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<?xml version="1.0" standalone="yes"?> <Paper uid="E83-1025"> <Title>References</Title> <Section position="3" start_page="146" end_page="149" type="metho"> <SectionTitle> 3 Interplay of syntax, semantics, and pragmatics in </SectionTitle> <Paragraph position="0"> pronominalization The process of pronominalization is governed by rules involving morphological, syntactic, semantic, and pragmatic criteria. These rules are discussed and illustrated with examples drawn from the context of querying a geographical database. Then a procedure is outlined which uses these rules and applies them in the following order: First morphological criteria are checked, if they fail no further tests are required.</Paragraph> <Paragraph position="1"> Then syntactic (or configurational) criteria are tested. Again, if they fail, no further tests are necessary.</Paragraph> <Paragraph position="2"> Next semantic criteria are applied, and if they do not fail, the pragmatic criteria have to be tested. If more than one candidate remains, the use of the pronoun was pragmatically inappropriate and must be noted as such.</Paragraph> <Section position="1" start_page="146" end_page="148" type="sub_section"> <SectionTitle> 3.1 Strict factors determining the admissibility of anaphora </SectionTitle> <Paragraph position="0"> Morphological criteria concern the agreement of gender and number. Complications come in, when coordinated noun phrases occur, e.g.</Paragraph> <Paragraph position="1"> (2) John and Bill went to Pisa. They delivered a paper.</Paragraph> <Paragraph position="2"> (3) *John and Bill went to Pisa. He delivered a paper. null (4) John and Sue went to Pisa. He delivered a paper. null (5) *John or Bill went to Pisa. They delivered a paper.</Paragraph> <Paragraph position="3"> (6) *John or Bill went to Pisa. He delivered a paper. null (7) Neither John nor Bill went to Pisa. They went to Rome.</Paragraph> <Paragraph position="4"> (8) *Either John or Bill did not go to Pisa. He went to Rome.</Paragraph> <Paragraph position="5"> The starred examples contain inappropriate uses of pronouns. With and-coordination, reference to the complete NP is possible with a plural pronoun. When the members of the coordination are distinct in gender and/or number, reference to them is possible with the corresponding pronouns. Clearly, the same observations hold for interrogative sentences.</Paragraph> <Paragraph position="6"> Syntactic criteria operate only within the boundaries of a sentence, outside they are useless. The configurational critp.ria stemming from DRT however work independent of sentence boundaries. Disjoint reference The rule of &quot;disjoint reference&quot; according to Reinhart (1983) goes back to Chomsky and has been refined by Lasnik (1976) and Reinhart (1983). It is able to handle a variety of well-known cases, such as (9) When did it join the UN? (10) Which countries that import it, produce petrol? (11) *Does it entertain diplomatic relations with Spain's neighbor? (In the starred example, the use of &quot;it&quot; is inappropriate, if it is to be coreferential with &quot;Spain&quot;.) Rather than using c-command to formulate this criterion, which is elegant but too strict in some cases (as noted by Reinhart herself and Bolinger (1979), we have chosen an admittedly less elegant, but hopefully reliable, approach to disjoint reference, in that we specify the concrete syntactic configurations where disjoint reference holds. We do not rely here on the syntactic framework of USL grammar, but use more or less traditionally known terminology for expressing our rules. We need the terms &quot;clause&quot;, &quot;phrase&quot;, &quot;matrix&quot;, &quot;embedding&quot;, and &quot;level&quot;. These can be made explicit, when a suitable syntactic framework is chosen.</Paragraph> <Paragraph position="7"> Now we can formulate our disjoint reference rule and some of its less obvious consequences. CI. The referent of a personal pronoun can never be within the same clause at the same phrase level. (Note that this rule does not hold for possessive pronouns,) C1 has a number of consequences which we now list: Cla. The (implicit) subject of an infinitve clause can never be referent of a personal pronoun in that clause (12) Does the EC want to dissolve it? Clb. Nouns common to coordinate clauses cannot be referred to from within these coordinate clauses (13) Which country borders it and Spain? Clc. Noun complements of nouns in the same clause can never be referred to.</Paragraph> <Paragraph position="8"> (14) Does it border Spain's neighbors? The following rules have to do with phrases and clauses modifying a noun. They too can be regarded as consequences of C1.