Chan Y.W.

Ho H.C.

Lai B.Y.

Lun S.C.

T\u27sou B.K.

English

DSpace at Waseda University

Using Syntactic Markers and Semantic FrameKnowledge Representation inAutomated Chinese Text AbstractionH. C. Ho, B. K. T'sou, Y. W. Chan, B. Y. Lai k S. C. LunCity Polytechnic of Hong KongAbstractAutomated Chinese Full-text Abstraction System (ACFAS) 1 is a majorcomputational linguistics research project at the City Polytechnic of HongKong. It aims to automatically produce abstracts from Chinese newspapereditorials in Hong Kong. The abundant use of overt syntactic markers typicalin argumentative texts has been capitalized as cues to establish the textualstructure of the input. On the basis of analyses of a corpus of editorials, theadequacy of this use of syntactic markers is investigated, and issues related tohow they can be used in the construction of a semantic frame knowledgerepresentation are studied.1. IntroductionThe paraphrase and condensation of written information (text abstraction) is a common andunique human faculty. Scientific research in this area provides important clues to thehuman cognition process and has direct relevance to both disciplines of linguistics andcomputer science.Automated text abstraction, based on machine understanding of the input text, relies onseveral central capabilities : grammatical knowledge for analyzing the input text and forproducing well-connected and natural prose in the output abstract; knowledge of thedomain of discourse for a proper interpretation of the semantic and pragmatic aspects of theinput text; logical inference ability for ensuring consistency and coherence. AutomatedChinese Full-text Abstraction System (ACFAS) is an attempt at producing abstracts directlyfrom input texts. The scope of the project is predetermined by two parameters : (1) theoriginal text, in the form of Chinese newspaper editorials and commentaries, will bemanually pre-edited (minimally, to remove non-standard language usage) before beingsubmitted to the system as input; and (2) the domain of discourse is defined to be the safety1 Supported by Grant No.904067 from the Research Grants Council of the University and PolytechnicGrants Committee of Hong Kong.122of the nuclear power plant at Daya Bay. The conception of ACFAS and the direction of itsinvestigative efforts are motivated by, and based on, experience gained from earlier work incomputer-assisted text abstraction [6].The focus of the current research effort in ACFAS is on issues related to the process ofknowledge abstraction, as conducted by humans and by machines, and to the explorationof optimal knowledge structures to support natural language understanding in a restricteddomain. This paper first discusses the role of syntactic markers in the presentation ofargumentation commonly encountered in newspaper editorials and commentaries. Aknowledge representation scheme designed to capture the essence of the argumentativediscourse, as indicated by these syntactic markers, is then proposed. This is followed byan example to illustrate the ideas presented, and a conclusion which highlights thesignificance of the proposal and areas of future work.2. Using syntactic markers in text analysisIn argumentative discourse, the chains of reasoning are commonly and explicitly indicatedby syntactic markers that express the rhetorical relationship amongst the constituentpropositions. Previous work on rhetorical structures for argumentative Chinese text [3] hasidentified two types of rhetorical relationships :(i) Subordination relationshipThis is an asymmetric (PIANZHENG Oil) relationship involving a minimum of twopropositions, the first of which is a precedent and the second a derivative.The function ofeach of these propositions can be clearly identified by clause-initial or post-topic syntacticmarkers. These markers are typically conjunctions, adverbs, modal verbs and the twopropositions are often linked by syntactic markers, manifested as paired discontinuousconstituents. The subordination relationship may be sub-categorized as follows:(a) sufficiency (e. g. apa..gt "if .. then")(b) necessity and sufficiency (e.g.	