【正文】 ↑ =↓ (↑OBJ) = ↓ NP (↑NUM) = SG (↑PRED) = ‘GIRL’ N (↑TENSE) = PAST (↑PRED) = ‘HAND’ V (↑SPEC) = A (↑NUM) = SG DET (↑OBJ) = ↓ NP (↑SPEC) = ↓ DET (↑NUM) = SG (↑PRED) = BABY N (↑SPEC) = ↓ (↑NUM) = SG DET (↑NUM) = SG (↑PRED) = TOY N a girl handed f1 f2 f4 f5 f3 (f4 SPEC) = THE (f4 NUM) = SG (f4 PRED) = ?BABY? (f3 TENSE) = past (f2 SPEC) = A (f2 NUM) = SG (f2 NUM) = SG (f2 PRED) = ?GIRL? Etc. f1= f3 (f1 SUBJ) = f2 10/18/2021 LexicalFunctional Grammars FDescription to FStructure ? Locate Operator ? Obtain value for designator ? Merge Operator (*Unify*) ? If left and right values exist, check if values are equal ? Else, create new entity (if properties are patible) ? Similar to taking the union of two sets (if conflicts don?t exist) ? Start clean。LexicalFunctional Grammar A Formal System for Grammatical Representation Kaplan and Bresnan, 1982 Erin Fitzgerald NLP Reading Group October 18, 2021 10/18/2021 LexicalFunctional Grammars LFG History ? Developed by J. Bresnan and R. Kaplan in early 1970?s ?Believed Chomskyan approach doesn?t model psychological reality of language ? Other motivations: ? Supported in wider variety of languages than other formalisms (ex nonconfigurational languages with ~free word order/ case marks) ? Movement paradoxes: ? That he was sick we talked about __ for days. ? *We talked about that he was sick for days. ? We talked about the fact that he was sick for days. “Syntax is not just structurebased” 10/18/2021 LexicalFunctional Grammars How it’s different from Chomsky X’ ? Requires a higher level of mathematical precision ? Subject, Object, etc considered primitives, not defined from positions in tree ? Empty categories and funct. projections avoided ? No movement ? Unificationbased ? Levels of representation not strictly derived from each other ? Not assumed that phonological, etc contents are derived from syntactic structure in any way. 10/18/2021 LexicalFunctional Grammars How it’s different from HPSG ? No hierarchical classification to deal with vertical and horizontal redundancy ? LFG focuses on the processing and psychological reality of language ? HPSG bines all syntactic, phonological, etc information into a single level 10/18/2021 LexicalFunctional Grammars Generative Power of LFG ? Not as powerful as general rewriting system or Turing Machine (LF languages are contextsensitive) ? But, greater generative capacity than CFG (lower bound) ? Allows anbn, ωω nonCF languages ? Sources of generative power: ? Functional Composition: Helps encode range of tree properties ? Equality Predicate: Enforces a match between properties encoded from different nodes 10/18/2021 LexicalFunctional Grammars Correspondence Between Levels ? C(onstituent)structure: varies across languages ? F(unctional)structure: Universal properties ?Structures aren?t isomorphic, but related by different correspondences string cstructure fstructure discourse structure semantic structure φ σ π δ ? 10/18/2021 LexicalFunctional Grammars CStructure ? Composed of ? Terminal strings ? Syntactic categories ? Dominance/precedence relations ? Expressed through phrase structure trees ? Determined by CF phrase structure rules ?Regulated by a version of X? theory 10/18/2021 LexicalFunctional Grammars CStructure S NP VP DET N NP V N DET DET N NP a girl handed the baby a toy S ? NP VP (↑SUBJ)=↓ ↑ =↓ NP ? DET N VP ? V NP NP (↑ OBJ)=↓ (↑ OBJ2)=↓ Immediate Domination Metavariables: ↑ : mother fstructure ↓ : self fstructure . head Set specifiers: S ? S CONJ S ↓?↑ ↓?↑ Adjuncts also use set indicators 10/18/2021 LexicalFunctional Grammars Fstructure ? Composed of ? Grammatical