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September 17, 2007 11-721: Grammars and Lexicons Lori Levin Summary of English Noun Phrases • There is a kind of constituent (an N-bar) that you probably didn’t know was there. – The methodology of using tests for constituency lead to this discovery. – This is an advantage of a precise methodology; it leads you to discover things. • Phrases have heads. • The heads are surrounded by layers of modifiers. – Innermost layer: complements/arguments – Second layer (recursive): adjuncts – Outermost layer: specifiers Heads • The head determines the properties of the whole phrase. – The child’s book is on the table. • Singular head, singular NP. – The children’s book is on the table. • Singular head, singular NP. • The number of the possessor doesn’t matter. – The child’s books are on the table. • Plural head, plural NP. • Important for grammar writing. – Features need to be passed up from the head. • Important for dependency parsing. Structure and Function • Grammar is about function as well as structure. • Grammar is about the mapping between structure and function. The Functions of NPs • Grammatical Functions: – Subject and object • Semantic Roles: – Agent and patient • Pragmatic Roles: – Old and new information Functions of NPs • What did the kids eat? They ate some chocolate. – Typical sentence: • Subject=agent=old information • Also typical because the subject is animate and definite and the object is inanimate and indefinite. • If all sentences were like this, syntacticians could retire. Functions of NPs • Some chocolate was eaten by the kids – The subject is not the agent. • Who ate the chocolate? The kids ate the chocolate? – Subject is new information. Semantic Roles • • • • Sam opened the door with a key. They key opened the door. The door was opened by Sam with a key. The door opened (with a key). • Sam bought a book from Sue. • Sue sold a book to Sam. Predicates and Arguments • Verbs (and sometimes nouns and adjectives) describe events, states, and relations that have a certain number of participants. – The children devoured the spaghetti. • Two participants – The teacher handed the book to the student. • Three particpants. – Problems exist. • One participant. • The participants are referred to as arguments of the verb. (Like arguments of a function.) Valency and Subcategorization • Fillmore and Kay, Lecture Notes, Chapter 4: – The children devoured the spaghetti. – *The children devoured. – *The children devoured the spaghetti the cheese. – She handed the baby a toy. – *She handed the baby. – *She handed the toy. – Problems exist. – *Problems exist more problems. Valency • The number of participants is called the verb’s valence or valency. – Devour has a valency of two. – Hand has a valency of three. – Exist has a valency of one. • Linguists took this term from chemistry – how many electrons are missing from the outer shell. – The first linguist to use the term was Charles Hockett in the 1950’s. Subcategorization • Verbs are divided into subcategories that have different valencies. • Here is how the terminology works: – Exist, devour, and hand have different subcategorizations • i.e., They are in different subcategories – Devour subcategorizes for a subject and a direct object. – Devour is subcategorized for a subject and a direct object. – Devour takes two arguments, a subject and a direct object (or an agent and a patient). Arguments are not always Noun Phrases • The italicized phrases are also arguments: – He looked very pale. • Adjective Phrase – The solution turned red. • Adjective Phrase – I want to go. • Verb Phrase – He started singing a song. • Verb Phrase – We drove to New York. • Prepositional Phrase Optional and Obligatory Arguments • The direct object of eat is optional: – The children ate. – The children ate cake. • The direct object of devour is not optional: – *The children devoured. – The children devoured the cake. Optional Arguments • The dog ran. • The dog ran from the house to the creek through the garden along the path. Optional vs. Invisible Arguments a. What happened to the cake? b. The children ate. b’. The children ate it. In English, Sentences b and b’ do not mean the same thing in this context. Compare to Japanese and Chinese. Adjuncts • Locations, times, manners, and other things that can go with almost any sentences are called adjuncts. – The children ate the cake quickly at 2:00 in the kitchen. How to tell arguments from adjuncts • There are some general guidelines that are not always conclusive. • Adjuncts are always optional. – but