Grammatical Relations and Lexical Functional Grammar Grammar Formalisms Spring Term 2004
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Grammatical Relations and Lexical Functional Grammar Grammar Formalisms Spring Term 2004 Grammatical Relations • Subject – Sam ate a sandwich. – A sandwich was eaten by Sam. • Direct object – Sam ate a sandwich. – Sue gave Sam a book. – Sue gave a book to Sam. • Others that we will define later Grammatical Relations in Grammar Formalisms • Tree Adjoining Grammar: – Subject is defined structurally: first NP daughter under S – Object is defined structurally: NP that is a sister to V – But TAG output can be mapped to a dependency grammar tree that includes subject and object. • Categorial Grammar: – Grammatical relations are defined structurally if at all. • Head Driven Phrase Structure Grammar: – Subject is defined indirectly as the first element on the verb’s subcategorization list. • Lexical Functional Grammar: – Grammatical relations are labelled explicitly in a feature structure. Motivation for Grammatical Relations: Subject-Verb Agreement – – – – Sam likes sandwiches. *Sam like sandwiches. The boys like sandwiches. *The boys likes sandwiches. • Hypothesis 1: The verb agrees with the agent. • Hypothesis 2: The verb agrees with the first NP. • Hypothesis 3: The verb agrees with the NP that is a sister of VP. • Hypothesis 4: The verb agrees with the subject. – Vacuous unless we have a definition or test for subjecthood. Checking the hypotheses • Hypothesis 1: – Can you think of a counterexample in English.? • Hypothesis 2: – Can you think of a counterexample in English? – Can you think of a counterexample in another language that has subject-verb agreeement? • (not Japanese or Chinese) Some differences between English and Warlpiri (Australia) S VP’ NP VP Aux The two small children V NP are chasing that dog. S NP Wita-jarra-rlu Small-DU-ERG AUX V NP NP NP ka-pala wajili-pi-nyi yalumpu kurdu-jarra-rlu maliki. pres-3duSUBJ chase-NPAST that.ABS child-DU-ERG dog.ABS Some Definitions • Case marking: different word form depending on the grammatical relation: – – – – She ate a sandwich. (nominative case marking: subject) *Her ate a sandwich. Sam saw her. (accusative or objective case marking: object) *Sam saw she. • Ergative case marking: – Marks the subject, but only if the verb is transitive (has a direct object). • Absolutive case marking: – Marks the subject, but only if the verb is intransitive. – Also marks the direct object. • English has nominative and accusative case markers on pronouns. • English does not have ergative or absolutive case marking. Possible word orders in Warlpiri that are not possible in English • *The two small are chasing that children dog. • *The two small are dog chasing that children. • *Chasing are the two small that dog children. • *That are children chasing the two small dog. Checking the hypotheses • Hypothesis 2: – Does it work for Warlpiri? • Hypothesis 3: – Does it work for Warlpiri? English and Warlpiri Under Hypothesis 3 S Deep structure VP’ NP VP Aux V NP English S Surface Structure VP’ NP VP Aux V NP English and Warlpiri under Hypothesis 3 S VP’ VP NP Aux Warlpiri V Deep structure NP S NP S AUX S S NP NP S Surface Structure VP’ NP VP Aux e ee V NP e English and Warlpiri under Hypothesis 3 S VP’ VP NP Aux Warlpiri V S NP Deep structure NP Adjunctions: represent the real word order S AUX S S NP Remnants of the original tree represent gramamtical relations NP S VP’ NP VP Aux V NP e ee Empty categories: represent semantic roles Surface Structure e English and Warlpiri under Hypothesis 4 Constituent structure: represents word order and grouping of words into constituents English S Subject VP’ NP VP Aux Warlpiri NP V V NP NP NP “two small children” Predicate