Berwick Robert C.

Yang Charles D.

English

Yang, Charles D.

49263

Berwick, Robert C.

49264

Waseda University Repository

Language, Information and Computation(PACLIC 11),1996, 363-371Principle-based Parsing for ChineseCharles D. Yang and Robert C. BerwickArtificial Intelligence LaboratoryMassachusetts Institute of Technology545 Technology Square, NE43-769{charles, berwick}@ai.mit.eduAbstractThis paper describes the implementation of Mandarin Chinese in thePappi system, a principle-based multi-lingual parser. We show that sub-stantive linguistic coverage for new and linguistically diverse languagessuch as Chinese can be achieved, conveniently and efficiently, through pa-rameterization and minimal modifications to a core system. In particular,we focus on two problems that have posed hurdles for Chinese linguistictheories. A a novel analysis is proposed for the so-called BA-construction,along with a principled computer implementation. For scoping ambigu-ity, we developed a simple algorithm based on Jim Huang's IsomorphicPrinciple. The implementation can parse fairly sophisticated sentences ina couple of seconds, with minimal addition (less than 100 lines of Prologcode) to the core parser. This study suggests that principle-based pars-ing systems are useful tools for theoretical and computational analysis oflinguistic problems.1 IntroductionNatural languages are complex and their syntactic properties seem to differfrom one another quite dramatically. Traditional parsing technologies utilizelanguage-particular, rule-based formalisms, which usually result in large andinflexible systems (Marcus 1980). For a recent example of the rule-based ap-proach to Chinese parsing, see (Lee et al., 1991).In recent years, computational linguistics has seen the development of thePrinciple-based Parsing (Berwick et al 1991). A principle-based parser transpar-ently reflects the structure of the contemporary linguistic theory, the Principlesand Parameters framework (Chomsky 1981). It is believed that languages areconstrained by a small number of universal principles, with linguistic variationslargely specified by parametric settings.The merit of principle-based parsing is two-fold. As a tool for linguists, itis directly rooted in grammatical theories. Therefore, linguistic problems, par-ticularly those that involve complex interactions among linguistic principles,can be cast in a computational framework and extensively studied by drawingdirectly on an already-substantiated linguistic platform. It is designed fromthe start to accommodate a wide range of languages — not just 'Eurocenteric'363Romance or Germanic languages. Japanese, Korean, Hindi and Bangla haveall been relatively easily modeled in PAPPI (Berwick and Fong 1991, Berwickforthcoming). As a tool for engineering, it inherits the useful design principle ofmodularity among at least some of the principles. Differences among languagesreduce to distinct dictionaries, required in any case, plus parametric variationin the principles.To show how this project may be concretely executed for Chinese, we firstreview the basic phrase structures and parameters for Chinese. Our principlesource is Jim Huang's seminal dissertation (1982). Then we turn to two par-ticular problems that have generated much interest and productive work inthe literature, the BA-construction and the scoping non-ambiguity in Chinese.Both theoretical and computational analyses are presented. The paper con-dudes with some general observations on principle-based parsing, in relationto linguistics and computation.2 Structures and Parameters in Chinese"Chinese exhibits a full range of head-final constructions, but allows only alimited range of head-initial construction" (Huang 1982). Using the X-barschemata for phrase structure, we have:(1) (a) X P -+ Spec(b)	 X Comp, X  nounThe basic X parameters indicate that Chinese has roughly the same word orderas English, except that in the noun phrase case the modifier always precedesthe noun in Chinese. These parameters are specified in a separate file for theparser:%% X-Bar ParametersspecInitial.specFinal	 \+ specInitial.headFinal(n).headFinal(c).headInitial(X)	 headFinal(X).In Chinese, Complex noun phrases consist of a sequence of modifiers (e.g.possessives, adjectives, relative clauses, as in (2.a-c) respectively), followed bya marker de:(2) (a) ta de the (his car)(b) meffi de yanjing (beautiful eyes)(c) ta xihuan de the (the car he likes)364Chinese possessives, such as to in (2.a), are not reflected in surface morpho-logical