Layering Semantics (Putting meaning into trees) Treebank Workshop Martha Palmer April 26, 2007

Treebank Workshop/NAACL07 Outline Semantic role labeling, verbs and nouns Treebank/PropBank discrepancies Treebank/NomBank discrepancies Dependencies vs. Phrase Structure

Treebank Workshop/NAACL07 A TreeBanked phrase a GM-Jaguar pact NP S VP would VP give the US car maker NP an eventual 30% stake NP the British company NP PP-LOC in A GM-Jaguar pact would give the U.S. car maker an eventual 30% stake in the British company. Marcus, et al, 1993

Treebank Workshop/NAACL07 The same phrase,PropBanked* a GM-Jaguar pact would give the US car maker an eventual 30% stake in the British company Arg0 Arg2 Arg1 give(GM-J pact, US car maker, 30% stake) A GM-Jaguar pact would give the U.S. car maker an eventual 30% stake in the British company.

Treebank Workshop/NAACL07 Frames File example: give Roles: Arg0: giver Arg1: thing given Arg2: entity given to Example: double object The executives gave the chefs a standing ovation. Arg0: The executives REL: gave Arg2: the chefs Arg1: a standing ovation

Treebank Workshop/NAACL07 NomBank Frame File example: gift (nominalizations, noun predicates, partitives, etc. Roles: Arg0: giver Arg1: thing given Arg2: entity given to Example: nominalization Nancy’s gift from her cousin was a complete surprise. Arg0: her cousin REL: gave Arg2: Nancy Arg1: gift

Treebank Workshop/NAACL07 Status of TB/PB merge Extracted and classified mismatch examples Reconciled different policy decisions  An example of TB changes: Modified list of verbs which take small clauses and sentential complements (e.g. keep their markets active)  An example of PB changes: A different approach to annotation of empty categories: John seems [*T* to know the answer]-Arg1 Some mismatches require manual adjudication  (e.g. PP-attachment ambiguity): The region lacks necessary mechanisms for handling the aid and accounting items. Unresolved issues: gapping

Treebank Workshop/NAACL07 Treebank-PropBank Reconciliation Problem: One PropBank arg can involve many parse nodes Solution: Single argument – single parse node analysis Problem: Different semantic analyses Solution: Reconcile semantic assumptions

Treebank Workshop/NAACL07 NomBank Issues Treebank has no structure for noun phrases Many nominal event arguments do not correspond to tree nodes

Treebank Workshop/NAACL07 Dependency Trees vs Phrase Structure CATEGORYDTPST Finding constituent boundaries√ Noun phrase structure√ Empty categories√ Coordination – what is the head?√ Phrasal verbs√ Discontinuous constituents√

Treebank Workshop/NAACL07 Dependency Trees vs Phrase Structure Really depends on choices with respect to guidelines and the annotation tool display  Penn Treebank chose not to bracket NP’s  Dependency trees can be displayed visually to clarify constituent structure  Empty categories can be a help or a hindrance depending on the annotator’s task  Coordination heads are defined in the guidelines  Penn Treebank could define phrasal verbs