Introduction Dependency Grammar Introduction to Dependency Grammar ◮ Not a coherent grammatical framework: wide range of different kinds of DG ◮ just as there are wide ranges of ” generative syntax” ◮ Different core ideas than phrase structure grammar HS Current Approaches to Dependency Parsing ◮ We will base a lot of our discussion on Mel’ˇ SS 2010 cuk (1988) Dependency grammar is important for those interested in CL: ◮ Increasing interest in dependency-based approaches to Thanks to Markus Dickinson, Joakim Nivre and Sandra K¨ ubler. syntactic parsing in recent years (e.g., CoNLL-X shared task, 2006) Introduction to Dependency Grammar 1(29) Introduction to Dependency Grammar 2(29) Introduction Introduction Overview: constituency Overview: dependency Syntactic structure consists of lexical items, linked by binary asymmetric relations called dependencies. (1) Small birds sing loud songs obj sbj What you might be more used to seeing: nmod nmod S Small birds sing loud songs NP VP sing NP sbj obj Small birds sing birds songs loud songs nmod nmod small loud Introduction to Dependency Grammar 3(29) Introduction to Dependency Grammar 4(29)
Introduction Introduction Constituency vs. Relations Simple relation example ◮ DG is based on relationships between words, i.e., dependency relations For the sentence John loves Mary , we have the relations: ◮ A → B means A governs B or B depends on A ... ◮ Dependency relations can refer to syntactic properties, ◮ loves → subj John semantic properties, or a combination of the two ◮ loves → obj Mary → Some variants of DG separate syntactic and semantic relations by representing different layers of dependencies Both John and Mary depend on loves , which makes loves the head, ◮ These relations are generally things like subject, or root , of the sentence (i.e., there is no word that governs loves ) object/complement, (pre-/post-)adjunct, etc. ◮ The structure of a sentence, then, consists of the set of ◮ Subject/Agent: John fished. pairwise relations among words. ◮ Object/Patient: Mary hit John . ◮ PSG is based on groupings (called phrases or constituents ) ◮ Grammatical relations are not usually seen as primitives, but as being derived from structure Introduction to Dependency Grammar 5(29) Introduction to Dependency Grammar 6(29) Introduction Introduction Dependency Structure Terminology p Superior Inferior Head Dependent obj pc Governor Modifier sbj nmod nmod nmod nmod Regent Subordinate . . . . . . Economic news had little effect on financial markets . Introduction to Dependency Grammar 7(29) Introduction to Dependency Grammar 8(29)
Introduction Introduction Notational Variants Notational Variants had p sbj VBD obj p sbj news effect . obj nmod nmod nmod NN NN PU nmod nmod nmod Economic little on pc pc JJ JJ IN NNS markets nmod nmod JJ financial Economic news had little effect on financial markets . Introduction to Dependency Grammar 9(29) Introduction to Dependency Grammar 9(29) Introduction Introduction Notational Variants Notational Variants p p obj pc obj pc sbj sbj nmod nmod nmod nmod nmod nmod nmod nmod Economic news had little effect on financial markets . Economic news had little effect on financial markets . Introduction to Dependency Grammar 9(29) Introduction to Dependency Grammar 9(29)
Introduction Introduction Phrase Structure Comparison S ◮ Dependency structures explicitly represent ◮ head-dependent relations (directed arcs), VP ◮ functional categories (arc labels), NP ◮ possibly some structural categories (parts-of-speech). ◮ Phrase structures explicitly represent PP ◮ phrases (nonterminal nodes), NP NP NP PU ◮ structural categories (nonterminal labels), ◮ possibly some functional categories (grammatical functions). JJ NN VBD JJ NN IN JJ NNS ◮ Hybrid representations may combine all elements. . Economic news had little effect on financial markets Introduction to Dependency Grammar 10(29) Introduction to Dependency Grammar 11(29) Introduction Introduction Some Theoretical Frameworks Some Theoretical Issues ◮ Word Grammar (WG) Hudson (1984, 1990) ◮ Dependency structure