features, contrary to English (e.g. she her). Therefore, one must becautious because the parser can have no visible information to identify posses.:sives, which then must nevertheless still receive case as in English (sherner). Todeal with this problem, we assume that the morphological marker de assignsgenitive case to the noun or clausal phrase on its left, to prevent a case filterviolation.lex (de ,mrkr , [left (np, case (gen) , [] ) ] ) .lex (de,mrkr, [left (c2 , case (gen) , [ ] ) ] ) .In Chinese, adverbial adjunctions take particular orders (unlike English,which is rather free): time precedes location, which in turn precedes manner:(3) John zuotian zai xuexiao kanjian-le Mary.John yesterday at school saw Mary.We specify adverbial properties with a predicate feature in the lexicons, forexample:lex (zai, p, [grid ( [] , [location] ) ,predicate (location) ] ) .lex (chang, adv, [adjoin (left) , predicate (manner) ] ) .lex (zuotian, adv, [adjoin (left) , predicate (time) ] ) .A simple procedure is written to constrain adjunction orderings.%% Check VP adjunct order: TIME > LOCATION > MANNERrhs [pp (P) ,vp (X) ] add goals [checkVPadj (P, X) ] .rhs [adv (A) , vp (X) ] add goals [checkVPadj (A, X) ] .checkVPadj (Adj 1, VP) : -\+ adjoined (VP) .checkVPadj (Adj 1, VP) : -adjoined (VP, Adj 2 ,VP1) ,precedenceInOrder (Adj 1, Adj 2) ,checkVPadj (Adj 2 , VP1) .precedenceinOrder(Adj1,Adj2) :-Adjl has_feature predicate(time),Adj2 has_feature predicate(location).precedenceinOrder(Adj1,Adj2) :-Adjl has_feature predicate(time),Adj2 has_feature predicate(manner).precedenceInOrder(Adj1,Adj2) :-Adjl has_feature predicate(location),Adj2 has_feature predicate(manner).Like Japanese but unlike English, Wh-movement does not occur overtly inChinese:365(4) (a) Ni da-le shui? (You beat who?)(b) Who did you beat t?This parametric distinction constitutes an important module in the principle-based theory. It has been directly implemented in Pappi. We simply set theparameter to:%% Wh In Syntax Parameterno whInSyntax.Conventionally, Bounding Nodes represent a constraint on how far elementscan be displaced from their canonical argument positions, like who in Who didyou see? Following standard linguistic analyses, in Chinese the bounding nodesare the inflection phrase (II') and NP, similar to Dutch and Italian. Again, thisis straightforwardly implemented in the current system; we simply set thebounding node parameters for Chinese:%% Subjacency Bounding NodesboundingNode(i2).boundingNode(np).These central aspects of Chinese phrase structure are hence readily handledby parametric settings and simple goal-adding mechanisms. We next turn tospecific case studies — beginning with the BA-construction.3 The BA-construction: Theory and ComputationThe BA-construction in (5) has been a perennial problem for Chinese linguists.(5) Wo ba John da-le. (I had John beat)It is perhaps impossible to give a purely syntactic analysis to account for all therich semantic and pragmatic factors (Ding 1991) in BA-constructions. Huang'sanalysis (1982) relies on phrase structure constituency. Li (1990) suggests thatBA-constructions as base-generated. We propose a different approach. We tryto derive BA-construction from syntactic theories on the basis of some semanticconsiderations. The aim is to show that a complex type of construction canbe derived from syntactic principles, unless theoretically proven otherwise.Stipulations such as base-generation rules are taken as a "last-resort", whichinvolves language-particular peripheral mechanisms, an effort we try to avoidor postpone in principle-based syntactic analysis.The first step is to determine the categorical nature of ba. There are twoobvious possibilities: ba as a preposition or as a verb. It is not difficult toeliminate the former, on the basis of the so-called Theta Criterion (Chomsky1981), that every thematic role like Agent, Patient, etc. must be uniquelyassigned and every argument must be receive one and only one theta role (a366standard assumption also used many current theories, such as LFG, HPSG,and the like). If ba were a preposition, its thematic role (oblique) must bedischarged. The only possible recipient of its thematic role is John, which hasalready received the patient role from da - a contradiction. Thus ba must be averb.The second step draws motivations from semantic considerations. We notethat in BA-constructions, there is an observable semantic predicate shift of main(sentential) action emphasis from the transitive verb phrase in (6a) to the verbalphrased headed by ba (dubbed BaP henceafter) in (6b)(6) (a) Wo [yp da-le John].