INTERPRETING SINGULAR DEFINITE DESCRIPTIONS IN DATABASE QUERIES 
Genevieve Berry-Rogghe 
Department of Computer and Information Science 
Temple University 
Philadelphia, PA 19122 
USA 
ABSTRACT 
The paper examines some of the cha- 
racteristic features of natural langua- 
ge interaction with a database system 
and its implications for the processing 
of singular definite descriptions. Some 
proposals are made for assessing the 
uniqueness claim of the singular defini- 
te article in the context of retrieval 
from a relational database. Other stan- 
dard assumptions such as the extensio- 
nal evaluation and referent evaluation 
exclusively in the database - rather 
than within the discourse model - are 
critically examined. 
INTRODUCTION 
A comprehensive treatment of the phe- 
nomenon of singular definite description 
in natural language processing constitu- 
tes a research program par excellence in 
the field of cognitive science. Not only 
does it involve the various cognitive 
disciplines but also the integration of 
the traditional levels of analysis, na- 
mely the syntactic, semantic and pragma- 
tic levels as well as including a "per- 
formance" or processing level dealing 
with mechanisms for memory managment of 
referring expressions. Linguistic theo- 
ries initially attempted to account for 
the syntactic conditions of well-formed- 
ness governing the introduction of sin- 
~ular definite nounphrases in sentences 
by postulating co-referentiality with a 
previously occurring indefinite noun- 
phrase having the same referential in- 
dex. But it became clear that the postu- 
lated requirements of co-referentiality 
could only be adequately stated by means 
of an extended notion of "discourse re- 
ferent" (see Karttunen 1968 b). 
Logicians and philosophers of language 
since Russell have studied problems of 
reference and of the logical form of re- 
ferring expressions occurring in various 
contexts (for a selection, see Linsky 
1971). But it was pointed out in Donnel- 
lan 1966 that a strictly truthfunctional 
analysis of singular definite expres- 
sions may in certain situations evaluate 
to a referent which was not intended by 
the speaker. Accounting for the inten- 
tions of the speaker introduces the prag- 
matic point of view of referring as a 
speech act (see Searle 1966). How the 
speaker proceeds in describing an object 
s/he has in mind so that it may be cor- 
rectly identified by the hearer and how 
the hearer perceives the intentions of 
the speaker to accordingly process des- 
criptions has been the object of psycho- 
logically oriented research in the area 
of definite reference (e.g. Clark/Mar- 
shall 1981 and Ortony-Anderson 1977). In 
Artificial Intelligence, research on de- 
finite descriptions has mainly proposed 
computational models to resolve anapho- 
ric reference by postu21ating certain in- 
ference mechanisms (e.g. Charnlak 1972 
and Rieger 1974) or mechanisms for detec- 
ting and managing dialogue focus (e.g. 
Grosz 1981 and Sidner 1979). 
Considering practical applications in 
the computer processing of natural lan- 
guage it may be said that next to none 
of this large body of research has been 
incorporated. Most natural language 
front-ends to a standard database system 
support none or very primitive reference 
resolution and treat the singular defini- 
te article as an existential quantifier. 
This state of affairs has frequently been 
motivated by the objection that most of 
the aforementioned research is not yet 
able to meet the challenge of a computa- 
tionally efficient solution. It is hoped 
that such objections, though justified, 
\[see for example Berwick 1985) will dimi- 
nish in the course of time. More telling 
are objections relating to the nature of 
the natural language interaction with a 
database system which is alleged to con- 
stitute a restricted discourse environ- 
ment not displaying the more sophistica- 
ted features of natural dialogue. The 
present paper critically examines some 
characteristics of such interactions with 
respect to the processing of definite 
descriptions and investigates to what ex- 
tent the research findings aluded to abo- 
ve ought to be incorporated. The paper is 
intended to give an overview of the pro- 
213 
blem domain rather than to offer concre- 
te solutions ; in fact its aim is to 
point out areas where fruitful research 
is still outstanding. 
REFERRING TO DATABASE OBJECTS 
In a relational database an indivi- 
dual entity is defined by a unique tup- 
le of attributes. The uniqueness of in- 
dividuals is guaranteed in the database 
scheme by declaring which attributes 
constitute the "key" of the relation. 
The key attributes as it were constitu- 
te the "essential" properties of an in- 
dividual whereas its non-key attributes 
constitute its "accidental" properties. 
