Computational Semantics Representation and Reasoning Frank Richter - PowerPoint PPT Presentation

Computational Semantics Representation and Reasoning Frank Richter Goethe Universität Frankfurt a.M. Institut für England- und Amerikastudien Abteilung Linguistik LACompLing2018, August 28–31 Stockholm University Frank Richter Computational Semantics: CLLRS August 31, 2018 1 / 33

Introduction L exical R esource S emantics: Semantics in HPSG overview of development and state of the C onstraint L anguage for L exical R esource S emantics informal discussion of relationship between LRS and its implementation as a component of TRALE CLLRS in a reasoning architecture Frank Richter Computational Semantics: CLLRS August 31, 2018 2 / 33

Grammar Specification in HPSG HPSG: Grammar = � Signature , Set of Principles � ◮ Signature: sort hierarchy, feature names, feature appropriateness, relation symbols and their arity ◮ Principles: implicational statements (Head Feature Principle, Subcategorization Principle, ID Principle,. . . ) Model theoretic interpretation of grammars: Linguistic expressions are structures ‘denoted’ by the grammar Locality assumption about principles: local ‘trees’ (or within a node) Consequences for semantics: ◮ Semantic composition specified in the feature logic ◮ Logical representations in the denotation of the grammar ◮ For one sentence, several logical expressions might be possible solutions to the set of constraints imposed by the set of semantic principles Frank Richter Computational Semantics: CLLRS August 31, 2018 3 / 33

HOL Representations in HPSG (idealized) Frank Richter Computational Semantics: CLLRS August 31, 2018 4 / 33

HOL Representations in HPSG (extensional) Frank Richter Computational Semantics: CLLRS August 31, 2018 5 / 33

Lexical Resource Semantics (LRS) Semantic representations from a typed logic 1 ◮ functional type theory with types e , s , and t ◮ lambda abstraction, function application, and equality Semantic composition by relations between lexical term 2 contributions ( semantic constraints; underspecification ) Central semantic composition concepts: 3 ◮ semantic term contributions (semantic resources), PARTS ◮ external content: EXCONT ◮ internal content: INCONT ◮ subterm relationships ( α ⊳ β ) Local semantics: 4 ◮ main content: MAIN ◮ discourse referent: DR Frank Richter Computational Semantics: CLLRS August 31, 2018 6 / 33

Words: Proper Name A proper name: Elvis  word  � � elvis PHON     � �  elvis ′  DR   SYNSEM LOC CONT   MAIN elvis ′         lrs     EXCONT me      SEM    INCONT elvis ′         � elvis ′ � PARTS [ SEM elvis ′ ] SEM value in linear notation: ˆ [ { elvis ′ } ] In more detail: Frank Richter Computational Semantics: CLLRS August 31, 2018 7 / 33

Words: Proper Name A proper name: Elvis  word  � � elvis PHON     � �  elvis ′  DR   SYNSEM LOC CONT   MAIN elvis ′         lrs     EXCONT me      SEM    INCONT elvis ′         � elvis ′ � PARTS [ SEM elvis ′ ] SEM value in linear notation: ˆ [ { elvis ′ } ] In more detail: Frank Richter Computational Semantics: CLLRS August 31, 2018 7 / 33

Words: Count Noun A count noun (here: � e , t � ): clown  word  � � clown PHON     � �   X DR   SYNSEM LOC CONT   MAIN clown ′   & 1 ⊳ α      lrs      EXCONT quantifier( X , α, β )      SEM    1 clown ′ ( X )     INCONT     � clown ′ ( X ), clown ′ � PARTS [ SEM quantifier( x , _clown ′ ( x )_ , _) ] Informally, in linear notation: In more detail: ˆ − quantifier( x , [{clown ′ ( x )}] , _) Frank Richter Computational Semantics: CLLRS August 31, 2018 8 / 33

Words: Count Noun A count noun (here: � e , t � ): clown  word  � � clown PHON     � �   X DR   SYNSEM LOC CONT   MAIN clown ′   & 1 ⊳ α      lrs      EXCONT quantifier( X , α, β )      SEM    1 clown ′ ( X )     INCONT     � clown ′ ( X ), clown ′ � PARTS [ SEM quantifier( x , _clown ′ ( x )_ , _) ] Informally, in linear notation: In more detail: ˆ − quantifier( x , [{clown ′ ( x )}] , _) Frank Richter Computational Semantics: CLLRS August 31, 2018 8 / 33

