VerbNet

1. VerbNet A Class-Based Verb Lexicon Magdalena Leshtanska

2. Overview VerbNet – basic idea The Levin Verb Classification - overview, drawbacks, refinement VerbNet Classes – LTAG Examples References

3. VerbNet Largest online verb lexicon for English Hierarchical structure of intersected Levin verb classes LTAG formalism captures syntax for each verb class and assigns semantic predicates Links to other lexical resources e.g. WordNet

4. The Levin Verb Classification Approaches towards forming verb classes Predict syntax, using semantic information I can buy a house vs *I can think a house Predict semantics, using syntactic information to hit someone vs to hit on someone Levin (1993) Assumes the sets of syntactic frames a verb can appear in reflect underlying semantic components that constrain allowable arguments Classes are based on the (in)ability of a verb to occur in pairs of meaning preserving syntactic frames (diathesis alternations)

5. Example – break and cut Transitive construction John broke the window. John cut the bread. Middle construction Glass breaks easily. This loaf cuts easily. Simple intransitive construction The window broke. *The bread cut. Conative construction John cut at the loaf, but his knife was too dull to make a dent in it. *John broke at the window. cut describes actions directed at achieving the goal of separating an object into pieces. break can‘t occur in the conative, cause it only specifies a resulting change of state – an object is separated into pieces If state is unchanged, no breaking actions are recognized.

6. The Levin Verb Classification - Drawbacks Inconsistencies – verbs can exist in multiple lists, sometimes with conflicting structure Levin explicitly states the syntax for each class, but falls short of assigning semantic components to each. And syntax alone is not enough: John left the ball on the field (gave away) John left the field (went out) But: John left a fortune (gave away)

7. Levin Classes - Refinement (Dang 1998) Intersective Levin classes If more than 3 members from intersected classes overlap, they‘re moved to a subcalss of their own Result: a fine-grained version, suitable for applications

8. VerbNet Classes Hierarchically organized Class members share features a verb or subclass inherits features from the parent and may add more information Capture both syntax and semantics Thematic roles - Agent, Theme, Location,.. Syntactic frames. Each frame has selectional restrictions for the arguments in it – e.g. the agent of „run“ should be animate semantic predicates with a time function

9. VerbNet Classes - LTAG Classes modelled by LTAG (Lexicalized Tree-Adjoining Grammar) LTAG allows to generate syntactic variants, e.g. passive from declarative incorporate semantics into the model

10. LTAG - Run

11. LTAG Syntactic Frames Come as an ordered sequence of thematic roles John hit the ball - Agent V Patient John hit at the window - Agent V at Patient John hit the sticks together – Agent V Patient[+plural] together Adorned with a conjunction of semantic predicates. Semantic predicates can be General (e.g. cause, motion) Specific (e.g.,suffocate) Variable (Prep) Each predicate includes a time function showing at what stage in the event it holds: start, during, end, result

12. LTAG - Hit

14. Members, Roles & Class Hierarchy

15. Syntactic Frames – Hit 18.1

16. …Semantic representation

17. References Hoa Trang Dang, Karin Kipper, Martha Palmer and J. Rosenzweig. 1998 “Investigating Regular Sense Extensions Based on Intersective Levin Classes”. In Proceedings of Coling-ACL98. Montreal, CA. Hoa Trang Dang, Karin Kipper, and Martha Palmer 2000. Integrating compositional semantics into a verb lexicon. In Proceedings of the Eighteenth International Conference on Computational Linguistics COLING- 000), Saarbrücken, Germany, July- August. Karin Kipper, Hoa Trang Dang, and Martha Palmer. 2000a. Class-based construction of a verb lexicon. In Proceedings of the Seventh National Conference on Artificial Intelligence (AAAI-2000), Austin, TX, July-August. Beth Levin. 1993. English Verb Classes and Alternation, A Preliminary Investigation. The University of Chicago Press.

18. Thank you!Questions?

19. Additional information - Background - LTAG Consists of initial and auxiliary elementary trees Initial trees capture non-recursive structures of a language, e.g. a verb and its complements Auxiliary trees capture recursive structures, e.g. prepositional modifiers <example graphs> Two operations to combine the trees Substitution – replaces a tree leaf with a new tree Adjunction – replaces an internal node with an auxiliary tree Every tree is associated with a lexical item – anchor that specifies constraints, implemented as features Each lexical entry corresponds to a tree and trees are adjoined together. This composition is recorded in a derivation tree. <example>