(The term "individual" is used in a 
broad sense to denote abstract as well 
as physical objects, events, acts, situ- 
ations ...). Philosophically, such pro- 
perties are said to be "essential" which 
uniquely characterize an individual in 
time and space - and remain constant in 
all "possible worlds". For example a hu- 
man being might be essentially characte- 
rized by his/her parents, date and time 
of birth. In everyday discourse, on the 
other hand, individuals are usually re- 
ferred to by a particular description 
which enables the hearer to identify the 
entity and which is chosen on the basis 
of assumptions about shared knowledge 
between the discourse participants. (See 
Clark/Marshall 1981 for a more detailed 
account of these assumptions). 
When interacting with a database 
querying system a user may well be awa- 
re of the fact that s/he does not share 
any previous experience with the system 
and that it is hence appropriate to 
characterize objects by their defining 
properties in the real world, iea sam- 
ple is defined by the factory and loca- 
tion and the date and time it was taken 
and not by a description such as "the 
foul smelling sample". In principle 
then, the prospective user could be in- 
structed to "use only fully specified 
descriptions". This is an unrealistic 
expectation for two reasons. First, in 
concrete database designs the key attri- 
butes of a relation are not usually cho- 
sen to reflect the state of affairs in 
the real world but rather out of consi- 
derations of processing efficiency. Se- 
cond, the natural inclinition to be con- 
cise when interacting in natural lan- 
guage compels the user to use ellipti- 
cal descriptions, as in the dialogue be- 
low : 
- Where all samples taken from the 
firm Miller in 1980 analysed ? 
- Yes. 
-Did the sample taken in October 
contain any cyanide ? 
Few users would remember to specify "from 
the firm Miller" in the follow-up query. 
A system which wishes to offer a minimum 
of comfort in use should be able to pro- 
cess "elliptical" descriptions which can 
be made unique by supplementing informa- 
tion from the preceding context. 
So far we have assumed that in prin- 
ciple all entities a user wishes to re- 
fer to can be characterlsed by a number 
of essential properties. In reality the 
user often does not know the values for 
the essential attributes and hence has 
to use another description to refer to 
the entity ; for example, "the sample 
from Miller that contained 250 mg of ar- 
senic". Such descriptions could be dis- 
tinguished from the former by the fact 
that they contain some non-key attribu- 
tes which the user claims happen to eva- 
luate to a unique entity in a particular 
state of the database. 
From the point of view of establis- 
hing the uniqueness of singular defini- 
te descriptions, one might distinguish 
the following four types : 
(i) intrinsically functional descrip- 
tions 
(ii) extrinsically functional descrip- 
tions 
(iii) incomplete extrinsically functio- 
nal descriptions (iv) 
non-functional or reference esta- 
blishlng descriptions 
Descriptions in category (i) are fun- 
ctional by virtue of the linguistic ex- 
pression used. These include superlati- 
ves such as the highest salary,, expres- 
tions denoting aggregate functions such 
as the average, the sum ... and expres- 
sions with nominal modifiers such as the 
colour red and the number 13. Descrip- 
tions in category (ii) are functional by 
virtue of the state of the world (reflec- 
ted in the database scheme and the inte- 
grity constraints). The president of the 
United States in I~8~, the sample from 
~he flrm Miller taken on 13.10.80 and 
the salary Of G.B. Jones are examples of 
this catagory. Descriptions in category 
(lii) are incompletely specified instan- 
ces of category (ii) which can be made 
functional by searching contextual in- 
formation or by requesting such informa- 
tion from the user. Descriptions in ca- 
tegory (iv) are sometimes called "refe- 
rence establishing" as the 8peclfied 
properties do not guarantee the unique- 
ness of the description but the speaker 
maintains the description denotes uni- 
quely and expects the hearer to accept 
214 
this assumption. 
In order to process descriptions ef- 
ficiently a natural language processor 
should be able to recognize the type of 
a description. Intrinsically functional 
descriptions may be evaluated immediate- 
ly in the database. For extrinsically 
functional descriptions the database 
scheme and the integrity constraints 
could indicate whether a given descrip- 
tion is fully specified. In case the 
description contains some but not all 
key attributes and it does not contain 
any non-key attributes it would seem to 
belong to category (iii) and in case it 
contsins any non-key attributes it would 
appear to belong to category (iv). For 
cases of incomplete functional descrip- 
tions complementation procedures should 
be invoked, whereas the non-functional 
descriptions must be evaluated and an 
error message should be sent in case the 
description does not denote uniquely. 
Obviously, the proposals are only very 
tentative and require more thorough re- 
search. However, the bring us to consi- 
der the auestion of checking the unique- 
ness claim implicit in the use of singu- 
lar the. 
