linguistica generale e computazionale

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LINGUISTICA GENERALE E COMPUTAZIONALE. CONOSCENZA LESSICALE: IL LESSICO GENERATIVO. Introduction. Lexicon— ideally collection of all words of a language Information stored in a lexicon- Phonetic information pronunciation Semantic information meaning Morphological information - PowerPoint PPT Presentation

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  • LINGUISTICA GENERALE E COMPUTAZIONALECONOSCENZA LESSICALE: IL LESSICO GENERATIVO

  • *Introduction Lexicon ideally collection of all words of a language Information stored in a lexicon- Phonetic information pronunciation Semantic information meaning Morphological information transitivity and intransitivity (verbs) , count vs. mass (noun)

  • *Lexicon (contd) Example of eat in the Oxford Advanced Learners Dictionary eat /i:t/ v (pt ate /et/; pp eaten /i:tn/):1. sth (up) to food into the mouth,chew and swallow it: he was too ill to eat Lexical entryPronunciationMorphological informationMeaning

  • *Mental Lexicon Mental Lexicon: information stored in the mind of a native speaker Native speakers store information

    Phonetic information pronunciation Semantic information meaning Morphological information transitivity vs.intransitivity (verbs), count vs. mass (noun) Additional information use of a word in a new context, syntactic environment of a word, word-formation rules

  • *Example of Mental Lexicon Example of eat in a native speakers mind Pronunciation: long /i:/ is used in eat Grammatical information: past tense is ate /et/ Word-formation rules: /-s/ is the third person singular present tense marker as in he eats Meaning: 1. Take in solid food: she ate a banana 2. Take a meal: we did not eat until 10 P.M. 3. Worry or cause anxiety in a persistent way: whats eating you up. Syntactic Information: eat needs an agent to perform the action. the agent role is obligatory.

  • *Lexicon in Computational LinguisticsLexicon meant for Natural Language Processing (NLP) must have thefollowing properties:Morphological information Parts of speech information Rules should be there to deal with both regular and irregular forms e.g ate (past tense of eat) men (plural of man)Semantic informationCan handle lexical ambiguity Syntactic informationAction verbs will always have an agent

  • *Polysemy and the Logical Problem of PolysemyPolysemyAn individual word can have indefinite number of subtle meaning difference

    Natural Languages are highly polysemous

    This creates ambiguity

    Weinreich distinguishes between two types of ambiguityContrastive ambiguityComplementary polysemy

  • *Polysemy and the Logical Problem of Polysemy (contd)Contrastive AmbiguityA lexical item carries two distinct unrelated meaningsThis is a case of homonymy words spelled or pronounced in the same way but have different meaningsExample: bank a financial institution bank place beside a body of water.

  • (1)a. Mary doesnt believe the book. b. John sold his books to Mary.(2)a. Eno the cat is sitting on yesterdays newspaper. b. Yesterdays newspaper really got me upset.(3)a. Mary is in Harvard Square looking for the Bach sonatas. b. We wont get to the concert until after the Bach sonatas.(4)a. I have my lunch in the backpack. b. Your lunch was no longer today than it was yesterday.(5)a. The phone rang during my appointment. b. My next appointment is John.

    Complementary polysemy

  • *Polysemy and the Logical Problem of Polysemy (contd)Complementary PolysemyManifestation of the same basic senseSlightly different but related Example, John crawled through the window.The window is closed. Sense 1. ApparatusSense 2. Physical Object

  • *Sense Enumeration Lexicon (SEL)WordNet and similar resources are examples of SENSE ENUMERATION LEXICA

    Direct approach to handle polysemy is to allow the lexicon to have multiple listing of words, each annotated with a separate meaning or lexical sense.

    Widely accepted in both computational and theoretical linguistics.

  • *Sense Enumeration Lexicon (SEL)Example of Contrastive Senses bank1 CAT= count-noun GENUS= financial-institution bank2 CAT= count-noun GENUS= shore

  • *Nominal polysemy in sense enumeration lexicaNewspaper Newspaper2 CAT= count-noun GENUS= information

  • *Sense Enumeration Lexicon (SEL)Possible Modification of Complementary Polysemy in SELCAT= count-noun GENUS= informationCAT= count-noun GENUS= artefactsense1sense2newspaper

  • *Sense Enumeration Lexicon (SEL)Example of Complementary Polysemy Window2 CAT= count-noun GENUS= artifact

  • *Sense Enumeration Lexicon (SEL)Possible Modification of Complementary Polysemy in SELCAT= count-noun GENUS= artifactCAT= count-noun GENUS= apparatussense1sense2window

  • Syntactic polysemy deals with polivalency (I), object deletion (II) and the general properties of argument expression (III).

    (I) a. Mary began to read the novel. b. Mary began reading the novel. c. Mary began the novel.

    (II) a. Mary ate (her meal) quickly. b. Mary devoured *(her meal) quickly.

    (III) a. John carved a doll (out of the wood). b. John carved the wood (into a doll).

