A LINK GRAMMAR FOR TURKISH A THESIS SUBMITTED TO THE DEPARTMENT OF COMPUTER ENGINEERING AND THE INSTITUTE OF ENGINEERING AND SCIENCES OF BILKENT UNIVERSITY IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE By Özlem İstek August, 2006 I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a thesis for the degree of Master of Science. Asst. Prof. Dr. İlyas Çiçekli (Supervisor) I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a thesis for the degree of Master of Science. Prof. Dr. H. Altay Güvenir I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a thesis for the degree of Master of Science. Assoc. Prof. Ferda Nur Alpaslan Approved for the Institute of Engineering and Sciences: Prof. Dr. Mehmet Baray Director of Institute of Engineering and Sciences ii ABSTRACT A LINK GRAMMAR FOR TURKISH Özlem İstek M.S. in Computer Engineering Supervisor: Asst. Prof. Dr. İlyas Çiçekli August, 2006 Syntactic parsing, or syntactic analysis, is the process of analyzing an input sequence in order to determine its grammatical structure, i.e. the formal relationships between the words of a sentence, with respect to a given grammar. In this thesis, we developed the grammar of Turkish language in the link grammar formalism. In the grammar, we used the output of a fully described morphological analyzer, which is very important for agglutinative languages like Turkish. The grammar that we developed is lexical such that we used the lexemes of only some function words and for the rest of the word classes we used the morphological feature structures. In addition, we preserved the some of the syntactic roles of the intermediate derived forms of words in our system. Keywords: Natural Language Processing, Turkish grammar, Turkish syntax, Parsing, Link Grammar. iii ÖZET TÜRKÇE İÇİN B İR BA Ğ GRAMER İ Özlem İstek Bilgisayar Mühendisli ği Bölümü, Yüksek Lisans Tez Yöneticisi: Yar. Doç. Prof. Dr. İlyas Çiçekli Ağustos, 2006 Sözdizimsel çözümleme veya ayrı ştırma, bir tümcenin dilbilgisel yapısını yani kelimeleri arasındaki ili şkiyi ortaya çıkarmak amacıyla verilen bir gramere göre inceleme i şlemidir. Bu çalı şmada, Türkçe için bir ba ğ grameri geli ştirilmi ştir. Sistemimizde Türkçe gibi çekimli ve biti şken biçimbirimlere sahip diller için çok önemli olan, tam kapsamlı, iki a şamalı bir biçimbirimsel tanımlayıcının sonuçları kullanılmı ştır. Geli ştirdi ğimiz gramer sözcükseldir ancak, bazı i şlevsel kelimeler oldukları gibi kullanılırken, di ğer kelime türleri için kelimelerin kendilerinin yerine biçimbirimsel özellikleri kullanılmı ştır. Ayrıca sistemimizde kelimelerin ara türeme formlarının sözdizimsel rollerinin bazıları muhafaza edilmi ştir. Anahtar Kelimeler: Do ğal Dil İş leme, Türkçe Dilbilgisi, Türkçe sözdizimi, Sözdizimsel Çözümleme, Ba ğ Grameri. iv Acknowledgement I would like to express my deep gratitude to my supervisor Asst. Prof. Dr. İlyas Çiçekli for his invaluable guidance, encouragement, and suggestions throughout the development of this thesis. I would also like to thank Prof. Dr. H. Altay Güvenir and Assoc. Prof. Ferda Nur Alpaslan for reading and commenting on this thesis. I would like to thank my friends Abdullah Fi şne and Serdar Severcan for their help. I am also grateful to my friend Arif Yılmaz for his invaluable help, moral support, encouragement and suggestions. I am grateful to my family for their infinite moral support and help throughout my life. v To my mother, Fatma İSTEK vi Contents 1 Introduction..................................................................................................1 1.1 Linguistic Background.............................................................................3 1.2 Thesis Outline..........................................................................................7 2 Link Grammar .............................................................................................8 2.1 Introduction.............................................................................................8 2.2 Main Rules of the Grammar.....................................................................9 2.3 Language and Notion of Link Grammars ............................................... 10 2.3.1 Rules for Writing Connector Blocks or Linking Requirements........ 10 2.3.2 The Concept of Disjuncts................................................................12 2.4 General Features of the Link Parser .......................................................13 2.5 Special Features of the Dictionary..........................................................14 2.6 Coordinating Conjunctions ....................................................................17 2.6.1 Handling Conjunctions ...................................................................18 2.6.2 Some Problematic Conjunctional Structures.................................... 20 2.7 Post-Processing .....................................................................................21 2.7.1 Introduction ....................................................................................21 2.7.2 Structures of Domains.....................................................................21 2.7.3 Rules in Post Processing .................................................................22 3 Turkish Morphology and Syntax............................................................... 24 3.1 Distinctive Features of Turkish ..............................................................24 3.2 Turkish Morphotactics...........................................................................28 3.2.1 Inflectional Morphotactics ..............................................................29 3.2.2 Derivational Morphotactics.............................................................33 3.2.3 Question Morpheme........................................................................37 3.3 Constituent Order in Turkish..................................................................38 vii 3.4 Classification of Turkish Sentences .......................................................40 3.4.1 Classification by Structure ..............................................................41 3.4.2 Classification by Predicate Type .....................................................42 3.4.3 Classification by Predicate Place.....................................................44 3.4.4 Classification by Meaning...............................................................44 3.5 Substantival Sentences...........................................................................45 4 Design.......................................................................................................... 47 4.1 Morphological Analyzer ........................................................................47 4.1.1 Turkish Morphological Analyzer ....................................................47 4.1.2 Improvements and Modifications to Turkish Morphological Analyzer ................................................................................................................ 49 4.2 System Architecture...............................................................................52 5 Turkish Link Grammar............................................................................. 61 5.1 Scope of Turkish Link Grammar............................................................63 5.2 Linking Requirements Related to All Words.......................................... 63 5.3 Compound Sentences, Nominal Sentences, and the Wall ....................... 67 5.4 Linking Requirements of Word Classes .................................................74 5.4.1 Adverbs ..........................................................................................74 5.4.2 Postpositions...................................................................................76 5.4.3 Adjectives and Numbers .................................................................78 5.4.4 Pronouns.........................................................................................81 5.4.5 Nouns .............................................................................................85 5.4.6 Verbs.............................................................................................. 90 5.4.7 Conjunctions...................................................................................93 6 Performance Evaluation ............................................................................ 95 7 Conclusion ................................................................................................ 101 BIBLIOGRAPHY ....................................................................................... 103 A Turkish Morphological Features ............................................................ 106 viii B Summary of Link Types.......................................................................... 108 C Input Document and Statistical Results.................................................. 112 D Example Output from Our Test Run...................................................... 113 ix List of Figures Figure 1 METU-Sabancı Turkish Treebank.......................................................3 Figure 2 Typical Order of Constituents in Turkish...........................................39 Figure 3 Architecture of a Two Level Morphological Analyzer ....................... 48 Figure 4 System Architecture