A natural language query to a rela- 
tional database is usually translated 
into a query language based on the rela- 
tionsl calculus and the singular defini- 
te article is represented by the exis- 
tential quantifier. For example, the 
query 
- Who is the president of the U.S. 
married to 
might be presented in a query language 
bssed on the domain relational calculus 
8s 
I c x = x, COUNTRY = /3 PRES (PERSON 
'USA ' )/~ 
MARRIED-TO (PERSON =~ x, PER- 
SON = C)} 
For a system to ignore the uniqueness 
claim of the singular definite article 
is st best uncooperative and at worst 
may lead to semantically incorrect re- 
presentations. Thus, the distinction be- 
tween restrictive and non-restrictive 
modifiers is ignored. (Of course the re- 
presentation of non-restrictive modifiers 
introduces the additional problems of 
how to process surplus information). 
The following major proposals for the 
logical form of the singular definite 
article have been made : contextual eli- 
mination, a description operator and a 
special quantifier, Russell's proposal, 
namely Q(the x Px)a-*~ x Px A (W y Py--~y= 
x)/% Qx contextually eliminates the des- 
cription, i.e. a description has no re- 
ference out of context. Russell's inclu- 
Sion of the uniqueness postulate as a 
truth condition for the proposition im- 
plies that the sentence is false when 
the uniqueness claim fails. If the is 
treated as a description operator crea- 
ting a singular term, the description 
may receive a denotation out of context. 
When the description has no referent, 
the proposition contains an undefined 
argument and on some interpretations 
lacks truth value. The treatment of the 
as a quantifier which takes a pair of 
predicates to form a sentence was advo- 
cated in Moore 1981 because it allows 
indication of scope differences. In the 
context of query evaluation it would 
seem more user-cooperative to treat pro- 
positions containing descriptions which 
do not evaluate to a unique referent as 
lacking truth value ; thus, the unique- 
mess claim might be viewed as a "seman- 
tic presuppostion". Under the assumption 
that it is desirable for reasons of com- 
municative adequacy to represent the 
relational claim in queries, it should 
be investigated how query languages ba- 
sed on the relational calculus could be 
augmented by a special quantifier or 
operator, given that the contextual eli- 
mination approach would create an exces- 
sive processing overhead. 
ON THE PRAGMATICS OF REFER/LING E~!~RES - 
SIONS 
In natural discourse situations a 
speaker choses a description which will 
enable the listener to identify the spe- 
aker has in mind. In some contexts, ho- 
wever, "identification" is not to be in- 
terpreted in terms of the hearer retrie- 
ving some memory entity having the pro- 
perties of the description. For example, 
a hearer may have been told : "the pre- 
sident of Zalre will be visiting France 
next week". Storing this proposition 
does not require finding a referent for 
the description the president of Z aire 
- although s/he may do so depending on 
the hearer's world knowledge. It would 
appear that when processing statements 
containing descriptions, the hearer has 
the choice of either resolving the re- 
ferent or storing the description. (This 
is not the case in all contexts. For ex- 
ample, the statement "the woman who bro- 
ke her leg is recovering" assumes pre- 
vious knowledge of the referent, where- 
as the description the president of Za- 
ire presumably only presuposes the pre- 
vious knowledge that Zaire is a country 
and that countries may be governed by 
a president. (This aspect of the prag- 
matics of definite descriptions would be 
an interesting research topic, which to 
our knowledge has not been investigated) 
215 
However, the speaker does not always 
leave the interpretation strategy up to 
the hearer but sometimes requires the 
hearer to identify the specific indivi- 
dual s/he has in mind, whereas in other 
contexts it may be the speaker's inten- 
tion not to denote a specific indivi- 
dual but rather that the description be 
applied to the semantic referent. This 
is roughly the distinction made by "Do- 
nnellan between the "referential" and 
the "attributive" uses of the singular 
definite article. 
Do the above observations about des- 
criptions in statements eaually aoply 
to questions and is the referential/at- 
trlbutive distinction relevant in the 
context of database querying ? To ans- 
wer this question comprehensively in- 
volves in the last resort epistimologi- 
cal considerations. 
The question Will the president of Znire 
be visiting France might be answered 
positively by someone who happened to 
have read this news in the paper. Truth 
-functionally, however, the question 
can only receive a positive answer in 
case the corresponding statement repre- 
sents a true proposition, after the 
description has received an extensional 
evaluation, ie colonel Mobutu. The ex- 
tensional approach to semantic evalu- 
ation is the one adopted in database 
querying. This strategy would seem ap- 
propriate in most cases. Suppose, how- 
ever, the user asks the query "Can the 
nresident of the U.S. veto the Senate?". 