</Paragraph> <Paragraph position="9"> C2. Head noun of a phrase or clause can never be referent of a personal pronoun in that phrase or clause C2a. Head noun of participial phrase (15) a country exporting petrol to it C2b. Head noun of that-clause (16) the truth is that it follows from A. C2c. Head noun of relative clause (17) the country it exports petrol to The following two rules deal with kataphoric pronominalization (sometimes called backward pronominalization). null C3a. Kataphora into a more deeply embedded clause is impossible (18) Did it export a product that Spain produces? C3b. Kataphora into a succeeding coordinate clause is impossible (19) Who did not belong to it but left the UN? The accessibility relation on DRSs C4. Only those discourse referents in the accessibility relation defined in sec. 2.2 are available as referents to a pronoun.</Paragraph> <Paragraph position="10"> Widely used is the criterion of semantic compatibility. It is usually implemented via &quot;semantic features&quot;. In the USL framework we can derive this information from relation schemata. We state the criterion as follows: 31. If s is a sentence containing a pronoun p and c a full noun phrase in the context of p. If p is substituted by c in s to yield s' and s' is not semantically anomalous, i.e. does not imply a contradiction, then c is semantically compatible with s and is hence a semantically possible candidate for the reference of p.</Paragraph> <Paragraph position="11"> (20) What is the capital of Austria? - Vienna. What does it export? If it is assumed that only countries but not capitals export goods, then the only semantically possible referent for &quot;it&quot; is Austria.</Paragraph> <Paragraph position="12"> S2. Non-referentially introduced nouns cannot be antecedents of pronouns.</Paragraph> <Paragraph position="13"> (21) Which countries does Italy have trade with? How large is it? Since &quot;trade&quot; is used non-referentially, it cannot be antecedent of &quot;it&quot;. Unfortunately, in many cases where this criterion could apply, there is an ambiguity between referential and non-referential use.</Paragraph> <Paragraph position="14"> Apart from the type of semantic compatibility covered by rule S1, more complex semantic properties are used to determine the referent of a pronoun. The &quot;task structures&quot; described by Grosz (1977) illustrate this fact. We hence formulate the rule $3. The properties of and relationships between predicates determine pronorninalizability. For an illustration of its effect, consider the following query: (22) What country is its neighbor? The irreflexivity of the neighbor-relation entails that &quot;its&quot; cannot be bound by &quot;what country&quot; in this case, but has to refer to something mentioned in the previous context.</Paragraph> <Paragraph position="15"> Given a subject domain, one can analyze the properties of the relations and the relationships between them and so build a basis for deciding pronoun reference on semantic grounds. In the framework of the USL system, information on the properties of relations is available in terms of &quot;functional dependencies&quot; given in the database schema or as integrity constraints.</Paragraph> </Section> <Section position="2" start_page="148" end_page="149" type="sub_section"> <SectionTitle> 3.2 Pragmatic criteria </SectionTitle> <Paragraph position="0"> The generation of discourse is controlled by two factors: communicative intentions and mutual knowledge. In the context of database interaction, we can assume that the communicative intentions of a user are simply to obtain factual answers to factual questions. His intentions are expressed either by single queries or by sequences of queries, depending on how complex these intentions are or how closely they correspond to the information in the database. As will be shown below, in many cases the system will not have a chance to determine whether a given query is a &quot;one-shot query&quot;, or whether it is part of a sequence of queries with a common &quot;theme&quot;. For the resolution of pronouns, this means that the system should rather ask the user back than make wild guesses on what might be the most &quot;plausible&quot; referent. This is of course not possible when running text is analyzed in a &quot;batch mode&quot;, and no user is there to be asked for clarification.