SOLUTIONS TO ISSUES DEPEND ON THE KNOWLEDGE REPRESENTATION 
Frederick B. Tho~psoH 
~li£orni~ Institute o£ Technology 
Pasadena, C~,li?orni~ 
In orpQnizing This p~nel, our 
Ch(tirmon, Bob Moore, expressed the view 
thor too often discussion o? Hoturra'l 
l,',nguage occess To dol'o buses has focused 
on whot p~rticulc~r systems c~*n or cQnnot 
do, ro'ther than on underlying issues. He 
Then sd~irr4bly proceeded to orgonize the 
prJnel nr. ound issues r-qther th~n systems. 
In responding, I qttempted to ?rr.iMe my 
~'emr~rk~, on e,ach o? his five issues in r~ 
gener~l woy that would not reflec~ ~y ,wn 
pr4rochiul experience qnd interest, At one 
point I thought th~.~t I h~d s,cceeded quite 
well. Howe,.,er~ offer t~king a cleorer eyed 
view~ it wqs qpparent thor my remarks 
reflec~c;d ~ssumptions obout knowledge 
representotion theft were by no Meons 
univers~ol. This suggests ,a sixth issue 
which I would like ~o r~omin~t,.,: 
Are there r'eolly useful generolizNtions 
~bou~ comput~Jtionr~l linguistic issues 
th<~t c~r,e independer~t of r~ssumptions 
concerning knowledq,.~ r'epre.sentcition? 
I will come back 'to this sixth issue 
q?ter discussing t'i~e ?ire cho-~.,n by our 
Choir~or,. 
I ~s~,e @i : A.q.ctreq~te_.....F.~nc.t i o ns...qnd ~uon.!i.S.~. 
F'irst~ let us csst this issue in o 
~omewhot di.fferent way, Irl m~.sny d~tc, b~se 
~:ituo.1io~s., there ,',r'e closes of 
individuals olI of whose Me~bers shcire the 
~.:oMs ot'~ributes ~and thus, ÷'rum the point 
of view o.f the dr~'t~ bose~ ,ir~ 
.~.ndi~tJ,vuish,~ble. 'Thus there is no need 
~o ~dd ,*II of the~.~. , individuals Qs 
~':.e. prw, o't(~ entities, To use Bob Moore's 
ex,a~ple., i? ,:z DEPARTMENT tile h~ ,.~ ~ield 
Cur NUMPER"OF-EMPL.OYEES~ it strands To 
r'~~,.~on th~L~' the pczr!icul~:~r \[ndividu~.~Is ;~ho 
~c~uolly existed in the v,ar'ious 
dep~r't~tHH~'~ would r~o~ be s~ep,ar,~tely 
r'~pr'e,>~:~,~ed in the. dc~~obose (for uther'wise 
there would be o redund,.~ncy whose 
,..:or1~J'-.:'~.;nc,./ would be h~r'd to police), In 
~u,-'h :~i~u,:~io~s we need the. notion of ~'~ 
",~olleL'ti,~e," homely ~a single dr~tr~ b,ase 
object ~'hot ~,.,l(e~ the; pl~.'~c~, of ra number of 
.ir~divid~.,r, ls end which c,~r~ c,ar'ry their 
cot~on ,~r!'r.Lbul'e~ together with one 
,'~ddition,il item o? in~'ormotion, nomely 
~heir r~umber, Thus ~ DEPARTMENT could 
h~ve ~s o single ~ember su,:h ~ collective 
,.,f employees, indeed it could hove severQl 
such collective MeMbers ond other 
indiuidu~l MeMbers ~s well. The procedure 
thor is c~11ed when onswering "how Mony" 
~nd "nu(~ber of" questions would know the 
dif?eren(-e between subcl~s,~es, indiuidurJl 
(~eMber~ r~nd collective ~embers~ it would 
know to recurse on subclc~sses, ~.~dd one to 
its coun'~ for individual MeMbers ond odd 
the indicoted' number" to its count-for' 
collec:tJve MeMbers. This ~ppe~rs To be 
uni?ied ?r,~ework th,,t will h(1~d\].e ,~11 of 
the c:~s,e~ mentioned in Bob Moore's 
stQtement o? Issue #I. 