This description is not intended refe- 
rentially (ie about Ronald Reagan in 
1985) but attributively. It might be 
objected that the description in this 
context rather denotes a generic con- 
cept and that conventional database 
systems are not set up to answer such 
aueries. Nevertheless, when a descrip- 
tion has been extensionally evaluated 
the description itself should be retai- 
ned for the subsequent resolution of 
anaphoric expressions. For example, in 
the following dialogue : 
- Did the president of the U.S. 
visit France in 1982 ? 
- No. 
- Did he visit Germany in 1979 ? 
Substitution of "Ronald Reagan" in the 
second query would result in a wrong 
answer. (Different interpretation mo- 
des for anaphoric descriptions have 
been investigated more thoroughly in 
Grosz et. al. 1983). 
DISCOURSE REFERENTS IN DATABASE QUERIES 
In the preceding section it was seen 
that a truth-functional evaluation of 
queries presupposes an extensional eva- 
luation of descriptions in the database. 
In natural discourse situations the re- 
ferent of a description may be another 
description which appeared previously in 
the discourse, rather than an entity in 
the real world. This previously mentio- 
ned entity may be called a "discourse 
referent" a term introduced by Karttun- 
en to explain certain phenomena of re- 
ferential indexing for definite descrip- 
tions. According to Karttunen 68~a a 
discourse referent is "an entity that - 
once it has been established - can be 
referred to by a pronoun or revived by 
a definite description" and is not to be 
equated with either "the individual the 
speaker has in mind" nor with "the thing 
in the real world". Yer example, the 
assertion 
($I) Jones took a sample from the 
firm Miller 
establishes a discourse entity which 
may be revived by "the sample that Jo- 
nes took from the firm Miller". Discour- 
se referents in the strict sense are 
introduced in the discourse by means of 
an indefinite description. (The notion 
has been extended in Karttunen 68 b). 
Adopting the logical formalism for des- 
cribing discourse referents proposed in 
Webber 1978 this discourse referent 
could be described as : 
Lx : SAMPLE (x)/k TOOK (Jones,x) 
/k ORIGIN (x, Miller)A EVOKE (x, sl) 
A proposition mentioning the sentence 
where the indefinite description was 
introduced establishes the contextual 
uniqueness of the singular definite des- 
cription. 
How does the notion of "discourse 
referent" as explained above operate in 
questions ? For example, does the query 
($2) Did Jones take a sample from 
the firm Miller ? 
establish a discourse referent ? Ob- 
viously, the description "the sample 
Jones took from the firm Miller" can 
only be used subsequently if the ans- 
wer to ($2) is positive. It might be 
posited hence that the reply 
($3) Yes 
implies the statement "Jones took a 
sample from the firm Miller" and that 
hance the description of the discourse 
referent would contain the proposition 
EVOKE (x, S~). 
216 
A system which behaves like a natu- 
ral discourse partner should store the 
description of the discourse referent 
(together with a pointer to its referen- 
tial index which was retrieved on ans- 
wering $2). If the user should in the 
subsequent discourse - no matter how 
many sentences intervene - refer to 
"the sample Jones took from Miller" the 
system should not reject this descrip- 
tion as being incompletely specified. 
If the answer to ($2) had been ne- 
gative, no discourse referent would 
have been established. Can one infer 
from this example the general rule 
that negatively answered questions can- 
not establish a discourse referent ? 
Consider the following interaction : 
(S4) Did the graduate admissions 
committee hold a meeting today? 
(s~) ~o. 
($6) Was the meeting postponed ? 
Can the expression "the meeting" in ($6) 
be construed as an abbreviation for 
"the meeting of the graduate admissions 
committee which was not held yesterday" 
or is it simply an abbreviation for 
"the meeting of the graduate admissions 
committee" ? The difference between 
($2) and ($4) can perhaps be accounted 
for by the difference between the non- 
-s~ecific use of the indefinite article 
in ($2) and the specific use in ($4). 
In the specific use the relative clause 
derived from the predicate in the ori- 
ginal question, ie that was held yester- 
day, should be understood in a non-re- 
strictive sense and is hence not an es- 
sential part in the description of the 
discourse referent. Further research 
into the behaviour of indefinites in 
negative and interrogative contexts is 
is again called for. 
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