some arguments are optional too • Repeatability: – The children devoured the cake at 2:00 on Monday. • Two temporal adjuncts – The children devoured the cake in Pittsburgh in a restaurant. • Two locative adjuncts – *The children devoured the cake the dessert. • arguments are not repeatable Semantic Roles: Motivation • The verb open appears in different subcategorization patterns: – Sam opened the door with a key. – The key opened the door. – The door was opened by Sam with a key. – Sam’s opening of the door with a key • How can we represent the meanings of these sentences in a way that shows that they are related? Semantic Roles: Motivation • These sentences do not have the same meaning even though they have the same verb: – Sam interviewed Sue. – Sue interviewed Sam. Semantic Roles: Motivation These sentences mean roughly the same thing even though they use different verbs: • Sam bought a toy from Sue. • Sue sold a toy to Sam. Semantic role names – Sam opened the door with a key. – The key opened the door. – The door was opened by Sam with a key. – Sam’s opening of the door with a key • Open – Agent: Sam – Patient: door – Instrument: key Semantic Roles Names • These sentences do not have the same meaning: – Sam interviewed Sue. – Sue interviewed Sam. • Interview – Agent: Sam – Patient: Sue • Interview – Agent: Sue – Patient: Sam Examples of Semantic Roles • Agent: an agent acts volitionally or intentionally – The students worked. – Sue baked a cake. Examples of Semantic Roles • Experiencer and Perceived: – An experiencer is an animate being that perceives something, cognizes about something, or or experiences an emotion. – The perceived is the thing that the experiencer perceives or the thing that caused the emotional response. • The students like linguistics. – (emoter and perceived) • The students saw a linguist. – (perceiver and perceived) • Linguistics frightens the students. – (emoter and perceived) • The students thought about linguistics. – (cognizer and perceived) Examples of Semantic Roles • Patient: A patient is affected by an action. – Sam kicked the ball. – Sue cut the cake. • Beneficiary: A beneficiary benefits from an event – Sue baked a cake for Sam. – Sue baked Sam a cake. • Malefactive: Someone is affected adversely by an event. – My dog died on me. • Instrument: – The boy opened the door with a key. – The key opened the door. • Location: – The clock stands on the shelf. – I put the book on the shelf. Three approaches to semantic roles in meaning representations • Ray Jackendoff (1972, 1990) Linguistic Theory – Lexical Conceptual Structure – The Motion/Location Metaphor – Semantic Roles • Charles Fillmore, FrameNet Project Lexicon – Frame-semantics • Martha Palmer, PropBank Project Corpus Annotation – Predicate-specific role names: – Proto-grammatical relations Ray Jackendoff • Semantic Interpretation in Generative Grammar, MIT Press, 1972 • Semantic Structures, MIT Press, 1990. – Theory of human cognition – Used by many computational linguists Lexical Conceptual Structure • Primitives: – GO, BE, STAY, CAUSE, and several more – TO, FROM, AWAY, TOWARD, VIA, and several more • Types of entities: – Event, State, Thing, Place, Path • Other tiers of representation are added in order to capture nuances of meaning and grammar: – Cause and affectedness – Manner – Actor and undergoer (see discussion of PropBank) Example of Lexical Conceptual Structure Sam threw the ball across the room. [event CAUSE [thing SAM] [event GO [thing BALL] [path TO [place AT [thing other-side-of-room]]]]] Lexical Conceptual Structure and Semantic Role Names Sam threw the ball across the room. [event CAUSE [thing SAM] agent [event GO [thing BALL] theme [path TO [place AT [thing other-side-of-room]]]]] goal The Motion/Location Metaphor • J. S. Gruber, Studies in Lexical Relations, MIT Dissertation, 1965. – Agent: causes, manipulates, affects – Theme: changes location, is located somewhere, or exists – Source: the starting point of the motion – Goal: the ending point of the motion – Path: the path of the motion Examples of Location and Directed Motion • Many problems still exist. • The clock sits on the shelf. • The ball rolled from the door to the window along the wall. • Same walked from his house to town along the river. • Sue rolled across the room. • The car turned into the driveway. Being in a state or changing state • • • • • • The car is red. The ice cream melted. The glass broke. Sam broke the glass. The paper turned from red to green. The fairy godmother turned the pumpkin into a coach. Having or Changing possession • The teacher gave books to the students. • The teacher gave the students books. • The students have books. Exchange of Information • The teacher told a story to the students. • The teacher told the students a story. Extent • The road extends/runs along the river from the school to the mall. • The string reaches the wall. • The string reaches across the room to the wall. Strong points of LCS and the Motion/Location Metaphor • Sam manipulates a key, having an effect on the door, causing it to go from the state of being closed to the state of being open. – Sam opened the door with a key. – The key opened the door. – The door was opened by Sam with a key. – Sam’s opening of the door with a key Strong points of LCS and the Motion/Location Metaphor • A toy goes from Sue to Sam. Some money goes from Sam to Sue. • Differences in the causation tier. – Sam bought a toy from Sue. – Sue sold a toy to Sam. Strong points of LCS and the Motion/Location Metaphor • Supports some inferences: – If X goes from A to B, then X is no longer at A. – If X is created (begins to BE) during event Y, then X doesn’t exist until Y is finished. Strong or weak point? • LCS wasn’t designed for this kind of thing: – Sam took a bus to school. – Sam got on the bus and went to school. – Sam riding on the bus, went to school. – Sam sat on the bus, went to school. – Sam went to school by bus. – Sam went to school by taking a bus. • FrameNet (Fillmore et al.) handles this kind of thing. Problem with Thematic Roles and the Motion/Location Metaphor • It is not clear how to apply the metaphor to many verbs (Fillmore and Kay, Lecture Notes, pages 4-22) – He risked death. – We resisted the enemy. – She resembles her mother. LCS Resources • Bonnie Dorr, University of Maryland • http://www.umiacs.umd.edu/~bonnie/LCS_Da tabase_Documentation.html • LCS Lexicon for English – English word senses are mapped to WordNet – Handcrafted lexical entries for around 4000 verbs – Automatically produced entries may be available for a full-sized lexicon • LCS Dictionaries for other languages may be available – May be handcrafted or produced partially automatically Charles Fillmore, Collin Baker, and others FrameNet Project • http://www.icsi.berkeley.edu/~framenet/ • Frame semantics – Frames are networked using several relations – Based on corpus analysis • Lexical entries for around 7500 English verbs • Other FrameNet projects in – Spanish – Japanese Martha Palmer and others The PropBank Project • http://www.cis.upenn.edu/~ace/ • Annotate the Penn TreeBank with predicate-argument information • Corpus can be used for automatic learning of the surface realization of each argument PropBank and FrameNet: Close ties • PropBank lexical entries are linked to FrameNet entries. – There are more PropBank entries than FrameNet entries • This paper contains some comparisons of PropBank and Framenet – http://www.cis.upenn.edu/~dgildea/gildeaacl02.pdf • See also VerbNet – http://www.cis.upenn.edu/group/verbnet/ Proto-roles and verb-specific roles • http://www.cis.upenn.edu/~dgildea/Verbs/ • Abandon – Arg0:abandoner – Arg1:thing abandoned, left behind – Arg2:attribute of arg1 PropBank: multiple surface realizations of arguments – Sam opened the door with a key. – The key opened the door. – The door was opened by Sam with a key. – Sam’s opening of the door with a key – Arg0:opener – Arg1:thing opening – Arg2:instrument – Arg3:benefactive Sam door key What are the arg-n’s? • The arg-n labels are arbitrary labels. • However, PropBank tries to use them consistently across verbs. – Arg0 tends to be an agent or the argument most likely to be the subject in active voice. – Arg1 tends to be a theme or patient or the thing most likely to be • The direct object of a transitive verb in active voice • The subject of a verb in passive voice • The subject of an intransitive verb PropBank was not designed for this • Sam took a bus to school. • Sam ascended onto the bus and went to school. (Hebrew) • Sam riding on the bus, went to school. (Japanese) • Sam sat on the bus, went to school. (Chinese) • Sam went to school by bus. • Sam went to school by taking a bus. • But it is linked to FrameNet Van Valin: three layers of semantic roles • Verb specific roles: – – – – Writer, reader, kicker, ….. Knower, thinker, realizer, ….. Liker, hater, …… Hearer, seer, feeler, …… • Semantic role classes – – – – Agent Cognizer Emoter Perceiver • Proto Roles – Actor Difference between Van Valin and the movement/location metaphor • Van Valin uses the role patient for things that are called themes in the movement/location metaphor.