Issue '~2: .T,,iM,e, qnci T_e_p._s_e 
I should like to split this issue into 
two, The ?irst sub-issue is the problem of 
hondling continuusly varying phenoMeno> 
~.~uch ra,:, 1he MoveMent of ships~ the 
chqnging of relotiv,., ~zMount,:~ of 
ingredients in che~ic~l reQc~ions~ or "the 
percent completions o9 tnsks, Here it is 
~pp(~rent thr~t eoch instonce will require s 
~peci~lized procedure to hKLnflle 
interpol,~tion. Ships cr~nnot s~il Qcross 
Irjnd~ thus ~n interpolation procedure thor 
produce~ the position of o ship on The 
bdJsis of its points o~' dep~u'tur~, ond 
des'tinotJ, orl will need To know obout the 
c0cAstlines o? conrinents~ Movements to 
cheMJ.c~l equilibriums. ~re not line~r~ t~sk 
coMpletioNs depend on changing personnel 
ossignf~ents. Just rls we coMputotionol 
linguists provide to our syste(,~ u~er the 
(.opobili'¢y to introduce into his dotr~ b~se 
system ~uch notion.'~ ,a~ loc,=rions of" port.~ 
end ship~, etc.> we Must ,also provide ~he 
Met:ins by which he crarl define such 
'.:ontinuously vr~ryir',~ p,ar(~meters r~s 
position in such wqys th~.~t ~tpproprJ.ote 
in~erpo\],',tions c~zn be ~de. by ~he generol 
system in con.junctioN with the p,lrtlculor 
defini'tJon. For" example, 'the user mr~y 
de?ine~ "position o? X" in ter~ of 
('.r~lcu\]:'~%ions, perhops extensive> involvin 9 
~he ,~ctu~.~l 9eo~etr'y of the ~eq~. 
169 
The second sub-issue on which I would 
like. to coMmen~ concerns ~hose c~ses 
where discrete ~ime intervals provide rin 
r.~dequ(l~(~, r, epresentr.~tion o@ "(he time 
aspects relevr, nt to the da'tq bqse. In 
*hese coses~ if` ~he time inf`orf~tion is 
coMplete~ i,e,, rictu(:l st~Ir~lng ~nd ending 
rimes of` rill events ripe recorded in ~he 
d~tQ b,~se, the h~ndling o? time is rrither 
strriightforwrird, However this c~se of"~en 
does not ripply, Consider the ?allowing 
e xQmp\], e. : 
"The Ki~tyhriwk ~rrived in London Monday, 
The Mriru will soil ?ram London Friday. 
Will th~ Kitcyhowk ~nd Hrir'u h~ve been in 
London ~t the s~e time?" 
One is teP~pted ~o ollow the computer 
lo give q response: "Possibly," however 
the introduction of` a three uolued logic 
is Tr'qught with well known d~ngers of" its 
own, A More protrricted response gets in 
the way o~ clnuse \[~bedding; how does one 
hrind\].e~ 
"Will si~ips thrit have been in London 
together sriil together?" 
One rins~er would be: 
"The Ki~i'.vh~.~wk rirrived IriF~t Mondc~y~ 
the Mor, u will soil next Friday, I~ 
they will hrive b~.en there qt the same 
~iMe~ then not rill ships ~hr~t were in 
London together will sriil 1'ogether~ bu~ 
they v:ould be the only exceptions," 
Choosing ~ relev~mt dic~gnosti,: 
t,eessoge~ os obove., is o Mrijor r~nd 
di£?icul't coMputotion,:~l liguis~c issue 
(:~oing w~\],l beyound questions concerning 
t iMe ~lII,J *,ense, 
Issue %3 : _~_~r.ULi.f,,.!..i.\]:Lg ~,p_xo...~u.esx ions 
This i~ a deep~ philosoph\[c,ll 
ques'~io,~. CoMput~,i. onol linguists hove 
pr, ogrw:s~ed beyond tl'w. ,:onsiderqtion o? 