(b) Wo [Bap ba John da-le].On surface, John superficially looks like the direct object of ba. However, al-though it is reasonable to assume BaP becomes the main action predicate ofthe sentence (as the result of semantic predicate shift), John still receives its the-matic role from da (beat) in semantic interpretation, contrary to the superficialintuition. Therefore, we conclude that John must have moved from its originalthematic position in (5).The third step answers the following question: If John is displaced in (5),what triggers this movement from its original thematic position? This disloca-tion cannot be driven to place John in a thematic-role receiving position, sinceJohn is understood as the recipient of the patient-role from da Therefore, theonly syntactic parsing option we are left with for must be case-related.The question then becomes, Why cannot John receive case from its thematicrole assigner, da? This leads to the fourth and last step in our analysis. We pro-pose that in the BA-construction, the original action verb (e.g. da in (5)) loses itscase-assigning ability, much like BEI passivized verbs or passive verbs in En-glish. We draw this conclusion from the well-known BA and BEI constructionparallelism, as follows.As usually manifested in routine Chinese grammar exercises, there existsa one-to-one mapping between BA and BEI constructions. That is, any BAconstruction has a BEI counterpart - passivization in Chinese, and vice versa:(7) (a) Wo BA John da-le. (I beat John.)(b) John BEI wo da-le. (John was beaten by me.)Given this parallel contrast, we suppose that the BA-construction is in factanalogous to the BEI-construction, i.e. passivization. As quite standardlyassumed, passivized verbs lose their case-marking ability; thus, the verb in theBA-construction loses its case-marking ability as well.Therefore, a clear analysis is in sight. In BA constructions, the action verb (dain (5)) loses case-assigning ability as in passivization; its direct object is forcedto move to the object position of BA to receive case. BA, on the other hand, is alight verb that has no thematic role to assign, but is able to Exceptionally CaseMark (ECM) into a small clause, i.e. the action verbal phrase:367(8)II 	BaPba	 VPJohni VPV tidaHaving worked out a plausible theory, implementation becomes straight-forward. We take the following steps:(9) (a) Mark the lexical features of ba with the properties:• take a verb phrase small dause• have 'exceptional' case marking ability• blocks the verb's case-marking ability(b) Allows overt NP (the object) to adjoin VP, creating the subject posi-tion for the small dause to facilitate ECM to take place.4 Scoping UnambiguityThe well-known quantifier scoping ambiguities in English do not exist in theirChinese counterparts:(10) (a) Every man loves a woman.i. For every man x, there exists one woman y such that x loves y.ii. For every man x, there exists a woman y, such that x loves y.(b) Meige nanren dou xihuan yige nuren."Everyman likes one woman."A valuable analysis is suggested by Aoun and Li (1992). They assume thatthe subject is generated within the verbal projection (VP), and that in English,the subject raises the Specifier position (Le., the traditional 'subject' position;'specifier' is the familiar X-bar terminology for the same) of the inflection phrase(P) but not in Chinese,because Chinese has no subject-verb agreement and thusis "inflectionally impoverished". This (parametric) optionality allows multiplelanding sites in English, but not in Chinese, for Quantifier Raising (May 1985)that occurs at LF - thus, ambiguity in English and non-ambiguity in Chinese(see (Aoun and Li 1992) for details).368This analysis, although reasonable and principled, is fairly complex andrequires a few more crucial syntactic principles that have yet been implementedin PAPPI. Instead, in order to maintain system integrity and computationalefficiency, we develop a practical solution that attributes the scoping contrastto Huang's Isomorphic Principle (1982):(11) The Isomorphic PrincipleIf a quantifier phrase QP A c-commands QP B at phrase structure (S-structure), then it does so at logical form (LF) as well.Crucially, we view the Isomorphic Principle as a parametric variation betweenChinese and English. In particular, we assume that(12) (a) The Isomorphic Principle is applicable to QR in Chinese.