Cs599 Fall2005 Lecture 01

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Cs599 Fall2005 Lecture 01

  1. 1. CS599: Lexical Semantics Course Overview and Introduction Patrick Pantel USC Information Sciences Institute http://www.isi.edu/~pantel pantel@isi.edu Theme Simply put, this course explores the meaning of words Lexical semantics: is the study of how and what the words of a language denote is deeply rooted in Linguistics, but is becoming an increasingly important part of Natural Language Processing (NLP) it covers theories of: the classification and decomposition of word meaning the differences and similarities in lexical semantic structure between different languages the relationship of word meaning to sentence meaning and syntax We will explore different perspectives of lexical semantics, from the point of view of: NLP/AI, Semantics/Philosophy, Linguistics/Lexicography, and Ontologies/KR (Knowledge Representation) Some core issues we will cover: primitives of meaning, the creation of semantically annotated corpora, ontologies, automated methods for acquiring semantic knowledge on a large scale, and a survey of related perspectives © 2005 Patrick Pantel CS599 - Course Overview and Introduction 2 1
  2. 2. Demos http://www.isi.edu/~pantel/demos.htm © 2005 Patrick Pantel CS599 - Course Overview and Introduction 3 Some Definitions… Important terms: Syntax: the study of how words combine to form grammatical sentences Semantics: the study of the meaning of words and how these combine to form the meanings of sentences Lexicography: the study of the design, compilation, use and evaluation of general dictionaries (lexicons) Interlingua: auxiliary language describing the language-independent meaning of a sentence Natural Language Processing vs. Computational Linguistics Applications Information Retrieval (IR): system used for searching a natural language database (e.g. Google, Yahoo!, Microsoft Search) Information Extraction (IE): system used to extract targeted information from structured or unstructured information medium Machine Translation (MT): system that translates spoken/written language from one language to another (e.g. Systran, LanguageWeaver) Question Answering (QA): specific IR system that answers natural language questions with targeted text (instead of returning documents) © 2005 Patrick Pantel CS599 - Course Overview and Introduction 4 2
  3. 3. Lexical Relations Lexical relations are used as tools in this field: synonymy e.g., tome/book, love/adore antonymy (opposition) switching thematic roles associated with the verb (buy – sell) stative verbs (live – die) sibling verbs which share a parent (walk – run) restitutive opposition: antonymy + happens-before (damage - repair) hyponymy/hypernymy (subclass/superclass) e.g. stool is-a chair, apple is-a fruit, face is-a external-body-part meronymy/holonymy (part-of/has-part) e.g. wheel part-of car, chair part-of committee, face part-of head cause, strength, temporal precedence, entailment… © 2005 Patrick Pantel CS599 - Course Overview and Introduction 5 Logistics Course: CS599 – Lexical Semantics (3 units) Course website: http://www.isi.edu/~pantel/Content/Teaching/2005/cs599.htm Class schedule: Tuesday/Thursday: 2:00 pm - 3:20 pm (GFS107) Instructors: Prof. Eduard Hovy (CS) Prof. Jerry Hobbs (CS) Prof. Robert Belvin (Ling) Prof. Patrick Pantel (CS) Office hours: TBA Grading: 4 assignments (25% each) Readings: Instructors will recommend foundation and cutting edge papers as weekly readings. © 2005 Patrick Pantel CS599 - Course Overview and Introduction 6 3
