. The two 
241 
Tan process inforlation gets picked up tad printed out for t naive user. are the unique identifiers to the fruen corresponding to the 
nets-relations the program is ~racing. 
*(print-process (ge~-procen 'J".eml\] 
tREI.3 (P-SPEAKS-INTO) : ; Ihen one speaks %nee t.he 
objectSUbject : (~liEi127)(tliE~) \[TRANSXITT~\]\[OME\] ; ~raaalLitter of a ~elephonu, 
~ /d~O (M-CAUSES} 
IREL4 (P-HITS) : subject,: (/t\]l~28) \[SOUNOIAVF.~\] 
objec~ (JM~i3) \[DIAPHRAGM* T\] 
~REL4 (P-HITS): ; Thin ¢aunen subject: (/tI~128) \[SOtrNDIAVF..~\] ; 
object (adCE~) \[D IAM~tG\]I-T\] 
m~ /l~l (M-CXUSE$} 
tREI.fi (P-VIBRAT'r~) ; the ditphra4Sm to vibrae-e cub j ect 
object (grief3) \[DI~GII-T\] 
I~EL5 (P-VIBI~IT.$) subject. 
object. (/tiiE~) \[DIAPHRACII-T\] 
:=~> /Ida2 (M-EIIUIVALENT-TO} ; in the s~ute manner am 
/d~L8 (P-¥1BRAT'r..~) ; the molecules of ear eubj oct : vibr~tia K. 
ob\] oct, (IM\]~2S) UtlR-IIO~\] 
; the sound vavee bi~ 
; ~-~e 4iapbr~4p| of the ~ransmit~er. 
Flfure 4: Printout of the Process Tr~ce 
strategies presented dlctate what informatmn to snclude 
from the knowledge base, based on the constituency 
schema _or the process trace ~ shown in Figures 3, 
4 and SY 
Knowledge-based rep~seutat|on 
We use a frame-based knowledge representatmn - 
\[Wasserman and Lebowitz 83; Wasserman 85} m 
which the basic frame represents an oblect These 
structures are the entitles in a generalizatmn hierarchy 
In additmn to the generalization, or instance-of links, 
there exist two additional kinds of links ioming 
entlties: part-of links, which indicate an entlty is a 
part of a larger structure, and relations, whlch convey 
mformatmn about spatlal or functional reiattonshlps 
Finally, there ,~re causal links between relations called 
meta.relations. 
9Further work is needed to fully implement the schema predicates and add more descnptlve 
mlormatlon 
Implementlon of the adult encyclopedia strategy 
For an adult, the program {~ls the constituency 
schema, ~ shown In Figure 3An_ The predicates 
contained m the schema define the type of mformatmn 
to be taken from the database. The figure shows the 
final output. The entities are represented by thelr 
unique identlfier &MENLX:, and the predicates are the 
starred items (e.g. *IDENTIFICATION'). The 
hypothetical english output is included in the 
comments. 
The identification predicate represents the more 
general concept of which the present ob|ect ts ~n 
mstance Because the test database mcludes only the 
mformatmn contained In the texts read, the hierarchy 
may not be complete for all objects. As ~n example, 
a transmitter was never defmed m terms of a more 
general device, and thus has no super-ordm~te The 
constituency predicate gives the components of ~a 
entity, if there are any 
lOSes \[McKeown 801 for details of ~ stmdar system. 
242 " 
i nov the pro~rta taken each relation which can be dirlded into subnteps 
and ~racen ~hrough that each step. An this case, aBF.LS (P-VIBRATES) can be broken up 
into aBELS (P-MOVESoFOR|ARD) and aBEL7 (P-MOVES-BACAIARD). 
aBEL18 (P-INCREASES}: ; The increased sound yarns 
subject ; : intensity object (/~I~128) \[$OU~DIIAVE- I FINNS l I'T\] 
m> ~U~3 (M-CAUSES} ; cannes 
aBEL8 (P-MOV'r.3-FORUARD): ; the diLphrq;m subject : ; to Boys forv~rd 
objeo~ (~) \[DIAFHRXQ/-T\] 
aBEL8 (P-IfOVES-FORUARD) : 
subiect : objec~ (aBe3) \[DI~OtAGX-T\] 
m> 4dm4 {M'~US~5) ; vhtCh causes 
aBE~28 (P..COMPRF.SSF.S) : : the ~rl~lule8 £a the carbon 
chamber to be conpreased. subject : object (J*Vl~l 2) \[GRANULE\] 
aBEL2S (P-C~MFR£SST~) : 
subject : object (~i\]~112) \[GRMIUt~\] 
m> fd~S {M-CAU~£S) ; A8 a rasult. 