</Paragraph> <Paragraph position="1"> Mutual knowledge (see e.g. Clark and Marshall (1981) for a discussion) determines the rules for introducing and referencing individuals in the discourse. In the context of database interaction we assume the mutual knowledge to consist initially of: - the set of proper names in the database, - the predicates whose extensions are in the database, null -the &quot;common sense&quot; relationships between and properties of these predicates.</Paragraph> <Paragraph position="2"> It will be part of the design of a database to establish what these &quot;common sense&quot; relationships and properties are,.e.g, whether it is generally known to the user community, whether &quot;capital&quot; expresses a one-one relation. Each question-answer pair occurring in the discourse is added to the stock of mutual knowledge.</Paragraph> <Paragraph position="3"> It is a pragmatic principle of pronominalization that only mutual knowledge may be used to determine the referent of a pronoun on semantic grounds, and hence it may be legal to use the same sentence containing a pronoun where earlier in the discourse it was illegal, because the mutual knowledge has increased in the meantime.</Paragraph> <Paragraph position="4"> 3.2.1 A first attempt using preference rules What the topic of a discourse is, which of the entities mentioned in it are in focus, is reflected in the syntactic structure of sentences. This has been observed for a long time. It has also often been observed that discourse topic and focus have an effect on pronominalization where morphological, configurational, and semantic rules fail to determine a single Candidate for reference. However, it has not been possible yet to formulate precise rules explaining this phenomenon. We have the impression that such rules cannot be absolutely strict rules, but are of a preferential nature. We have developed a set of such rules and tested them against a corpus of text containing some 600 pronoun occurrences, and have found them to work remarkably well. Similar tests (with a similar set of rules) have been conducted by Hofmann (1976).</Paragraph> <Paragraph position="5"> In the sequel we formulate and discuss our list of rules. Their ordering corresponds to the order in which they have to be applied.</Paragraph> <Paragraph position="6"> P1 (principle of proximity). Noun phrases within the sentence containing the pronoun are preferred over noun phrases in previous or succeeding sentences. null Consider the sequence (23) What country joined the EC after 1980? Greece.</Paragraph> <Paragraph position="7"> (24) What country consumes the wine it produces? One could argue that &quot;Greece&quot; is just as probably the intended referent of &quot;it&quot; in this case as the bound interpretation and that hence the use of &quot;it&quot; should be rejected as inappropriate. However, there is no way to avoid the &quot;it&quot;, if the bound variable interpretation is intended, and one can use this as a ground to rule out the interpretation where &quot;it&quot; refers to &quot;Greece&quot;.</Paragraph> <Paragraph position="8"> Pla. Noun phrases in sentences before the sentence containing the pronoun are preferred over noun phrases in more distant sentences.</Paragraph> <Paragraph position="9"> This criterion is very important to limit the search for possible discourse referents.</Paragraph> <Paragraph position="10"> P2. Pronouns are preferred over full noun phrases.</Paragraph> <Paragraph position="11"> This rule is found in many systems dealing with anaphora. One can motivate it by saying that pronominalization establishes an entity as a theme which is then maintained until the chain of pronouns is broken by a sentence not containing a suitable pronoun. For an example consider: P3. Noun ~hrases in a matrix clause or phrase are preferred over noun phrases in embedded clauses or phrases.</Paragraph> <Paragraph position="12"> P3a. Noun phrases in a matrix clause are preferred over noun phrases in embedde~ clauses.</Paragraph> <Paragraph position="13"> Example: (28) What country imports a product that Spain produces? - Denmark.</Paragraph> <Paragraph position="14"> (29) What does it export? Here &quot;it&quot; has to refer to the individual satisfying &quot;what country&quot;, not to &quot;Spain&quot; which occurs in an embedded clause.</Paragraph> <Paragraph position="15"> P3b. Head nouns are preferred over noun complements. null Example: (30) What is the capital of Austria? - Vienna.</Paragraph> <Paragraph position="16"> (31) What is its population? &quot;Vienna&quot;, not &quot;Austria&quot; becomes the referent of &quot;its&quot;, and the argument is analogous to that for P3a.</Paragraph> <Paragraph position="17"> P4. Subject noun phrases are preferred over non-subject noun phrases.