Some Semantic Issues

Logical Form vs. Final Representation

• Logical form: representation of context-independent sentence meaning vs. contextually interpretation form in knowledge-representation language
• I will grade the exam.
  LF (informally): The speaker grade (FUTURE) an exam that is uniquely determined in the context.
  KR (informally): MG will grade EXAM167 sometime following 12:45 am on Oct. 31, 1997.

From First-Order Predicate Calculus

• Object constants (EXAM167) and relation constants (GRADE-EXAM, EXAM, DIFFICULT) to represent word senses.
• Logical connectives: AND, OR, NOT, IF (the best HTML can do with the symbols); but these don't correspond neatly to English conjunctions/adverbs
  • Tom likes Sue and Mary.
    Like(Tom, Sue) AND Like(Tom, Mary)
  • Tom went home and had a drink.
    and has a sequential interpretation.
  • Tom likes Sue or Mary.
    Like(Tom, Sue) OR Like(Tom, Mary)
  • Tom doesn't like Sue or Mary.
    (NOT (Like(Tom, Sue))) AND (NOT (Like(Tom, Mary)))
  • If I feel sick, I go to the doctor.
    Unlike logical IF, if may carry an implication of only if: I only go to the doctor if I feel sick
  • If you're thirsty, there's some beer in the refrigerator.
    With if, some implicational steps may be missing: If you're thirsty, you may want to drink something. If you want to drink something, you will need to know wehre it is. If you want to know where something is, I can inform you where it is by asserting its location.
• Quantifiers: FOR-ALL, EXISTS
  • I read a book.
  • Everybody likes Bob.

On Top of First-Order Predicate Calculus

• Generalized quantifiers to handle most, the, etc.
  Most students are clueless. MOST x: Student(x), Clueless(x)
• Predicate operator to handle PLURAL
  The students are clueless. THE x: (PLURAL STUDENT)(x), Clueless(x)
• Modal operators to handle BELIEVE, WANT, tense, etc.
  Equivalent terms cannot be substituted with belief, etc. contexts: Mary believes that John is an idiot. and Mary believes that Susan's husband is an idiot. do not have the same truth conditions even if John is Susan's husband because Mary may not know this.

Some Kinds of Ambiguity

• Scope
  • At every hotel you can find a receptionist.
  • At every hotel you can find a weird guy wearing a gorilla costume.
  • At every hotel you can find the receptionist.
  • Phyllis didn't drop the class because it met early.
• Indefinite reference
  • I'm looking for a novel by Hemingway. (any one or a specific one)
• Definite reference
  • Bring me the biggest tomato in the garden. (role interpretation)
  • I always like the people who live next door. The President changes often. (ambiguous between role and value interpretations)

Thematic (Semantic) Roles (Cases)

• The same syntactic case (for example, subject) can signal very different semantic roles for different verbs which are related in meaning.
  Phyllis {likes, detests, trusts, envies, respects} Harold. Phyllis {pleases, sickens, inspires, moves, bores} Harold.
  Martha {saw, heard, smelled, tasted, felt} the squid. Martha {looked at, listened to, smelled, tasted, felt} the squid.
• In different languages, the same semantic role may correspond to different syntactic roles (for example, direct object in English, subject in German).
  I like you. Du gefällst mir. (German)
• The same verb may be associated with different case frames, that is, different patterns of associations between syntactic and semantic roles.
  The vase shattered. The ball shattered the vase. Terry shattered the vase with the ball.
  Hal smeared peanut butter on the wall. Hal smeared the wall with peanut butter.
• Some ambiguity concerns semantic case.
  Jimmy pushed the truck under the table.
• What semantic cases?
  • Specific ones: SEER, SEEEE
  • General ones: AGENT, PATIENT, INSTRUMENT, RECIPIENT, EXPERIENCER, THEME, DESTINATION, SOURCE, LOCATIVE, TIME, BENEFACTIVE, ADVERSATIVE, CO-AGENT, CO-PATIENT
  • A case frame for a specific verb

    [RELN see
     SEER <...SUBJECT | CONTENT | INDEX>
     SEEEE <... DIROBJ | CONTENT | INDEX>]
    

  • A case frame which can be shared by several verbs

    [RELN perceive
     EXPER <...SUBJECT | CONTENT | INDEX>
     THEME <...DIROBJ | CONTENT | INDEX>]
    

• Verbs with different case frames

  "break1":
  [RELN break
   AGENT <...SUBJECT | CONTENT | INDEX>
   PATIENT <...DIROBJ | CONTENT | INDEX>
   (INSTR <...PP | HEAD | PHON "with">)]
  
  "break2":
  [RELN break
   INSTR <...SUBJECT | CONTENT | INDEX>
   PATIENT <...DIROBJ | CONTENT | INDEX>]
  
  "break3"
  [RELN break
   PATIENT <...SUBJECT | CONTENT | INDEX>]