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Grammatical Relations and Lexical Functional Grammar Grammar Formalisms Spring Term 2004.

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Presentation on theme: "Grammatical Relations and Lexical Functional Grammar Grammar Formalisms Spring Term 2004."— Presentation transcript:

1 Grammatical Relations and Lexical Functional Grammar Grammar Formalisms Spring Term 2004

2 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

3 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.

4 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.

5 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)

6 Some differences between English and Warlpiri (Australia) The two small children are chasing that dog. Aux V NP NP VP VP’ S Wita-jarra-rlu ka-pala wajili-pi-nyi yalumpu kurdu-jarra-rlu maliki. Small- DU-ERG pres- 3duSUBJ chase- NPAST that.ABS child- DU-ERG dog.ABS NP AUX V NP NP NP S

7 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.

8 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.

9 Checking the hypotheses Hypothesis 2: –Does it work for Warlpiri? Hypothesis 3: –Does it work for Warlpiri?

10 English and Warlpiri Under Hypothesis 3 NP VP VP’ S Aux V NP Deep structure NP VP VP’ S Aux V NP Surface Structure English

11 English and Warlpiri under Hypothesis 3 NP VP’ S Aux V NP Deep structure Surface Structure Warlpiri VP NP VP VP’ NP S Aux V NP S NP AUX S NP S S e e e e

12 English and Warlpiri under Hypothesis 3 NP VP’ S Aux V NP Deep structure Surface Structure Warlpiri VP NP VP VP’ NP S Aux V NP S NP AUX S NP S S e e e Empty categories: represent semantic roles Adjunctions: represent the real word order Remnants of the original tree represent gramamtical relations e

13 English and Warlpiri under Hypothesis 4 NP VP VP’ S Aux V NP English Warlpiri S NP Aux V NP NP NP Constituent structure: represents word order and grouping of words into constituents Functional structure: represents grammatical relations and semantic roles Subject “two small children” Predicate chase agent theme Object “that dog”

14 English and Warlpiri under Hypothesis 4 NP VP VP’ S Aux V NP English Warlpiri S NP Aux V NP NP NP Constituent structure: represents word order and grouping of words into constituents Functional structure: represents gramamtical relations and semantic roles Subject “two small children” Predicate chase agent theme Object “that dog” Mapping from c-structure to f- structure

15 English and Warlpiri under Hypothesis 4 NP VP VP’ S Aux V NP English Warlpiri S NP Aux V NP NP NP Constituent structure: represents word order and grouping of words into constituents Functional structure: represents gramamtical relations and semantic roles Subject “two small children” Predicate chase agent theme Object “that dog” Mapping from c-structure to f-structure

16 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.

17 Levels of Representation in LFG [ s [ np The bear] [ vp ate [ np a sandwich]]] constituent structure SUBJ PRED OBJ functional structure Agent eat patient thematic roles Grammatical encoding Lexical mapping Eat lexical mapping SUBJ OBJ S NP SUBJ VP V NP OBJ VP V PP OBL Grammatical Encoding For English!!!

18 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

19 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.

20 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.

21 Levels of Representation in LFG [ s [ np The sandwich ] [ vp was eaten [ pp by the bear]]] constituent structure SUBJ PRED OBL functional structure patient eat agent thematic roles Grammatical encoding Lexical mapping Eat lexical mapping OBL SUBJ S NP SUBJ VP V NP OBJ VP V PP OBL Grammatical Encoding For English!!!

22 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!!!

23 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.

24 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.

25 Levels of Representation in LFG [s-bar [ np what ] [s did [ np the bear] eat ]] constituent structure OBJ SUBJ PRED functional structure patient agent eat thematic roles Grammatical encoding Lexical mapping Eat lexical mapping SUBJ OBJ VP V PP OBL Grammatical Encoding For English!!! S NP SUBJ S-bar NP OBJ S

26 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.

27 Functional Structure SUBJ PRED ‘bear’ NUM sg PERS 3 DEF + PRED ‘eat SUBJ OBJ TENSE past OBJ PRED ‘sandwich’ NUM sg PERS 3 DEF -

28 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 ’, ‘bear’, ‘sandwich’

29 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.

30 Why is it called a Functional Structure? X squared Each feature has a unique value. featuresvalues Also, another term for grammtical relation is grammatical function.

31 We will use the terms functional structure, f-structure and feature structure interchangeably.

32 Give a name to each function SUBJ PRED ‘bear’ NUM sg PERS 3 DEF + PRED ‘eat SUBJ OBJ TENSE past OBJ PRED ‘sandwich’ NUM sg PERS 3 DEF - f1 f2 f3

33 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

34 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.

35 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

36 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.”

37 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

38 Lions seem to live in the forest DET N P NP V PP COMP VP N V VP-bar NP VP S SUBJ PRED ‘lion’ NUM pl PERS 3 PRED ‘seem SUBJ’ XCOMP TENSE pres VFORM fin XCOMP SUBJ [ ] VFORM INF PRED ‘live ’ SUBJ OBL-loc OBJ OBL -loc CASE OBL-loc PRED ‘in ’ OBJ PRED ‘forest’ NUM sg PERS 3 DEF +

39 Lions seem to live in the forest DET N P NP V PP COMP VP N V VP-bar NP VP S SUBJ PRED ‘lion’ NUM pl PERS 3 PRED ‘seem SUBJ’ XCOMP TENSE pres VFORM fin XCOMP SUBJ [ ] VFORM INF PRED ‘live ’ SUBJ OBL-loc OBJ OBL -loc CASE OBL-loc PRED ‘in ’ OBJ PRED ‘forest’ NUM sg PERS 3 DEF + f1 f3 f2 f4 f5 f6 n7 n6 n5 n4 n3 n2 n1 n10 n9 n8 n11 n13 n12 n14

40 Lions seem to live in the forest DET N P NP V PP COMP VP N V VP-bar NP VP S SUBJ PRED ‘lion’ NUM pl PERS 3 PRED ‘seem SUBJ’ XCOMP TENSE pres VFORM fin XCOMP SUBJ [ ] VFORM INF PRED ‘live ’ SUBJ OBL-loc OBJ OBL -loc CASE OBL-loc PRED ‘in ’ OBJ PRED ‘forest’ NUM sg PERS 3 DEF + f1 f3 f2 f4 f5 f6 n7 n6 n5 n4 n3 n2 n1 n10 n9 n8 n11 n13 n12 n14


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