Interpreting Dictionary Definitions Dan Tecuci May 2002

Problem Description Interpretation = translating into one's own language Given: Dictionary definitions of actions KB = set of primives/components Argument structure Text generation Axioms Pre/post/during conditions User input Produce Representations of actions

Example Dictionary: carry = to move while supporting Challenges: Identify what primitive components are referred Move, Support Deal with missing arguments An agent moves an object while supporting it Resolve references between them Agent1 moves object2 while Agent1 supports object2 Identify deep semantic relations among them There are two subevents of Carry, one in which Agent1 move s object2 and one in which Agent1 support s object2 so that object2 cannot fall, and they happen in parallel

What Is the Goal? Acquire different kinds of knowledge: Taxonomic Semantics of actions Argument structure In order to: Accelerate knowledge acquisition Execute actions Talk about them Understand when someone talks about them

Knowledge of Argument Structure What arguments does the verb have and where they surface (position) Multiple ways in which an argument can surface. – E.G. V+o[+a] -> carry something [somewhere]. The reverse of text-gen

Motivation Why this task Fast, automatic knowledge acquisition Language understanding and generation Available source of knowledge Why dictionaries Structured source of knowledge Taxonomic Argument structure Could be extended to full natural language Has been done before (manually)

Related Work - R. Amsler "The structure of MW dictionary" 80 Analyses definitions based on “kernels” (superclasses) Main goal - build a taxonomy of motion verbs Other Procedure to analyse the argument structure of motion verbs (look at usage in other definitions and use componential analysis) Manual WSD, manual kernel identification, automatic taxonomy building

Related Work - C. Barrière “From a children dictionary to a LKB” Automatic translation of dictionary definitions into a knowledge representation formalism Specifics Uses an intermediary representation Only 1 sense of a word is analysed Children dictionary has usage examples

Related Work - C. Hastings Tries to acquire word (mainly verb) meaning from context (sentence) Uses LINK parser, semantic knowledge, terrorism domain KB has detailed info, fine-grained constraints Uses rules based on sentence structure to detect case-role assignment Syntactic/semantic knowledge is expressed in the same formalism (LINK) Algorithm: Identify slot fillers Based on this, identify matching components

Related Work - FrameNet Mainly the same goal, but bottom-up Not based on composing a set of primitives Manually annotate sentences, automatically capture the organization of the annotation results Frame – frame elements How FEs are realized in language Executable?

Dictionary Definitions Advantages +Good source of taxonomic knowledge +Follow a “genus-differentia” pattern +Some dictionaries tend to define everything in terms of a basic vocabulary Disadvantages -Definitions are elliptical -Incomplete sentences (not easier to parse then NL) -Leave blank argument positions that are nearly always filled in usage -One definition does not provide enough info

What We Need What kind of knowledge do we need for such a task? Knowledge about primitive components Semantic - meaning Syntactic - argument structure How to determine when a concept is referenced? Knowledge about how to compose them and how this is reflected in language

Complex Actions What are complex actions? How to discover them? Dictionaries

Example - Steps Carry = to move while supporting Steps: 1.Identify referenced concepts/components 2.Identify their arguments 3.How are the components assembled 4.Resolve references 5.Get knowledge about argument structure

Identifying components TaskMethod i) Identify verbs - they constrain and interrelate the entities mentioned in sentences. POS tagging ii) What sense(s) are used? Word-sense disambiguation iii) What components do they match? SME Dictionary Example: move #1, support#4 Move, Support

Arguments of Move, Support ? From definition Problem: definitions omit args that are usu. present KB Minimal number of required args Arguments of Carry Suggested by: syntax dictionary: transitive/intransitive definitional patterns - Carry ISA Move How are they related ? Identifying the arguments

Assembling the components Meaning of the whole = function of parts and the way they are composed Discover deep semantic relations among components referenced Prepositions – clues Example: “while” – co-temporality or detraction “by”- by-means-of, agent, time, location… Rules based on features of components How to test if a component is correct/coherent? (test-cases?)

Resolving co-references What object are co-referential? the agent of Move = the agent of Support the object of Move = the agent of Support How to do it? Heuristic – assume everything maps unchanged unless there is reason to believe otherwise Matching Machine learning

KB Move 16 senses in WN represented in CompLib – tr. & intr. What about argument structure? Multiple argument structure can correspond to a sense Argument structures Subj + Move => agent ~ Subj Subj + Move + DObj => agent ~ Subj, object ~ object …

KB (cont.) – Arg Struct for Move Full arg structure for Move “agent moves object over distance using instrument along path from source to destination ” How to Acquire such knowledge? Express it? All possible trees Constraints (Subj always before Pred.)

Observations Verb definitions differ in level of generality More general - elliptical definitions “Carry = move while supporting” Inherit more from primitive components More specific - more complete definitions “Bioremediation = treating waste or pollutants by the use of microorganisms (as bacteria) that can break down the undesirable substances” Highly specialized versions of supers

What's next Focus on a subproblem (e.g. WSD) Get data (FrameNet?) Design an experiment Compare to existing methods

Research questions What dictionary to use? (WN?) How to represent arg struct knowledge? How would the special nature of the knowledge we have might help in this task? actions can be executed their results can be tested Does compositionality help?