Semantic Role Labeling

22.3 Problems with thematic roles

1. What problems arise with thematic roles?
   It is hard to agree on a standard role set or define roles formally; roles fragment into many subtypes; and finite discrete lists don’t support some generalizations. E.g. an AGENT is usually animate, volitional, sentient and causal, but a given NP may lack some of these.
   • Jurafsky & Martin, Speech and Language Processing, 3rd ed. draft, ch. 22, §22.3, p. 502
2. Give an example of role fragmentation for INSTRUMENT.
   Intermediary instruments can be subjects (“The knife cut the banana”), enabling instruments cannot (“Shelly ate the banana with a fork” but *“The fork ate the banana”).
   • Jurafsky & Martin, Speech and Language Processing, 3rd ed. draft, ch. 22, §22.3, p. 502
3. What are PROTO-AGENT and PROTO-PATIENT?
   Generalized semantic roles defined not by necessary and sufficient conditions but by heuristic features: the more agent-like properties an argument has (volitional, causing change, sentient, moving), the likelier it is PROTO-AGENT; the more patient-like (undergoing change, causally affected, stationary), PROTO-PATIENT.
   • Jurafsky & Martin, Speech and Language Processing, 3rd ed. draft, ch. 22, §22.3, p. 502
4. What two alternatives to universal thematic roles do PropBank and FrameNet use?
   PropBank uses proto-roles and verb-specific roles; FrameNet uses roles specific to a frame, a semantic situation shared by a group of words.
   • Jurafsky & Martin, Speech and Language Processing, 3rd ed. draft, ch. 22, §22.3, p. 502