    Verbal polysemy in sense enumeration lexica

  • GENERATIVE LEXICON THEORY(Pustejovsky, 1991, 1995)Claim: the concepts associated with a word in a context are GENERATED by a process starting from lexical entries structured into QUALIA STRUCTUREs and involving GENERATIVE DEVICES such as TYPE COERCION and CO-COMPOSITION

  • *Generative lexicon theory: lexical entriesA lexical entry in the generative lexicon consists of the following elements at least:Argument StructureTrue ArgumentsDefault ArgumentsShadow ArgumentsTrue AdjunctsEvent StructureQualia StructureFormalConstitutiveTelicAgentive

  • *Argument StructureTrue Arguments: syntactically realized parameters of the lexical item John arrived late Default Arguments: logically present in the expressions but are not necessarily expressed syntactically.

    John built the house out of bricks True Adjuncts: modify the logical expression part of the situational interpretation She drove down to New York on Tuesday.

  • *Argument Structure (contd)Shadow Arguments: semantically incorporated in the lexical item and are expressed by discourse specification and contextual factors Mary buttered her toast hidden argument is the material being spread on the toast

    these are not optional arguments but expressible only under specific conditions

    refer to the semantic content that is not necessarily expressed in syntax

    Example: Mary buttered her toast with margarine

  • SELECTION1. a. The man fell/died. b. The rock fell/!died.

    a. John forced/!convinced the door to open.b. John forced/convinced the guests to leave.

    a. John poured milk into /!on his coffee.b. John poured milk into/on the bowl.

  • Integrating Selection into Grammars

  • CONSEQUENCE OF SELECTION: ONTOLOGICAL ASSUMPTIONS

  • BUT Unlike in other lexical theories, in GLT types can be modified via TYPE COERCION (see below)

  • *Event Structureevent type of a lexical item and a phrase events can be sub-classified into at least three sorts: State, Process and Transition Event Structure of build as found in the following expressions They are building a new house The house was built by John

    build

    EVENTSTR=E1= processE2= state

  • Word meaning is structured on the basis of four generative factors, called qualia roles, that capture how humans understand objects and relations in the world and provide the minimal explanation for the linguistic behavior of lexical items.

    FORMAL: the basic category that distinguishes an object within a larger domainCONSTITUTIVE: the relation between an object and its constituent partsTELIC: the objects purpose and functionAGENTIVE: factors involved in the objects origin or coming to being QUALIA ROLES

  • *Qualia structures and argument polysemy Qualia Structure for novel

  • *A generative device: type coercion Type Coerciona lexical item or phrase is coerced to a semantic interpretation by a governing item in the phrase, without changing its syntactic type

    Mary began to read the novel Mary began reading the novel Mary began the novel Function Application with Coercion different complement type of the verb different interpretations of the verb that arise for the different complements

  • *Other generative devicesSelective Bindinga lexical item or a phrase operates specifically on the substructure of a phrase, without changing the overall type in the composition a good knife: a knife that cuts well

    Co-compositionmultiple elements within a phrase behave as functors, generating new non-lexicalized senses for the words in composition John baked the potato John baked the cake

  • (i) The Generative Lexicon Theory proposes to separate the characteristicproperty (FORMAL role) from the functional aspect (TELIC role) of thenotion of food. Food is a concept making reference to distinct and orthogonal facets ofknowledge, each expressing a different explanation of this concept.

    We can represent our analytic knowledge associated with food by conjoining or unifying orthogonal values from and qualia roles.Such a structure is called a unified type.This method permits a general strategy for creating increasingly specificconcepts with conjunctive properties.

    (Unified types can be seen as structured by orthogonal dimensions orperspectives, rather than as inheriting properties from multiple parents in a homogeneous property structure.)

    EXAMPLE: FOOD

  • A schematic description of a lexical item a:

    a ARGSTR= ARG1= x

    QUALIA= CONST = what x is made of FORMAL = what x is TELIC = function of x AGENTIVE = how x came into being QUALIA ROLES

  • Schematic Representation

    food ARGSTR = [ARG 1 = x:substance]

    QUALIA = FORMAL = x TELIC = eat (e,y,x)

    Let PF and QT be the values associated with the FORMAL and TELIC qualia respectively and analyze the orthogonal values of the qualia roles as logical conjunction: x[PF(x) QT(x)].

    For the interpretation of the noun food, this would give the expression: x[substanceF (x) ye [eatT (e,y,x)]]

  • A dot object is a deeper structure relating the apparently contradictorysenses of the word. For each sense pair there is a relation that connectsthe senses in a well-defined way.

    The dot object is characterized as:- a Cartesian type product of n types (the product 1 x 2, of types 1 and 2, each denoting sets, is the ordered pair , where t1 1 , t2 2)with some additional constraints: there exists a relation R between the elements of 1 and 2 , namely, R(t1 , t2). This relation must be seen as part of the definition of the semantics for thedot object. NOMINAL POLYSEMY

  • Type combinations included in the broad range of complex typesencountered in natural language:

    a. phys_objinfo : e.g., book, record b. eventevent : e.g., construction, examinationc. eventquestion : e.g., examd. eventfood : e.g., lunch, dinnere. eventhuman : e.g., appointment

    For each of these type products, there is a unique relation, Ri, thatstructures the types.

