NLU: Frames

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
• Theyre 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).
• Theyre 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 Jacks 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
Frame Based Formalism
The kind man gave a bread to the beggar for his
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
  based on 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)