"only .. if')(c) causality (e.g. Ina _Ma "because .. therefore")(d) deduction (e.g. KM ..griff "since .. then")(e) adversativity (e.g. gem. .gjg "although .. but")(f) concession (e.g. U11.. PA "even if .. still")(ii) Coordination relationshipThis is a symmetric (LIANHE efe) relationship involving a minimum of twopropositions, which are parallel and bear no precedent/derivative relationship to each other.The ordering of the two propositions is not significant in terms of argumentative structurebut may signify emphasis or other rhetorical needs. The syntactic markers are againusually paired discontinuous constituents. This type of symmetric relationship may beclassified into three sub-categories:(a) conjunction (e.g. tit. .3Z "both .. and")123(b) disjunction (e.g. ag gm "or .. or")(c) progression (e.g. TN. .ffifi "not only .. but also")The syntactic markers can be used in combination to provide a very powerful way ofarticulating logical argument in Chinese discourse. As such, they provide important cues intext analysis and understanding. A tabulation of the more commonly used syntacticmarkers for each rhetorical relation is given in the Appendix.To construct abstracts of editorials (which are inherently argumentation-based), afundamental requirement is the ability to extract the flow of argumentation. The frequencyof occurrence of rhetorical syntactic markers can be a good measure of the argumentativecontent of an editorial. The research reported here is based on, among other sources, acorpus of 16 newspaper editorials. An analysis of this corpus has indicated that thesesyntactic markers are used fairly frequently. Of the 961 sentences in the corpus, syntacticmarkers appear in 342 -- about 36%. This is certainly a very high figure, given that, asexpected, editorials normally devote substantial efforts to present plain facts, figures andexamples to support the intended arguments. It is noteworthy that in this genre of writing,the average word length is 2.5 characters and the average sentence length is 38.5 charactersor 23.3 words. This points to an overabundance of complex sentences.Some syntactic markers are used very heavily. For the sample corpus, the followingmarkers appear more than ten times. Some as many as 80 times."but""because""therefore""although .. but""plus""but"'even .. if'While it is recognized that not all arguments in editorials are explicitly indicated, it can beseen that syntactic markers provide effective cues for tracing the major flow ofargumentation.In actual running texts, the syntactic markers with paired discontinuous constituents maynot be both realized in the surface form. Depending on the context, one or even both maynot appear. Moreover, the ordering of the subordinate constituents might enjoy somedegree of freedom because of a number of factors, such as individual style, Europeanizedsyntax, and the effect of suspense etc.1243. Knowledge representation for abstractsInference trees have been proposed for the structuring of argumentative discourse [3], andthe use of syntactic markers to guide the conceptual construction of inference trees has alsobeen studied [7]. In this section, we propose a representation scheme that acts as anintermediary between the output from the syntactic parser and the target inference trees.This divide-and-conquer approach permits a separation of focus : first on the processing ofsurface-level rhetorical relationships, and then on the transformation of these rhetoricalrelationships into deeper-structure inference trees.The intermediate representation scheme is based on frames. A frame representation isselected because of its expressive power and the scope it offers for exploiting the use ofinheritance. Since a unit of argumentative discourse is composed of syntactic markers thatimpose rhetorical relationships upon constituent propositions (statements), there are twocorresponding types of frames : rhetorical frames and statement frames.3.1 Rhetorical framesRhetorical frames are used for representing the rhetorical relationships discussed in thepreceding section. Thus there are two types of frames : Subordination frames andCoordination frames. The organization of the frames is first described, followed by anillustrative example.3.1.1 Subordination frameA Subordination frame captures the rhetorical relationship between a set of propositions(the precedent) and the corresponding conclusions (derivative). It has 3 slots :(a) Rhetorical