</Paragraph> <Paragraph position="18"> In declarative contexts, this rule works quite well. It corresponds essentially to the focus rule of Sidher (1981). In a question-answering situation it is hardly applicable, since especially in wh-questions subject position and word order, which both play a role, tend to interfere. We therefore tend to not use this rule, but rather to let the system ask back in cases where it would apply. For illustration consider the following examples: (32) Does Spain border Portugal? What is its population? null (33) Is Spain bordered by Portugal? What is its population? (34) Which country borders Portugal? What is its population? (35) Which country does Portugal border? What is its population? P5. Accusative object noun phrases are preferred over other non-subject noun phrases.</Paragraph> <Paragraph position="19"> P6. Noun phrases preceding the pronoun are preferred over noun phrases succeeding the pronoun (or: anaphora is preferred over kataphora).</Paragraph> </Section> <Section position="3" start_page="149" end_page="149" type="sub_section"> <SectionTitle> 3.3 Outline of a pronoun resolution procedure </SectionTitle> <Paragraph position="0"> We now outline a procedure for &quot;resolving&quot; pronouns in the framework of the USL system and DRT.</Paragraph> <Paragraph position="1"> Let M = <U, Con> be the DRS representing the mutual knowledge, in particular the past discourse. Let K(s) be the DRS representing the current sentence s and let p be a pronoun occurring in s for which an appropriate discourse referent has to be found. Let U be the set of discourse referents a(p) accessible to p according to the accessibility relation given in sec. 2.2 Let further c be a function that a;)plies to U a(p) all the morphological, syntactic, and semantic criteria, given above and yields a set Uc(p) as result. Now three cases have to be distinguished: 1. Uc(p) is empty. In this case the use of p was inappropriate.</Paragraph> <Paragraph position="2"> 2. Card(Uc(p)) is 1. In this case a referent for p has been uniquely determined, p is replaced by it in the DRS, and the procedure is finished.</Paragraph> <Paragraph position="3"> 3. Card(Uc(p)) is greater than 1. In this case the preference rules are applied.</Paragraph> <Paragraph position="4"> Let p be a function that applies to Uc(p) if the cardinality of Uc(p). is greater than 1 all the preference rules given above in the order indicated there yielding the result Up. Card(Up) can never be 0, hence two cases are possible, either the cardinality is 1, then a referent has been uniquely determined and the pronoun p can be eliminated in K, or the cardinality is greater than 1, and then the use of p was inappropriate.</Paragraph> <Paragraph position="5"> It can be inferred from the formulation of the pronominalization rules given above, what morphological and syntactic information has to be stored with the discourse referents in the DRSs, and what semantic information has to be accessible from the schema of the database to enable the application of the functions c and p. Hence, we will not spell out these details here.</Paragraph> </Section> </Section> <Section position="4" start_page="149" end_page="150" type="metho"> <SectionTitle> 4 Open questions and conclusions </SectionTitle> <Paragraph position="0"> Many well-known and puzzling cases have not been addressed here, among them plural anaphora, so-called pronouns of laziness, one pronominalization, to name just a few.</Paragraph> <Paragraph position="1"> We have not said anything about phenomena such as discourse topic, focus, or coherence and their influence on anaphora. Their effects are captured in our preference rules to some degree, but no one can precisely say how. Inspire of claims to the contrary, we believe that much work is still required, before these notions can be used effectively in natural language processing.</Paragraph> <Paragraph position="2"> By limiting ourselves to the relatively well-defined communicative situation of database interaction, we have been able to state precisely, what rules are applicable in the fragment of language we are dealing with. We are currently working on the analysis of running texts, but again in a well-delineated domain, and we hope to be able to extend our theory on the basis of the experience gained.</Paragraph> <Paragraph position="3"> We are convinced that serious progress in the understanding of anaphora and of discourse phenomena in general is only possible through a careful control of the environment, and on a solid syntactic and semantic foundation.</Paragraph> </Section> class="xml-element"></Paper>