chase agent theme Object “that dog” NP S Aux Functional structure: represents grammatical relations and semantic roles English and Warlpiri under Hypothesis 4 Constituent structure: represents word order and grouping of words into constituents English S Subject VP’ NP VP Aux Warlpiri NP V V NP chase agent theme Object “that dog” NP NP NP “two small children” Predicate Mapping from c-structure to fstructure S Aux Functional structure: represents gramamtical relations and semantic roles English and Warlpiri under Hypothesis 4 Constituent structure: represents word order and grouping of words into constituents English S Subject VP’ NP VP Aux V NP S Aux V NP NP NP “two small children” Predicate chase agent theme Object “that dog” NP Mapping from c-structure to f-structure Warlpiri Functional structure: represents gramamtical relations and semantic roles Keeping Score Hypothesis 3: • One structure contains a mish-mash of word order, constituency, grammatical relations, and thematic roles • Adjunctions • Empty categories and invisible constituents Hypothesis 4: • Need an extra data structure for grammatical relations and semantic roles • Need a mapping between c-structure and f-structure • Need a reproducible, falsifiable definition of grammatical relations. Levels of Representation in LFG [s [np The bear] [vp ate [np a sandwich]]] SUBJ Agent Eat < agent SUBJ PRED SUBJ OBJ eat functional structure Lexical mapping thematic roles patient patient > lexical mapping OBJ S NP constituent structure Grammatical encoding VP VP V NP OBJ V PP OBL Grammatical Encoding For English!!! A surprise • Syntax is not about the form (phrase structure) of sentences. • It is about how strings of words are associated with their semantic roles. – Phrase structure is only part of the solution. • Sam saw Sue – Sam: perceiver – Sue: perceived Surprise (continued) • Syntax is also about how to tell that two sentences are thematic paraphrases of each other (same phrases filling the same semantic roles). – It seems that Sam ate the sandwich. – It seems that the sandwich was eaten by Sam. – Sam seems to have eaten the sandwich. – The sandwich seems to have been eaten by Sam. How to associate phrases with their semantic roles in LFG • Starting from a constituent structure tree: • Grammatical encoding tells you how to find the subject. – The bear is the subject. • Lexical mapping tells you what semantic role the subject has. – The subject is the agent. – Therefore, the bear is the agent. Levels of Representation in LFG [s [np The sandwich ] [vp was eaten [pp by the bear]]] constituent structure Grammatical encoding SUBJ PRED OBL patient eat agent Eat < agent OBL patient > SUBJ lexical mapping SUBJ S NP functional structure Lexical mapping thematic roles VP VP V NP OBJ V PP OBL Grammatical Encoding For English!!! Active and Passive • Active: – Patient is mapped to OBJ in lexical mapping. • Passive – Patient is mapped to SUBJ in lexical mapping. • Notice that the grammatical encodings are the same for active and passive sentences!!! Passive mappings • Starting from the constituent structure tree. • The grammatical encoding tells you that the sandwich is the subject. • The lexical mapping tells you that the subject is the patient. – Therefore, the sandwich is the patient. • The grammatical encoding tells you that the bear is oblique. • The lexical mapping tells you that the oblique is the agent. – Therefore, the bear is the agent. How you know that the active and passive have the same meaning • In both sentences, the mappings connect the bear to the agent role. • In both sentences, the mappings connect the sandwich to the patient role (roll?) • In both sentences, the verb is eat. Levels of Representation in LFG [s-bar [np what ] [s did [np the bear] eat ]] constituent structure Grammatical encoding OBJ SUBJ patient Eat < agent SUBJ S-bar NP S OBJ agent patient > PRED eat functional structure Lexical mapping thematic roles lexical mapping OBJ VP S NP SUBJ V PP OBL Grammatical Encoding For English!!! Wh-question • Different grammatical encoding: – In this example, the OBJ is encoded as the NP immediately dominated by S-bar • Same lexical mappings are used for: – What did the bear eat? – The bear ate the sandwich. Functional Structure SUBJ PRED TENSE OBJ PRED ‘bear’ NUM sg PERS 3 DEF + ‘eat< agent patient > SUBJ OBJ past PRED ‘sandwich’ NUM sg PERS 3 DEF - Functional Structure • Pairs of attributes (features) and values – Attributes (in this example): SUBJ, PRED, OBJ, NUM, PERS, DEF, TENSE – Values: • Atomic: sg, past, +, etc. • Feature structure: [num sg, pred `bear’, def +, person 3] • Semantic form: ‘eat<subj ob>’, ‘bear’, ‘sandwich’ Semantic Forms • Why are they values of a feature called PRED? – In some approaches to semantics, even nouns like bear are predicates (function) that take one argument and returns true or false. – Bear(x) is true when the variable x is bound to a bear. – Bear(x) is false when x is not bound to a bear. Why is it called a Functional Structure? X squared 1 1 2 4 3 9 Each feature has a unique value. Also, another term for grammtical relation is grammatical function. 4 16 5 features 25 values We will use the terms functional structure, f-structure and feature structure interchangeably. Give a name to each function f1 SUBJ PRED ‘bear’ NUM sg f2 PERS 3 DEF + PRED ‘eat< agent patient > SUBJ OBJ TENSE past OBJ PRED ‘sandwich’ NUM sg f3 PERS 3 DEF - How to describe an f-structure • F1(TENSE) = past – Function f1 applied to TENSE gives the value past. • F1(SUBJ) = [PRED ‘bear’, NUM sg, PERS 3, DEF +] • F2(NUM) = sg Descriptions can be true or false • F(a) = v – Is true if the feature-value pair [a v] is in f. – Is false if the feature-value pair [a v] is not in f. This is the notation we really use • (f1 TENSE) = past • Read it this way: f1’s tense is past. • (f1 SUBJ) = [PRED ‘bear’, NUM sg, PERS 3, DEF +] • (f2 NUM) = sg Chains of function application • (f1 SUBJ) = f2 • (f2 NUM) = sg • ((f1 SUBJ) NUM) = sg • Write it this way. (f1 SUBJ NUM) = sg • Read it this way. “f1’s subject’s number is sg.” More f-descriptions • (f a) = v – f is something that evaluates to a function. – a is something that evaluates to an attribute. – v is something that evaluates to a function, symbol, or semantic form. • (f1 subj) = (f1 xcomp subj) – Used for matrix coding as subject. A subject is shared by the main clause and the complement clause (xcomp). • (f1 (f6 case)) = f6 – Used for obliques SUBJ PRED TENSE VFORM XCOMP S NP N VP V PRED ‘lion’ NUM pl PERS 3 ‘seem < theme > SUBJ’ XCOMP pres fin SUBJ [ ] VFORM INF PRED ‘live< theme loc >’ VP-bar SUBJ OBL-loc COMP VP V PP P NP DET N Lions seem to live in the forest CASE PRED OBJ OBL-loc OBJ OBL-loc ‘in<OBJ>’ PRED ‘forest’ NUM sg PERS 3 DEF + SUBJ f1 f2 PRED TENSE VFORM XCOMP S n1 n2 NP n3 N VP V n5 n4 VP-bar SUBJ n6 f4 n7 COMP VP PRED ‘lion’ NUM pl PERS 3 ‘seem < theme > SUBJ’ XCOMP pres fin SUBJ [ ] f3 VFORM INF PRED ‘live< theme loc >’ OBL-loc n8 f5 V PP n9 P n10 NP n11 DET N n12 n13 n14 Lions seem to live in the forest CASE PRED OBJ f6 OBL-loc OBJ OBL-loc ‘in<OBJ>’ PRED ‘forest’ NUM sg PERS 3 DEF + SUBJ f1 f2 PRED TENSE VFORM XCOMP S n1 n2 NP n3 N VP V n5 n4 VP-bar SUBJ n6 f4 n7 COMP VP PRED ‘lion’ NUM pl PERS 3 ‘seem < theme > SUBJ’ XCOMP pres fin SUBJ [ ] f3 VFORM INF PRED ‘live< theme loc >’ OBL-loc n8 f5 V PP n9 P n10 NP n11 DET N n12 n13 n14 Lions seem to live in the forest CASE PRED OBJ f6 OBL-loc OBJ OBL-loc ‘in<OBJ>’ PRED ‘forest’ NUM sg PERS 3 DEF +
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