~:~ing\].e ~,.~'ntences, r~nd rire seeking ~o 
,?ollow ~che 'focus of ,\] dirjlogu~. ~ (And 
iden'ti.fy 'the theme o? ~ discourse, This is 
ev~.r}~uqlly ,4n infinite regr'e,~ ultLMritely 
invo\].vi~g cross cul~'ur~l brickgrounds, ~he 
(perh~/ps Mc, chiclvellion> irlt,~.n~ o~ those 
,.,,ha co~,trol ~he u'~e oT o particular 
ctpplicr:~Lon;. ,:It, Dv~: the eng.i.neering 
prob\].ef~, c~ le,~s'r ~ ~he present eta're o£ 
• the c~rt,, i~ :~Lapl~_: whr, t response is ~os~ 
:Jse£u\] "~.o ~'he use.r? Consider kwo possible 
(n~swers ~o ,.'he Following question: 
"Who ,.~on,.'~ges ec~cl~ deportment?" 
Ai: "No single person M~nages ~ll o~ 
the depor~Ments," 
dept. A ~rin~ger A 
Unless ~here were ~n undue number o~" 
dep~rtMents involved~ the second is 
(.Ice, Ply prei~erred~ ?or it ~uf`f`ices "even i? 
the f`irst were intended, I. our own 
experie.,ce, "e~ch" con usefully be 
in'terpreted ,~s coiling ~or ~, l~b~.led list 
,~s onswer in ~l~ost oll coses, The 
diff"icul¢ies of" being t~ore clever ore 
great arid will o~°ten result in 
coMbinqtori(ll explosion, I (~M sur~., for o 
\]ong tJi~e into the future, we will be 
seeking simple solutions that (?.~) ore 
respon,~,ive in Mos~ c(~ses> (b) provide the 
needed inforMr~eion~ even though redund~nt 
Jn SOMe cGse~ rind (c) M~ke c:lerir the 
Misinterpre~rition in the £ew c,~se where 
this rirjses, even though these solutions 
May violrite strict linguistic rinqlysis, 
Issue #4 : ~4e_.,r vi.n~..~.eM~n~ ic~.!_l..y_ CoMp ke X 
In presenting i~his issue Io the prlnel~ 
Bob Moore used the ?ollowlng three 
questions ris ~n example: 
"Is John Jones (, child oF rln HIT 
rll U MIIU ~- ? " 
"Is one o£ John ~ones~s p~rsnts on HIT 
(ll u~)n u.~ 9" 
"Did e.i'~her poren~ o~" /ohn \]ones t~ttend 
HIT?" 
The appqre.t problem is 'the 
po.~sibilit~,, of" Multiple des(-rLptions~ 
o~'ten involving dispor'rite words~ .For, 
getting ~lt dril:t, in ~he datri h~se, In 
(.JeBicjrlillg our" systems) we recognize two 
tru~h~ which ~ppe,~r' to con,flick: (q) the 
v~lue o.F MiniMizing the reduhdrincy o£ 
.LnforMf~tion in the dqt(t b,1~e. (b) the 
necessi-iy o£ non-independent words in the 
vocobulr~ry, In our' own work~ ,~s Mo.~t o? 
you know, we hove stressed the use o? 
definitions c~s u Me~zns of ,'Ich.i.eving o 
synthe~i~ oF '~-hese *.wo princ:iples. I 
recoMMe.d it to you u~ ri v~.r~ o~p.i~ul tool 
in hondlino problems like Bob presents. We 
illustrate how Bob~s excLMpl~; c,.~n be 
hr~ndled : 
"de'fini~ion'child:converse o~" parent 
ve.rb:John ",;it~end"~ HITmJoh. is 
'.-'tud~.t,~ o? HIT 
dei'~inition:~lu~,r-'s'person who hod 
been ~ student" 
170 
The ubove three questions then ore 
?.~n~1 y zed ~s: 
"3"ohn )ones is (converse o? parent) o? a 
person who had been ~ student of HIT?" 
"One of ~ohn /ones's parents is a person 
who had been a student o-t HIT?" 
"W~s ei'ther parent o£ ~ohn ~ones a 
student of HIT?" 
I do not wish to slur' over' the fact 
that ~.= definition Mech~.,nisM ~ust be hifhly 
:sophis~'~coted in i~s handling of f'ree 
variables,, bu~ our ~xperience i~dic~*te.~ 
tha~ ~l'~s can be done quite 
s~tisfac toril y. 