Basic Principles 1 LRS P ROJECTION P RINCIPLE : In each phrase , 1. the EXCONT values of the head and the mother are identical, � sem excont � 1 phrase → h-dtr sem excont 1 phrase *> (sem: @sem([ˆX]), hdtr:sem: @sem([ˆX])). 2. the INCONT values of the head and the mother are identical, � sem incont � 1 phrase → h-dtr sem incont 1 phrase *> (sem: @sem([{X}]), hdtr:sem: @sem([{X}])). Frank Richter Computational Semantics: CLLRS August 31, 2018 9 / 33

Basic Principles 2 3. the PARTS value contains all and only the elements of the PARTS values of the daughters.     sem parts 1  ∧ append ( 2 , 3 , 1 ) phrase → h-dtr sem parts 2    nh-dtr sem parts 3 phrase *> (sem: @sem([X,Y]), hdtr:sem: @sem(X), nh_dtr:sem: @sem(Y)). Frank Richter Computational Semantics: CLLRS August 31, 2018 10 / 33

From the Semantics Principle (1) S EMANTICS P RINCIPLE (clause for Det + N ′ ): If the non-head is a quantificational determiner then its INCONT value is of the form quantifier ( x , ρ, ν ) , the INCONT value of the head is a component of ρ , and the INCONT value of the non-head daughter is identical with the EXCONT value of the head daughter � � � cat head � det → nh-dtr ss loc cont main quantifier   � excont �   1 h-dtr sem   incont 2     ∧  2 ⊳ 3    � �  � quantifier �       nh-dtr sem incont 1  restr 3 Frank Richter Computational Semantics: CLLRS August 31, 2018 11 / 33

From the Semantics Principle (1, continued) � � � cat head � det → nh-dtr ss loc cont main quantifier   � excont �   1 h-dtr sem   incont 2     ∧  2 ⊳ 3    � �   � quantifier �      nh-dtr sem incont 1  restr 3 (phrase, nh_dtr:synsem:loc:(cat:head:det, cont:main:@sem(quantifier)) *> (nh_dtr:sem: (@sem([{quantifier(x,[Two],_)}]), @sem([{One}]) ), hdtr:sem: @sem([ˆOne:[{Two}]]) ). Frank Richter Computational Semantics: CLLRS August 31, 2018 12 / 33

Local Semantic Projection Local semantic values are inherited along syntactic head paths: � �   DR 1 SS LOC CONT MAIN 2   � � →   headed_phrase   � � 1  DR  H - DTR SS LOC CONT   MAIN 2 Frank Richter Computational Semantics: CLLRS August 31, 2018 13 / 33

A Noun Phrase in LRS Notation NP � dr �  x  ss loc content 3a clown ′ main       4 3 ( x, γ, δ ) exc     semantics inc 3     � 4 , 4a , 3 , 3a � ps & 3 ⊳ γ comp head Det N � dr � � dr �  x   x  ss loc content ss loc content main 3 main 3a             exc 4 exc 4         4 3 ( x , γ, δ ) 3 clown ′ ( x ) semantics inc semantics inc         � 4 , 4a x � � 3 , 3a clown ′ � ps ps three clowns Frank Richter Computational Semantics: CLLRS August 31, 2018 14 / 33

Basic Principles 3 The I NCONT P RINCIPLE : In each lrs , the INCONT value is an element of the PARTS list and a component of the EXCONT value.     excont 1 lrs →  ∧ member ( 2 , 3 ) ∧ 2 ⊳ 1 incont 2    parts 3 Frank Richter Computational Semantics: CLLRS August 31, 2018 15 / 33

Basic Principles 4 The E XCONT P RINCIPLE : Clause (a): In every phrase, the EXCONT value of the non-head daughter is an element of the non-head daughter’s PARTS list. � � � � � excont � 1 phrase → ∧ member ( 1 , 2 ) nh-dtr sem parts 2 Clause (b): In every utterance, every subexpression of the EXCONT value of the utterance is an element of its PARTS list, and every element of the utterance’s PARTS list is a subexpression of the EXCONT value. u-sign →   � � � � excont � � 1 ∧ 3 ⊳ 1 ∧ member ( 4 , 2 ) → sem   ∀ 1 ∀ 2 ∀ 3 ∀ 4 parts 2     ( member ( 3 , 2 ) ∧ 4 ⊳ 1 ) Frank Richter Computational Semantics: CLLRS August 31, 2018 16 / 33