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<Paper uid="E85-1031">
  <Title>INTERPRETING SINGULAR DEFINITE DESCRIPTIONS IN DATABASE QUERIES</Title>
  <Section position="4" start_page="213" end_page="214" type="metho">
    <SectionTitle>
REFERRING TO DATABASE OBJECTS
</SectionTitle>
    <Paragraph position="0"> In a relational database an individual entity is defined by a unique tuple of attributes. The uniqueness of individuals is guaranteed in the database scheme by declaring which attributes constitute the &amp;quot;key&amp;quot; of the relation. The key attributes as it were constitute the &amp;quot;essential&amp;quot; properties of an individual whereas its non-key attributes constitute its &amp;quot;accidental&amp;quot; properties. (The term &amp;quot;individual&amp;quot; is used in a broad sense to denote abstract as well as physical objects, events, acts, situations ...). Philosophically, such properties are said to be &amp;quot;essential&amp;quot; which uniquely characterize an individual in time and space - and remain constant in all &amp;quot;possible worlds&amp;quot;. For example a human being might be essentially characterized by his/her parents, date and time of birth. In everyday discourse, on the other hand, individuals are usually referred 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).</Paragraph>
    <Paragraph position="1"> When interacting with a database querying system a user may well be aware 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 sample is defined by the factory and loca-tion and the date and time it was taken and not by a description such as &amp;quot;the foul smelling sample&amp;quot;. In principle then, the prospective user could be instructed to &amp;quot;use only fully specified descriptions&amp;quot;. This is an unrealistic expectation for two reasons. First, in concrete database designs the key attributes of a relation are not usually chosen to reflect the state of affairs in the real world but rather out of considerations of processing efficiency. Second, the natural inclinition to be concise when interacting in natural language compels the user to use elliptical descriptions, as in the dialogue be- null low : - Where all samples taken from the firm Miller in 1980 analysed ? - Yes.</Paragraph>
    <Paragraph position="2">  -Did the sample taken in October contain any cyanide ? Few users would remember to specify &amp;quot;from the firm Miller&amp;quot; in the follow-up query. A system which wishes to offer a minimum of comfort in use should be able to process &amp;quot;elliptical&amp;quot; descriptions which can be made unique by supplementing information from the preceding context.</Paragraph>
    <Paragraph position="3"> So far we have assumed that in principle all entities a user wishes to refer 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, &amp;quot;the sample from Miller that contained 250 mg of arsenic&amp;quot;. Such descriptions could be distinguished from the former by the fact that they contain some non-key attributes which the user claims happen to evaluate to a unique entity in a particular state of the database.</Paragraph>
    <Paragraph position="4"> From the point of view of establishing the uniqueness of singular definite descriptions, one might distinguish the following four types : (i) intrinsically functional descriptions null (ii) extrinsically functional descriptions null (iii) incomplete extrinsically functional descriptions (iv) non-functional or reference establishlng descriptions Descriptions in category (i) are functional by virtue of the linguistic expression used. These include superlatives such as the highest salary,, exprestions denoting aggregate functions such as the average, the sum ... and expressions with nominal modifiers such as the colour red and the number 13. Descriptions in category (ii) are functional by virtue of the state of the world (reflected in the database scheme and the integrity 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 instances of category (ii) which can be made functional by searching contextual information or by requesting such information from the user. Descriptions in category (iv) are sometimes called &amp;quot;reference establishing&amp;quot; as the 8peclfied properties do not guarantee the uniqueness of the description but the speaker maintains the description denotes uniquely and expects the hearer to accept  this assumption.</Paragraph>
    <Paragraph position="5"> In order to process descriptions efficiently a natural language processor should be able to recognize the type of a description. Intrinsically functional descriptions may be evaluated immediately in the database. For extrinsically functional descriptions the database scheme and the integrity constraints could indicate whether a given description 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 descriptions 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.</Paragraph>
    <Paragraph position="6"> Obviously, the proposals are only very tentative and require more thorough research. However, the bring us to consider the auestion of checking the uniqueness claim implicit in the use of singular the.</Paragraph>
    <Paragraph position="7"> A natural language query to a relational database is usually translated into a query language based on the relationsl calculus and the singular definite article is represented by the existential quantifier. For example, the query - Who is the president of the U.S.</Paragraph>
    <Paragraph position="8"> married to might be presented in a query language bssed on the domain relational calculus</Paragraph>
    <Paragraph position="10"> 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 representations. Thus, the distinction between restrictive and non-restrictive modifiers is ignored. (Of course the representation of non-restrictive modifiers introduces the additional problems of how to process surplus information).</Paragraph>
    <Paragraph position="11"> The following major proposals for the logical form of the singular definite article have been made : contextual elimination, 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 description, i.e. a description has no reference out of context. Russell's inclu-Sion of the uniqueness postulate as a truth condition for the proposition implies that the sentence is false when the uniqueness claim fails. If the is treated as a description operator creating a singular term, the description may receive a denotation out of context.</Paragraph>
