6.863J Natural Language ProcessingLecture 16: the boundaries of syntax & semantics – towards constraint-based systemsRobert C. [email protected]/9.611J Lecture 16 Sp03The Menu Bar• Administrivia:• Lab 4 due April 9? (what about Friday) • Start w/ final projects, unless there are objections• Agenda: • Shallow instead of ‘deep’ semantics: MUC• Stochastic language use? Some examples• How to accommodate: towards constraint-based grammar6.863J/9.611J Lecture 16 Sp03How to integrate all this stuff?• We saw that we might want to partition syntactic knowledge from semantic…• But we have to go farther – because both of these might be probabilistic in nature• How to integrate?6.863J/9.611J Lecture 16 Sp03Integration• One way: semantic grammar (see below)• The way we’ll explore though:• Define linguistic structure• Place pr distributions on that structure6.863J/9.611J Lecture 16 Sp03Example• Syntactic rule = NP à Det N• Semantic extension = NP : Apply(lambda (x) (DEF/SING x), N)• Lexicon:• Art:the: DEF/SING• N:guy: Person• Parse of the NP the guy:• NP à Det N ⇒ OK, NP contains article & noun• Apply (lambda (x) (DEF/SING x), N) ⇒ OK, NP contains DEF/SING article• Apply (lambda (x) (DEF/SING x), Person) ⇒ the N in the NP is Person• (DEF/SING Person) ⇒ result of applying lambda calculus ⇒textual replacement of variable x with argument Person6.863J/9.611J Lecture 16 Sp03Another Example• S à NP VP Apply(VP, NP)• VP à V NP Apply(Apply(V, NP), NP)• Lexicon look-up Apply(Apply(lambda(o) lambda(x) (kiss past [agent x] [theme o]), NP), NP)• NP à ART N Apply(Apply(lambda(o) lambda(x) (kiss past [agent x] [theme o]),Apply(lambda (x) DEF/SING x), N)), NP)• Lexicon look-up Apply(Apply(lambda(o) lambda(x) (kiss past [agent x] [theme o]),Apply(lambda (x) (DEF/SING x), DOG)), NP)• Apply -operator Apply(Apply(lambda(o) lambda(x) (kiss past [agent x] [theme o]), (DEF/SING DOG), NP)• Apply -operator Apply(lambda(x) (kiss past [agent x] [theme DEF/SING DOG]), NP)NP à ART N Apply(lambda(x) (kiss past [agent x] [theme DEF/SING DOG]), Apply(lambda(x) (DEF/SING * x), N))• Lexicon look-up Apply(lambda(x) (kiss past [agent x] [theme DEF/SING DOG]), Apply(lambda(x) (DEF/SING * x), Person))• Apply -operator Apply(lambda(x) (kiss past [agent x] [theme DEF/SING DOG]), (DEF/SING Person))• Apply -operator (kiss past [agent DEF/SING Person] [theme DEF/SING DOG])Lexicon:V:kissed = lambda(o) lambda(x) (kiss past [agent x] [theme o])N:guy = personN:dog = DOGDet:the = DEF/SINGTop-down parse sentence:The guy kissed the dogSyntax:S à NP VPVP à V NPNP à Det NSemantics:S : Apply(VP, NP)VP : Apply(V, NP)NP : Apply(lambda (x) (DEF/SING x), N)6.863J/9.611J Lecture 16 Sp03Semantic Grammar: Definition• Syntactic and semantic processing is collapsed in a single framework• Like a regular grammar but terminal symbols are replaced by semantic categories• Example:• [VP read [NP a book]] or [write [a book]]VP à V NP⇓READ-VP à READ-VERB READ-STUFFWRITE-VP à WRITE-VERB WRITE-STUFF6.863J/9.611J Lecture 16 Sp03Example of a Grammar• RES-VP → RESERVING RES-MOD• RES-VP → RESERVING• DEP-VP → DEPARTING DEP-MODS• RESERVING → RESERVE-VERB FLIGHT• RES-MOD → for PERSON• DEPARTING → DEPART-VERB• DEPARTING → DEPART-VERB SOURCE-LOCATION• DEP-MODS→ DEP-MOD DEP-MODS• DEP-MODS→ DEP-MOD• DEP-MOD → to DEST-LOCATION• DEP-MOD → from SOURCE-LOCATION6.863J/9.611J Lecture 16 Sp03Exercise• Grammar:RES-VP à RESERVINGRES-VP à RESERVING RES-MODRESERVING à RESERVE-VERB FLIGHT-NPRES-MOD à for PERSONFLIGHT-NP à ART FLIGHT-NOUNFLIGHT-NP à ART FLIGHT-NOUN FLIGHT-MODSFLIGHT-MODS à FLIGHT-MOD FLIGHT-MODSFLIGHT-MODS à FLIGHT-MODFLIGHT-MOD à from SOURCE-LOCATIONFLIGHT-MOD à to DEST-LOCATION• Lexicon:FLIGHT-NOUN:flightART:aPERSON:meLOCATION:BostonLOCATION:ChicagoRESERVE-VERB: bookParse this sentence (bottom-up):Book a flight from Boston to Chicago for me6.863J/9.611J Lecture 16 Sp03Solution (1)• FLIGHT-MOD à from SOURCE-LOCATIONBook a flight [FLIGHT-MOD from SOURCE-LOCATION Boston] to Chicago for me• FLIGHT-MOD à to DEST-LOCATIONBook a flight [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MOD to DEST-LOCATION Chicago] for me• FLIGHT-MODS à FLIGHT-MODBook a flight [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MODS [FLIGHT-MOD to DEST-LOCATION Chicago]] for me• FLIGHT-MODS à FLIGHT-MOD FLIGHT-MODSBook a flight [FLIGHT-MODS [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MODS [FLIGHT-MOD to DEST-LOCATION Chicago]]] for me6.863J/9.611J Lecture 16 Sp03Solution (2)• FLIGHT-NP à ART FLIGHT-NOUN FLIGHT-MODSBook [FLIGHT-NP ART a FLIGHT-NOUN flight [FLIGHT-MODS [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MODS [FLIGHT-MOD to DEST-LOCATION Chicago]]]] for me• RESERVING à RESERVE-VERB FLIGHT-NP[RESERVING RESERVE-VERB Book [FLIGHT-NP ART a FLIGHT-NOUN flight [FLIGHT-MODS [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MODS [FLIGHT-MOD to DEST-LOCATION Chicago]]]]] for me• RES-MOD à for PERSON[RESERVING RESERVE-VERB Book [FLIGHT-NP ART a FLIGHT-NOUN flight [FLIGHT-MODS [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MODS [FLIGHT-MOD to DEST-LOCATION Chicago]]]]] [RES-MOD for PERSON me]• RES-VP à RESERVING RES-MOD[RES-VP [RESERVING RESERVE-VERB Book [FLIGHT-NP ART a FLIGHT-NOUN flight [FLIGHT-MODS [FLIGHT-MOD from SOURCE-LOCATION Boston] [FLIGHT-MODS [FLIGHT-MOD to DEST-LOCATION Chicago]]]]] [RES-MOD for PERSON me]]6.863J/9.611J Lecture 16 Sp03Useful?• Semantic grammars are useful in a limited domain• Dialogue system to book flights through the telephone• For general use à too many rules!6.863J/9.611J Lecture 16 Sp03Application Continuum• Machine Translation• Unrestricted language comprehension• Summarization• Information extraction• Find specific information: location, names of terrorists, …• Text classification• What is the text about (topic detection)?• Information retrieval6.863J/9.611J Lecture 16 Sp03Information Extraction• Analyzing unrestricted, unstructured text• Extracting specific structured information • Enabling technology• Converting text to a database (data mining)• Summarization6.863J/9.611J Lecture 16 Sp03Example from the terrorism domainInput:San Salvador, 19 Apr 89. Salvadoran President-elect Alfredo Cristiani condemned the terrorist killing of Attorney general Roberto Garcia Alvarado and accused the Farabundo Marti
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