    For example, nouns such as book or record, are structured by acontainment relation R (container-like concepts). This containment relation -hold(x,y)- must be encoded directly into thesemantics of the concept as the FORMAL quale value.

  • The lexical structure for newspaper as a dot object is represented as follows:

    newspaper ARGSTR = ARG1 = y:information ARG2 = x:phys_obj

    QUALIA = informationphys_obj FORM = hold(x,y) TELIC = read(e,w,xy) AGENT = write(e,v,xy)

    This translates to the following logical expression:x yev[newspaper (x:physobj y :info) hold(x,y) we [read (e,w,xy) [write(e;v,x y)]]

  • The lexical structure for book as a dot object is represented as follows:

    book ARGSTR = ARG1 = y:information ARG2 = x:phys_obj

    QUALIA = informationphys_obj FORM = hold(x,y) TELIC = read(e,w,xy) AGENT = write(e,v,xy)

    This translates to the following logical expression:x yev[book (x:physobj y :info) hold(x,y) we [read (e,w,xy) [write(e;v,x y)]]

  • MORE FORMAL DETAILS

  • Three Ranks of TypeEntitiesEvents

  • System of Generating Types

  • Qualia are incorporated into Type Itself

  • Qualia as Types

  • Functional Selection

  • Functional Type Coercion

  • Co-composition

  • Coercion in Function Composition

  • Selection and Coercion

  • Type Specification

  • GLT AND LEXICAL RESOURCES

  • *Generative lexicon vs. WordNetFormal role is similar to the hypernymy relationConstitutive role is similar to the meronymy relationNothing in WordNet like the functionality linkEvent structure Exists in some WordNets, e.g., Hindi WordNet

  • LEXICAL RESOURCES BASED ON GLTSIMPLELKB

  • SIMPLELessico creato allUniversita di Pisa

  • Concrete_entityAbstract_entityPropertyRepresentationTELICFurnitureInstrumentClothingArtworkSignLanguageInformation.....Living_entityHumanAnimalVegetal_entityArtifactSusbstanceLocationFoodMaterialQualityQuantityPhysical_propPsychol_prop.....ConventionCognitive_fact.....Artifactual_materialArtifactTOPAGENTIVECONSTITUTIVEENTITYEvent.........some semantic types for abstract & concrete entities

  • PhenomenonChangePsych_eventAspectualStateAct EVENTCause_changeRelational_stateNon_relational_actRelational_actMoveCause_actRelational_changeChange_possessionChange_locationAcquire_knowledgeNatural_transition...Creation..................Speech_act......some semantic types for events

  • some semantic types for adjectivesExtensionalIntensionalTOP

    Psychological_propSocial_propPhysical_propIntensifying_propTemporal_propRelational_propTemporalModalEmotiveMannerObject_relatedEmphasizer

  • E x t e n d e d E x t e n d e d r o l e s Q u a l i aS t r u c t u r e

  • Formal roleAgentive roleTelic roleConstitutive roleinstrumentis_aused_forcreated_byis_made_ofOrthogonal dimensions of meaning

  • Formal roleAgentive roleTelic roleConstitutive roleviolinOrthogonal dimensions of meaning

  • recipientedi legnofattoche serve per la conservazione e il trasportodi doghe arcuate tenute unite da cerchi di ferrodi liquidi, specialmente vinobottebarreltraditional dictionary definitionmeaning dimensions expressed by Qualia relations

  • REFERENCESPustejovsky, J. (1995). The generative Lexicon. Cambridge, MA: MIT Press.

  • ACKNOWLEDGMENTSSlides borrowed fromDebasri ChakrabartiJames PustejovskyNilda Ruimy

    ***********Dans le modle SIMPLE, la Extended Qualia Structure a t mise au point.Chacun des quatre roles subsume un ensemble de sous-types qui permettent une description plus fine et une caractrisation plus pointue de la nature des relations que les units smantiques entretiennent.Il est ainsi permis dindiquer non seulement fonction, origine et composition de lentit mais aussi de prciser le type de fonction, dorigine ou de composition ou la perspective dans laquelle on lenvisage. Quelques exemples du niveau de prcision en ce qui concerne la fonction, Lorigine, La composition

    Les rles formel et constitutif ainsi la relation dhypronymie, dantonymie ou de mronymie, sont exprims en rgle gnrale, par des relations intra-catgorielles et renseignent sur les affinits paradigmatiques des units lexicales

    Tandis que les rles agentif et tlique capturent des relations transversales existant entre units smantiques. Dans la description des noms tout au moins, ils sont reprsents par des relations inter-catgorielles et fournissent des informations de nature syntagmatique sur les diffrents prdicats qui contribuent clairer le sens dun mot.

    Voyons, dans une entre smantique, un exemple de qualia*At the encoding level, the adequacy of qualia roles for capturing key aspects of the lexical semantics of words, especially as far as nouns are concerned, results clearly from a parsing of traditional dictionary definitions. This example and the following one show that the meaning components which can be isolated in lexicographic definitions generally map quite easily on the dimensions expressed via qualia roles.