(b) The Isomorphic Principle is not applicable to QR in English.We introduce a language parameter, isomorphicPrinciple and set itTRUE for Chinese and FALSE for English, in their parameter files, respectively.This parameter is then called upon as a LF condition on QR.1fMovement(SS,LF) :-qr(SS,SS1),checkIsomorphic(SS1) if isomorphicPrinciple,moveWh(SS1,LF).checkIsomorphic(SS1) :-qrT(SS1,TIs),qrQ(SS1,QIs),TIs == QIs.qrT collect I in_All_configurations CF where CF has_feature ec(qr),CF has_feature index(I).qrQ collect I in_all_configurations CF where CF has_feature moved(qr),CF has_feature index(I).In Chinese, we observe that QP a c-commands )3 if and only if a precedes )3at LF and S-Structure. In the implementation above, we collect two lists ofitem: one with QPs after QR (precedence at LF), the other with QPs at basepositions (precedence at S-Structure). If the Isomorphic Principle holds, the twolists must have identical orderings. In other words, we reconstruct S-Structureinformation from LF representations. The computational effort is minimal.5 Results and conclusionsOverall, the implementation is quite simple, summarized as follows:1. A dictionary is constructed, which contains lexical entries for words usedin the implementation.3692. Chinese-particular parametric values are determined through linguisticliterature, for the X-bar theory, the Bounding theory, the movement theory,etc.3. Some Chinese-particular, linguistically interesting problems are consid-ered, e.g. the BA-construction and scoping unambiguity. Theoreticalsolutions are proposed and implemented as language peripheral compo-nent of the parsing systemWe are able to parse sentences with the range of structures including Whmovement, the Binding Theory, Quantifier Scoping, the BA-construction tocomplex NP (clausal, possessive, and numeral/ dassifier). All testing sentencesare correctly analyzed: LF logical form representations are computed for thegrammatical sentences and the ungrammatical ones are ruled out ones withlinguistic principle violation(s) shown. Each parse takes no more than 2 secondson a Sparc 10 workstation. Overall, excluding a hand-wired dictionary, less than100 additional lines of Prolog are required.Because the Pappi system implements its model linguistic theory faithfully,adapting new languages is expected to be quite minimal, as our implementationshows. Additionally, it provides a platform on which linguists can experimenttheoretical proposals extensively and also cross-linguistically, without havingto know much about the internal design of the parser. Furthermore, principle-based systems output very rich and accurate structural descriptions, includinglogical form representations, that assist in more engineering-oriented NLP tasksthat go beyond parsing (Lin 1995).6 References1. Aoun, Joseph and Audrey Li. (1992). The Syntax of Scope. MIT Press,Cambridge, MA.2. Berwick, Robert C., editor. (forthcoming). Principle-Based Parsing: FromTheory to Practice. Kluwer Academic Publishers, Norwell, MA.3. Berwick, Robert C., Abney, Steven, and Carol Tenny., editors (1991).Principle-Based Parsing: Computation and Psycholinguistics. Kluwer Aca-demic Publishers, Norwell, MA.4. Berwick, Robert C., and Sandiway Fong. (1993). Madama ButterflyRedux: parsing English and Japanese with a principles and parametersapproach. In R. Mazuka and N. Nagai (eds). Japanese Sentence Processing.Hillsdale, NJ: Erlbaum. 177-208.5. Chomsky, Noam. (1981). Lectures on Government and Binding. Foris,Dordrecht, Holland.3706. Ding, Shizhi. (1991). Ba-constructions typology in mandarin Chinese:A government-binding approach. Master's thesis, University of BritishColumbia.7. Fong, Sandiway. (1991). Computational Properties of Principle-Based Gram-.matical Theories. PhD thesis, MIT, Cambridge, MA.8. Huang, James. (1982). Logical Relations in Chinese and the Theory of Gram-mar. PhD thesis, MIT, Cambridge, MA.9. Lee, L. S., Chien, L. F., Lin, L. J., Huang, J., and Chen, K. J. (1991). Anefficient natural language processing system specially designed for theChinese language. Computational Linguistics, 17(4).10. Li, Audrey. (1990). Order and constituency in Mandarin Chinese. KluwerAcademic Publishers, Norwell, MA.11. Lin, Dekang. (1995). Talk given at the ARPA Message UnderstandingConference (MUC).12. Marcus, Mitch. (1980). A Theory of Syntactic Recognition for Natural Lan-guage. MIT Press, Cambridge, MA.13. May, Robert. (1985). Logical Form. MIT Press, Cambridge, MA.

Principle-based Parsing for Chinese

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Principle-based Parsing for Chinese

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