    <Paragraph position="12"> 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 advocated in Moore 1981 because it allows indication of scope differences. In the context of query evaluation it would seem more user-cooperative to treat propositions containing descriptions which do not evaluate to a unique referent as lacking truth value ; thus, the uniquemess claim might be viewed as a &amp;quot;semantic presuppostion&amp;quot;. Under the assumption that it is desirable for reasons of communicative adequacy to represent the relational claim in queries, it should be investigated how query languages based on the relational calculus could be augmented by a special quantifier or operator, given that the contextual elimination approach would create an excessive processing overhead.</Paragraph>
  </Section>
  <Section position="5" start_page="214" end_page="215" type="metho">
    <SectionTitle>
ON THE PRAGMATICS OF REFER/LING E~!~RES -
SIONS
</SectionTitle>
    <Paragraph position="0"> In natural discourse situations a speaker choses a description which will enable the listener to identify the speaker has in mind. In some contexts, however, &amp;quot;identification&amp;quot; is not to be interpreted in terms of the hearer retrieving some memory entity having the properties of the description. For example, a hearer may have been told : &amp;quot;the president of Zalre will be visiting France next week&amp;quot;. 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 referent or storing the description. (This is not the case in all contexts. For example, the statement &amp;quot;the woman who broke her leg is recovering&amp;quot; assumes previous knowledge of the referent, whereas the description the president of Zaire presumably only presuposes the previous knowledge that Zaire is a country and that countries may be governed by a president. (This aspect of the pragmatics of definite descriptions would be an interesting research topic, which to our knowledge has not been investigated)  However, the speaker does not always leave the interpretation strategy up to the hearer but sometimes requires the hearer to identify the specific individual s/he has in mind, whereas in other contexts it may be the speaker's intention not to denote a specific individual but rather that the description be applied to the semantic referent. This is roughly the distinction made by &amp;quot;Donnellan between the &amp;quot;referential&amp;quot; and the &amp;quot;attributive&amp;quot; uses of the singular definite article.</Paragraph>
    <Paragraph position="1"> Do the above observations about descriptions in statements eaually aoply to questions and is the referential/attrlbutive distinction relevant in the context of database querying ? To answer this question comprehensively involves in the last resort epistimological considerations.</Paragraph>
    <Paragraph position="2"> 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 represents a true proposition, after the description has received an extensional evaluation, ie colonel Mobutu. The extensional approach to semantic evaluation is the one adopted in database querying. This strategy would seem appropriate in most cases. Suppose, however, the user asks the query &amp;quot;Can the nresident of the U.S. veto the Senate?&amp;quot;. This description is not intended referentially (ie about Ronald Reagan in 1985) but attributively. It might be objected that the description in this context rather denotes a generic concept and that conventional database systems are not set up to answer such aueries. Nevertheless, when a description has been extensionally evaluated the description itself should be retained for the subsequent resolution of anaphoric expressions. For example, in the following dialogue :  - Did the president of the U.S.</Paragraph>
    <Paragraph position="3"> visit France in 1982 ? - No.</Paragraph>
    <Paragraph position="4"> - Did he visit Germany in 1979 ?  Substitution of &amp;quot;Ronald Reagan&amp;quot; in the second query would result in a wrong answer. (Different interpretation modes for anaphoric descriptions have been investigated more thoroughly in Grosz et. al. 1983).</Paragraph>
  </Section>
  <Section position="6" start_page="215" end_page="215" type="metho">
    <SectionTitle>
DISCOURSE REFERENTS IN DATABASE QUERIES
</SectionTitle>
    <Paragraph position="0"> In the preceding section it was seen that a truth-functional evaluation of queries presupposes an extensional evaluation of descriptions in the database. In natural discourse situations the referent of a description may be another description which appeared previously in the discourse, rather than an entity in the real world. This previously mentioned entity may be called a &amp;quot;discourse referent&amp;quot; a term introduced by Karttunen to explain certain phenomena of referential indexing for definite descriptions. According to Karttunen 68~a a discourse referent is &amp;quot;an entity that once it has been established - can be referred to by a pronoun or revived by a definite description&amp;quot; and is not to be equated with either &amp;quot;the individual the speaker has in mind&amp;quot; nor with &amp;quot;the thing in the real world&amp;quot;. Yer example, the assertion ($I) Jones took a sample from the firm Miller establishes a discourse entity which may be revived by &amp;quot;the sample that Jones took from the firm Miller&amp;quot;. Discourse 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).</Paragraph>
    <Paragraph position="1"> Adopting the logical formalism for describing 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 description. null How does the notion of &amp;quot;discourse referent&amp;quot; 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 ? Obviously, the description &amp;quot;the sample Jones took from the firm Miller&amp;quot; can only be used subsequently if the answer to ($2) is positive. It might be posited hence that the reply</Paragraph>
  </Section>
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