Issue #5: Hu~ti-Fil#._~uer'ie_.s 
This issue has been stated by Bob in 
terms of G tr'~dixional Multiple file de=to 
b,~se s'tructure, This issue h~s its 
coun'ter'p~rt in seM~intic neT data. base 
structures discussed in pr4per,~ on 
k~ow\].edge representation, Since we use 
such q semantic net s~ructure For, our 
data, le't me rephrase the issue in those 
~erMs. In Dab's st~tteMerlt of the issue~ he 
uses tl'~ example of the SHIP file and the 
PORT .File; wl}ere the SHIP f.ile h,~s fields 
-For ho~,~¢ port, departure port and 
destination port. P,~,r'allelLnq his 
exa~p\](:, let us consider ~h~ phrase: 
"London ship", Suppose ~hr.~t (q) there w~s 
ship n,~r~ed London, nnd (b) London was a 
ho~e por~, port of depqrtur~ and 
des'tir~o'~ion~ not necessarily o~" the same 
ship, Then "London ship" is four ways 
,~Mbifuous~ ~e~ning: (i) the ship London~ 
(2) London (ho~e port) ships, (3) l.ondon 
(depr~r~-ur~z par-X) ~hips ~nd (4) London 
(destinq~ion port) ~hips, In this 
for~ul~tion of the probleM~ ~II is easy~ 
insofar ~ the phr~s~; "Londo, ship" is not 
'.iisc~Mbigu~Ted in con'text~ the user is 
informed o? the ~lMbiguous M~lrlincjs (Ind the 
,~ssoci,:~'ted responses. The difficulty 
urises when There ar'~. pos.~ibile 
.i.nterpr,.'<'~'ations ?,~r~her (~field, Fort 
Collins is n,.~.itl')er ,~ port nor ~ ship~ 
however ~.he headqunr'ters of the ABC 
Sllippirt,# CoMpany i~ there un,:l they own 
~everol ships. Wh,~'t ?~r'e we ~o ~e~n by 
"For"t Collins .~hip"? The.~e ~u-e pr'obleM~ 
tha't wer.e ?irs~ ~1'*:acked by Quillicm, and 
f qM not ~ur'e ~'t~(~'t unyone I..~.~ c~dded to hi~ 
!=emii~ol ~r~r~ly':sj.s o£ lhe~, In our own work~ 
we he*re s~uppecJ at "once re~-1oved" 
,.:onnec.'tJons., ,:~ il\].u~r~zTed by the four- 
w~,~y ,~mbiq,)ity ,Ibove. 
Issue ~6: Solution~....tO. Is~q.es_._D~.~.n.. 
As I look back on the abuv~ reMork~ 
t:oncerning Sob's five issues~ it becomes 
~pparent thr~t the u.~efulness of these 
remarks depends on The degree one is aware 
of the knowledge representatLon that 
underlie.s the solution suggested, For 
ex~Mple~ in the case of the last ,Ls~ue,. il ~ 
one only knew about traditional file 
structures~ finding paths theft link fields 
in More Than one file appears all but 
unsolvable, Even if one is accustomed to 
semantic net structures~ the viability of 
finding connective pnth.~ is highl~ 
dependccn~ on the existence of back links 
between attributes and their ,~rgu~en~s and 
values. Adding a definitional capability~ 
other thun simple abbreviqtions ~md 
synonyf4s~ Burns on the way free variables 
ore handled in 9ener~Jl cmd on the 
opporo.tus +'or binding theM) for example, 
in processing the de+'inition: 
"dei~\]nition:are~:length times width" 
when applied ~o q class> say "areas of 
;~hips", how does one ensure ~hat he will 
ob rain : 
"lengTh(i) ~k width(i) 
fop i = I to number of ship~" 
rather Thonl 
"lengTh(i) ~ width(j) 
?or i~j = i to nut.~ber o? ship..=.?" 
It coMe~ down to how variables qre 
MainTained in The underlying knowledge 
represen'tat ion, 
One is £or'ced to conclude ~hat the 
basis ~'or the integrcltion of the syntax 
cu,d ~emonTics o? coMput,~tionr~l linguistic 
systems i~ -ccoMplished wh..n tile 
d¢ci~4ion~ on knowledge r'epre~en~tiun ~r'e 
Made, Di~Jcussions 0£ #ur w:~rLous sotut.En.n 
to ~he J~sues of coMputaTional linguistics 
can Meaningfully ~uke pl<~ce only in terM~ 
uf the,:,~ underlying knowledge 
repr'eser~tot ions. 
171 
