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NLU: Frames

NLU: Frames. Frame KR is a good way to represent common sense can define stereotypical aspects of some domain we are interested in analyzing sentences about that domain can be parsed, and their meaning extracted in terms of what the frames expect

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NLU: Frames

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  1. NLU: Frames • Frame KR is a good way to represent common sense • can define stereotypical aspects of some domain we are interested in analyzing • sentences about that domain can be parsed, and their meaning extracted in terms of what the frames expect • actions: activity of a sentence, specified by verb phrase • thematic role (of a noun phrase): how the object participates in the action of a sentence

  2. sentence analysis: • what thematic roles are to be filled by a sentence • determining thematic roles of noun phrases • many theories define different thematic roles; common objective is to determine adequate constraints (logical limitations) between action and thematic roles

  3. What are semantic roles and what is their history? • A lot of forms of traditional grammar (Sanskrit, Japanese, …) analyze in terms of a rich array of semantically potent case ending or particles • They’re kind of like semantic roles • The idea resurfaces in modern generative grammar in work of Charles (“Chuck”) Fillmore, who calls them Case Roles (Fillmore, 1968, The Case for Case). • They’re quickly renamed to other words, but various: • Semantic roles • Thematic roles • Theta roles • A predicate and its semantic roles are often taken together as an argument structure

  4. Okay, but what are they? • An event is expressed by a predicate and various other dependents • The claim of a theory of semantic roles is that these other dependents can be usefully classified into a small set of semantically contentful classes • And that these classes are useful for explaining lots of things

  5. Common semantic roles • Agent: initiator or doer in the event • Patient: affected entity in the event; undergoes the action • Sue killed the rat. • Theme: object in the event undergoing a change of state or location, or of which location is predicated • The ice melted • Experiencer: feels or perceive the event • Bill likes pizza. • Stimulus: the thing that is felt or perceived

  6. Common semantic roles • Goal: • Bill ran to Copley Square. • Recipient (may or may not be distinguished from Goal): • Bill gave the book to Mary. • Benefactive (may be grouped with Recipient): • Bill cooked dinner for Mary. • Source: • Bill took a pencil from the pile. • Instrument: • Bill ate the burrito with a plastic spork. • Location: • Bill sits under the tree on Wednesdays

  7. Common semantic roles Try for yourself! • The submarine sank a troop ship. • Doris hid the money in the flowerpot. • Emma noticed the stain. • We crossed the street. • The boys climbed the wall. • The chef cooked a great meal. • The computer pinpointed the error. • A mad bull damaged the fence on Jack’s farm. • The company wrote me a letter. • Jack opened the lock with a paper clip.

  8. Thematic roles • Agent: the passive or active entity that causes an action • Donald kicked the ball. • Co-agent: partner with agent • Donald kicked the ball with his friend Mickey. • Thematic object: the object undergoing change, to which the action is being applied • Donald kicked the ball. • Instrument: tool used by agent • Donald kicked the ball with his foot. • Location: where action occurs • Donald kicked the ball on the field. • and others

  9. To Whom? (Co-Agent) Who’s Giving? (Agent) Giving What? (Theme) GIVE For Whom (Beneficiary) Where? (@loc) When? (Time) Frame Based Formalism The kind mangavea breadtothe beggarforhis hungry child.

  10. Frame based formalism (contd.) • Partial instantiation of a frame is possible. • Different verbs can have different frames. • The domain of a role is dependent on the verb. • Frame is instantiated based on the input provided by the user. • Role can be a single concept or a composition basedon qualifier-qualified structure.

  11. Filled thematic roles • Robbie made coffee for Suzie with a percolator.

  12. Thematic roles and parsing • In easy sentences, thematic roles are ascertainable by from grammar: • verb constrains thematic roles, and placement of noun phrases • propositions limit noun phrase role possibilities • eg. by : agent or conveyance or location • with : co-agent or instrument • to : destination • nouns may limit roles • main noun phrase determines roles of others • still lots of ambiguities: need a large lexicon! • Time flies like an arrow. • Fruit flies like a banana.

  13. Constraints • Constraint: an enforced problem-specific limitation • the main task of NLU is to exploit contraints of grammar, phrases, thematic roles on one another to determine an overall (hopefully unambiguous) meaning • without constraints, there are too many possible meanings and thematic roles • humans can quickly ascertain the constraints of a sentence • but you can write ambiguous ones too: • I gave the celery to the rabbit and then ate it. • We can predefine word meaning, and use to establish permissible constraints • but there can be a lot! (how many meanings of “take”)

  14. Constraints and frames • frame representations • slots: thematic roles • action frames: specify sentence action • state-change frames: resulting change of state of thematic roles that occur through action • result link: indicates change of state from an action, & points to state-change frame • meanings of sentences represented by state changes • primitive action systems: a frame system in which: • a primitive action slot is filled from a small set of actions • state change slots indicate result of primitive actions • can be used to determine what happened in sentence (explicitly and implicitly)

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