relationship categoryIndicating one of :sufficiencynecessity and sufficiencycausalitydeductionadversativityconcession(b) Precedent linkA reference to :either another Subordination frameor	 a Coordination frame(c) Derivative linkA reference to :either a Subordination frameor	 a Coordination frame1253.1.2 Coordination frameA Coordination frame is used for conjoining parallel propositions. There are 3 slots :(a) Rhetorical relationship categoryIndicating one of :conjunctiondisjunctionprogressionnull (to signify end of Coordination chain)(b) Anchor linkA reference to :either a Subordination frameor	 a Statement frame (discussed in Section 3.2)(c) Next linkA reference to :either another Coordination frameor	 null313 An exampleFor the following sentence:INAA,	 PfiAC."Because A, meanwhile B, therefore C."where A, B, and C are simple statements (discussed in section 3.2), the rhetorical framestructure consists of one Subordination frame and three Coordination frames:Subordination frame :Rhetorical relationship category : causalityPrecedent link	: Coordination frame (1)Derivative link	: Coordination frame (3)Coordination frame (1) :Rhetorical relationship category : conjunctionAnchor link	 : Statement frame (1){ representingproposition A }Next link	: Coordination frame (2)126Coordination frame (2) •Rhetorical relationship category : nullAnchor link	 : Statement frame (2){ representingproposition B }Next link	 : nullCoordination frame (3) :Rhetorical relationship category : nullAnchor link	 : Statement frame (3)representingproposition C }Next link	 : null3.2 Statement framesA statement frame is the internal representation of a basic building block of anargumentative discourse unit. In the present context, a basic building block is a piece oftext that does not contain syntactic markers (call this a simple statement). Statement framesare thus used for storing the domain-specific knowledge corresponding to the contents ofthe corresponding text.The design and construction of large knowledge bases for natural language understandinghave been widely studied [1,2,4]. It is outside the scope of our present endeavor toembark on a task of comparable scale. For our investigative study, we propose a frame-based hierarchy, with ideas drawn from the work of S. H. Teng [5].For discussion purposes, we present two example types of frames, namely :(1) ActionAn event involving an active agent, such asA manages B.The "manage" frame instance has slots :agent : Apatient : B127(2) StateA description of a situation, such asX is trustworthy.The "trustworthy" frame instance has slot :patient : XThe integration of these statement frames with rhetorical frames for representing anargumentative sentence is illustrated through an example in the next section.4. An exampleThe following sentence is used to illustrate the overall frame representation scheme :tittitAt01.111141M114), tisa,	 leARSIN"Since Hong Kongers have confidence in foreign experts, then, if they are in charge ofthe management of Daya Bay Nuclear Power Plant, Hong Kongers will believe thatchances of nuclear accidents will be decreased to the minimum."There are two rhetorical relations :(1) deduction gm Ase "since .. then"(2) sufficiency pog..itt "if .. then"The simple statements are(1)isAciflin*vaz "Hong Kongers have confidence in forerign experts"(2) Fiilitiammta "they are in charge of the management of Daya Bay NuclearPower Plant"(3) itAttittlifatal,PMIttgla "Hong Kongers will believe thatchances of nuclear accidents will be decreased to the minimumThe frame structure consists of 5 rhetorical frames (2 Subordination frames, 3Coordination frames) and 4 Statement frames. It should be noted here that the derivation ofthe frame representation scheme is based on the assumption that adequate semanticprocessing of the simple statements has been performed at an earlier stage, to achieve, forinstance, anaphora resolution and suitable mapping of propositions onto , predefinedstatement frames.Subordination frame (1) :Rhetorical relationship category	 : deductionPrecedent link	: Coordination frame (1)Derivative link	 : Subordination frame (2)128Subordination frame (2) :Rhetorical relationship categoryPrecedent linkDerivative linkCoordination frame (1) :Rhetorical relationship categoryAnchor linkNext linkCoordination