sufficient as well as necessary? ◮ Functional Generative Description (FGD) Sgall et al. (1986) ◮ Mono-stratal or multi-stratal syntactic representations? ◮ Dependency Unification Grammar (DUG) Hellwig (1986, 2003) ◮ What is the nature of lexical elements (nodes)? ◮ Meaning-Text Theory (MTT) Mel’ˇ ◮ Morphemes? cuk (1988) ◮ Word forms? ◮ (Weighted) Constraint Dependency Grammar ([W]CDG) ◮ Multi-word units? Maruyama (1990); Harper & Helzerman (1995); Menzel & Schr¨ oder ◮ What is the nature of dependency types (arc labels)? (1998); Schr¨ oder (2002) ◮ Grammatical functions? ◮ Functional Dependency Grammar (FDG) Tapanainen & J¨ arvinen ◮ Semantic roles? (1997); J¨ arvinen & Tapanainen (1998) ◮ What are the criteria for identifying heads and dependents? ◮ Topological/Extensible Dependency Grammar ([T/X]DG) ◮ What are the formal properties of dependency structures? Duchier & Debusmann (2001); Debusmann et al. (2004) Introduction to Dependency Grammar 12(29) Introduction to Dependency Grammar 13(29)
Introduction Introduction Capturing Adjuncts and Complements Criteria for Heads and Dependents ◮ Criteria for a syntactic relation between a head H and a There are two main kinds of dependencies for A → B: dependent D in a construction C Zwicky (1985); Hudson (1990) : ◮ Head-Complement: if A (the head) has a slot for B, then B is 1. H determines the syntactic category of C ; H can replace C . a complement 2. H determines the semantic category of C ; C specifies H . 3. H is obligatory; D may be optional. ◮ Head-Adjunct: if B has a slot for A (the head), then B is an 4. H selects D and determines whether D is obligatory. adjunct 5. The form of D depends on H (agreement or government). B is dependent on A in either case, but the selector is different 6. The linear position of D is specified with reference to H . ◮ Issues: ◮ The adjunct/complement distinction is captured in the type of ◮ Syntactic (and morphological) versus semantic criteria dependency relation and/or in the lexicon ◮ Exocentric versus endocentric constructions Introduction to Dependency Grammar 14(29) Introduction to Dependency Grammar 15(29) Introduction Introduction Some Clear Cases Some Tricky Cases Construction Head Dependent ◮ Complex verb groups (auxiliary ↔ main verb) Exocentric Verb Subject (sbj) ◮ Subordinate clauses (complementizer ↔ verb) Verb Object (obj) ◮ Coordination (coordinator ↔ conjuncts) Endocentric Verb Adverbial (vmod) ◮ Prepositional phrases (preposition ↔ nominal) Noun Attribute (nmod) ◮ Punctuation sbj obj nmod vmod nmod ? Economic news suddenly affected financial markets . I can see that they rely on this and that . Introduction to Dependency Grammar 16(29) Introduction to Dependency Grammar 17(29)
Introduction Introduction Some Tricky Cases Some Tricky Cases ◮ Complex verb groups (auxiliary ↔ main verb) ◮ Complex verb groups (auxiliary ↔ main verb) ◮ Subordinate clauses (complementizer ↔ verb) ◮ Subordinate clauses (complementizer ↔ verb) ◮ Coordination (coordinator ↔ conjuncts) ◮ Coordination (coordinator ↔ conjuncts) ◮ Prepositional phrases (preposition ↔ nominal) ◮ Prepositional phrases (preposition ↔ nominal) ◮ Punctuation ◮ Punctuation ? sbj sbj sbj sbj vg vg I can see that they rely on this and that . I can see that they rely on this and that . Introduction to Dependency Grammar 17(29) Introduction to Dependency Grammar 17(29) Introduction Introduction Some Tricky Cases Some Tricky Cases ◮ Complex verb groups (auxiliary ↔ main verb) ◮ Complex verb groups (auxiliary ↔ main verb) ◮ Subordinate clauses (complementizer ↔ verb) ◮ Subordinate clauses (complementizer ↔ verb) ◮ Coordination (coordinator ↔ conjuncts) ◮ Coordination (coordinator ↔ conjuncts) ◮ Prepositional phrases (preposition ↔ nominal) ◮ Prepositional phrases (preposition ↔ nominal) ◮ Punctuation ◮ Punctuation sbar sbar sbj obj sbj sbj obj sbj ? ? vg vg I can see that they rely on this and that . I can see that they rely on this and that . Introduction to Dependency Grammar 17(29) Introduction to Dependency Grammar 17(29)
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