8REL22 (P-OECREASES): ; their contact resis~snce subject : : decreases. 
object (*re:lit3) \[CONTACT-RESI ST~CE\] 
aB\[1,22 (P-OEC~EASF.3) : subject : 
objec~ (,I~E\]i13) \[COFFACT - RF..S l S'L4JIC~ 
=~> #J~8 (\]I-CXUS'r~} ; -,,d cannen 
aBEL24 (P-INCRF./i3~): ; the curren~ to increase. subject : 
object (/rMEM31) \[CU?~I~I'- I h'l'l~S l TI' \] 
i The prosrus trace8 throug~ in the same manner for each relation ~avin~ 
substeps. 
FIKu~e $, Printou~ of the Process Trace (cont'd) 
Junior encyclopedia strategy 
For the junior, the strategy dictates to fol!ow the 
cause-effects links in the knowledge b~se ,n order t,o 
trace the process. In our representatlon, th~se causual 
links are named meta-relauons (In the figure, they 
are represented by the Identlflers &:MRX. &RELX 
correspond to the reiauons, l e the spatlal or funcUonal 
l,nks between entltles ). The program traces through 
the meta-relatlons, ptcklnK the process informatlon as 
shown m Fisure 4. When .~ relatlon can be broken 
into substeps, the program then traces through those 
sub-steps (see Figure S). 
Future Work 
There axe severM theoreticM msues that need to be 
addressed. In our test dat~ba.se, the problem of 
declding m what order relations occur does not arise. 
However, for an arbitrary database, knowmg where to 
begs describing a process may be more difficult 
Simllaxly, the process may not be as sequential ~s the 
ones we examined so fax, and, as a result, we plan on 
further study of how to organize the informaUon. 
Furthermore, in our test database, we don't need tc 
conszder how deep into the substeps the process 
description should go, but this Issue exists for an 
arbitraxy database. Finally, we have looked at the 
two ends of a spectrum (n~ve and expert), but, for 
users not at either of these ends, we must consider 
how to combine these strategies. 
243 
We have started to address the problem of 
generating natural language for the descriptions. We 
have begun the augmentation of an English surface 
generator \]McKeown 82\] that, using • functional 
grammar \[Kay 79\], takes the output of the textual 
component to translate it into English sentences "'. 
However, how this program may interface with the 
strategies remains to be studied. 
CONCLUSION 
It is important to tailor a system's response to the 
level of expertme of the user. By studying texts aimed 
at two different levels of readers, we have found that 
two different strategies were used in describing 
physical objects, depending on whether the description 
was for an adult or for a junior. For an adult, an 
object is described with its sub-parts and their 
properties; for a junior, the description traces through 
the mechanical process which renders the object 
functional. 
The two strategies presented account for the mare 
differences found between the adult and jumor entries. 
This turns out not to consist of merely glving more 
details for the expert ~ m often thought \[Wallis and 
Shortliffe 82\]. \[n the adult entries, details given are 
mainly about the sub-parts and thelr properties and 
less about the mechanical process involved. When the 
process mechanism is mentioned at all, it is done very 
briefly. In the iumor entries, process mechanism m 
more important than sub-parts and given in more 
detail. Parts are introduced either alter or at the 
same time as their function is defined, and, as a 
consequence, are always defined when presented. 
Furthermore, since the process mechanism follows every 
step of the causal chain, descriptions for the novice 
tend to include more detail about functional 
reformation than descriptions for the expert. We have 
shown how formalization of the strategies allows for 
the development of question-answering systems which 
can tailor their responses to the user, given his level of 
expertise about the domaml2 
ACKNOWLEDGMENTS 
We would like to thank Kathy McKeown and 
Michael Lebowitz for helping in both the research and 
the writing of this paper. This research was supported 
in part by the Defense Advanced Research Projects 
Agency under contract N00039-84-C-0165. 
llDetermmmg the level of expertise of the user is another research problem which we have been studying 
( \[Paris 84\]) 
12Determtmng the level of expertise of the user is another researc~i problem which we have been studying 
( \[Paris 84\]). 
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