frame (2) :Rhetorical relationship categoryAnchor linkNext linkCoordination frame (3) :Rhetorical relationship categoryAnchor linkNext link: sufficiency: Coordination frame (2): Coordination frame (3): null: Statement frame (1)• null• null: Statement frame (2): null• null: Statement frame (3)• nullStatement frame (1) :frame type	 :	 "have confidence"subclass of	 : statepatient	 : itA "Hong Konger"goal	 : BFI* "foreign expert"Statement frame (2)frame type	 : 'VI "manage"subclass of	 : actionagent	 : Min* "foreign expert"patient	 : i "Daya Bay Nuclear Power Plant"Statement frame (3)frame type	: MI "believe"subclass of	 : statepatient	 : taA "Hong Konger"goal	 : statement frame (4)129Statement frame (4)frame type	 : Vt "safe"subclass of	 : statepatient	 :	 "Daya Bay Nuclear Power Plant"goal	 : null5. ConclusionFrom an analysis of a sample corpus of Chinese newspaper editorials and commentaries, ithas been demonstrated that syntactic markers have a significant role to play in the analysisof argumentative discourse. These markers provide useful guidance for isolating individualpropositions, as well as identifying the rhetorical relationships among the propositions.Based on these findings, a knowledge representation scheme for capturing the rhetoricalstructures has been proposed. The scheme, which uses frames, is conceptually simple, yetpowerful and flexible enough to accommodate future extensions. Further work in theACFAS project will address issues concerning the transformation from parser output to theframe representation, and thence to inference trees for subsequent text generation.References[1] Barnett, J., Knight, K., Mani, I. and Rich, E. "Knowledge and Natural LanguageProcessing." Communications of the ACM, Vol. 33, No. 8 (August 1990), pp. 50-71.[2] Lenat, D.B., Guha, R.V., Pittman, K., Pratt, D. and Shepherd, M. "Cyc : TowardPrograms with Common Sense." Communications of the ACM, Vol. 33, No. 8 (August1990), pp. 30-49.[3] Lin, H.L., T'sou, B.K., Ho, H.C., Lai, B.Y.T., Lun, S.C., Choi, C.Y. and Kit,C.Y. "Automatic Chinese Text Generation Based on Inference Trees." In Proceedings ofthe ROCLING 1991 Computational Linguistics Conference IV (Taiwan, 1991), pp. 215-236.[4] Nirenburg, S., Monarch, I. and Kaufmann, T. "World Knowledge and TextMeaning." In The KBMT Project: a case study in knowledge- based machine translation,K. Goodman, S. Nirenberg (Eds.). Morgan Kaufmann Publishers (1991), pp. 17-48.[5] Teng, S.H. A Semantic study of transitivity Relations in Chinese. Student Book Co.Taipei (1976).[6] T'sou, K.B., Ho, H.C., Lai, B.Y.T., Lun, S.C. and Lin, H.L. "A Knowledge-basedMachine-aided System for Chinese Text Abstraction." In Proceedings of the 14thInternational Conference on Computational Linguistics (Nantes, 1992), Vol. 3, pp. 1039-1042.[7] T'sou, K.B., Ho, H.C., Lai, B.Y.T., Lun, S.C. and Lin, H.L. "FromArgumentative Discourse to Inference Trees : Using Syntactic Markers as Cues in ChineseText Abstraction." In Proceedings of the 3rd International Conference on ChineseInformation Processing (Beijing, 1992), pp. 76-93.130AppendixRhetoricalRelationConj.-pair1 2SUFFICIENCYMOWPIA ' W13*gi WI- rEi ( WI )IRtt WIau (a)M itRNA -t/4NM 41i3*WA it( * ) E/17:'NECESSITY R- 4-ANDRw aSUFFICIENCY1$41311* ffMda)sl, ,,,CAUSAL! TY u ( A ) Pfrf Au MOW EtiY§ ElkEM (NT)- - - - u it____ tat---- WffDEDUCTION KA (,.L	 )fft : ii Mt% - - - - EtitEffn- - - TIN,- - - - giADVERSAT I V I TY ifit fiAOffillig Olt MR- )- - - - TA- - - - AltRhetoricalRelationConj.-pair1 2CONCESS I ON RNA ITYt31-Stritg ite, -tAtfZit. „ ('TA )CONJUNCT I ON - - - - • To-AIMP* 1*--T *Z.- -.ffl ---.ffl-* :=3KRt R/t,R R......... Roe- - - - IJii_h( W) E.- - - - "ARDISJUNCTION VA- A-1311i*Nlif* - - - - A ( 4 )Wif 5PROGRESSION T ti,Li 'Mg_'MK TR *Y- - - - AW- - - - X131

Using Syntactic Markers and Semantic Frame Knowledge Representation in Automated Chinese Text Abstraction

Ho, H.C.

48980

T'sou, B.K.

48981

Chan, Y.W.

48982

Lai, B.Y.

48983

Lun, S.C.

48984

Waseda University Repository

https://waseda.repo.nii.ac.jp/?action=repository_action_common_download&item_id=28410&item_no=1&attribute_id=101&file_no=1

Using Syntactic Markers and Semantic Frame Knowledge Representation in Automated Chinese Text Abstraction

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