  4. 4. What I need from you… Please email the following information to pantel@isi.edu before the next class Full name + student number Email address Home department Are you taking the class for credit or are you auditing it? Are you familiar with the programming language Perl? What other programming languages do you use? Do you have any comments or concerns? © 2005 Patrick Pantel CS599 - Course Overview and Introduction 7 Course Outline Module 1 - Computational Lexical Semantics (Prof. Pantel) Computational formulation of lexical semantics Statistics and information theory Automated methods for harvesting semantics (corpus- and web-based) Applications (building a thesaurus, extracting paraphrases, discovering word classes, inducing word senses, automatically linking learned knowledge into formal ontologies) August 25, 30; September 1, 6, 8, 27 (with Hovy) Module 2 - Deep Lexical Semantics (Prof. Hobbs) Introduction to deep lexical semantics Interpretation as abduction Cognition and the cognitive lexicon Time and the word quot;Now“ Causality and modality Similarity and the preposition quot;Like“ September 13, 15, 20; October 18, 20, 25, 27 © 2005 Patrick Pantel CS599 - Course Overview and Introduction 8 4
  5. 5. Course Outline Module 3 - Ontologies (Prof. Hovy) Semantic primitives Introduction to ontologies Ontologies for shallow semantics Upper and middle models Verb sense frames The Omega ontology September 22, 27 (with Pantel), 29; November 8, 10, 15, 17, 22 Module 4 - Linguistic Issues (Prof. Belvin) Semantic cases, semantic fields Thematic relations hypothesis Lexical semantic decomposition Verb classes and alternations Formalisms and notation Mapping October 4, 6, 11, 13; November 1, 3, 29 © 2005 Patrick Pantel CS599 - Course Overview and Introduction 9 Course Outline Module 5 – Annotation of Shallow Semantics (Prof. Hovy) Sense annotation as in PropBank The giant leap from senses to concepts Annotation and verification of sense and concept creation November 17, 22 © 2005 Patrick Pantel CS599 - Course Overview and Introduction 10 5
  6. 6. Grading There will be four assignments, each worth 25% Assignment 1: Corpus- and web-based knowledge harvesting (programming) Assignment 2: Deep lexical semantics Assignment 3: Syntax to semantics mapping Assignment 4: Annotation of shallow semantics © 2005 Patrick Pantel CS599 - Course Overview and Introduction 11 A Few Prominent Figures CS: Linguistics: Christiane Fellbaum Bernard Comrie William Croft Graeme Hirst Charles Fillmore Jerry Hobbs Ken Hale Mitch Marcus Ray Jackendoff Dan Moldovan George Lakoff Sergei Nirenburg Ronald Langacker Beth Levin Martha Palmer James McCawley James Pustejovsky Leonard Talmy Roger Shank Anna Wierzbicka … … © 2005 Patrick Pantel CS599 - Course Overview and Introduction 12 6
  7. 7. Module 1 - Computational Lexical Semantics Prof. Patrick Pantel (CS) August 25, 30; September 1, 6, 8, 27 Topics: Computational formulation of lexical semantics Distributional Hypothesis Links the semantics of words to the syntactical uses Words that occur in the same contexts tend to have similar meanings A bottle of tezgüno is on the table. Everyone likes tezgüno. Tezgüno makes you drunk. We make tezgüno out of corn. What is tezgüno? © 2005 Patrick Pantel CS599 - Course Overview and Introduction 13 Module 1 - Computational Lexical Semantics Topics (continued…): Statistics and information theory Mutual information, log-likelihood, similarity metrics Text- and web-mining algorithms for harvesting word semantics, and semantic relations between words Applications building a distributional thesaurus extracting paraphrases discovering word classes inducing word senses automatically linking harvested knowledge into formal ontologies © 2005 Patrick Pantel CS599 - Course Overview and Introduction 14 7
  8. 8. Module 2 - Deep Lexical Semantics Prof. Jerry Hobbs (CS) September 13, 15, 20; October 18, 20, 25, 27 Topics: Introduction to deep lexical semantics Interpretation as abduction Cognition and the cognitive lexicon Time and the word quot;Now“ Causality and modality Similarity and the preposition quot;Like“ © 2005 Patrick Pantel CS599 - Course Overview and Introduction 15 Module 3 - Ontologies Prof. Eduard Hovy (CS) September 22, 27, 29; November 8, 10, 15, 17, 22 Topics: Shallow semantics When and why do we need shallow semantics? MT toward interlinguas, better IR/IE/summarization Ontology: conceptualization of knowledge domain Controlled vocabulary of all concepts + a set of relations that link concepts + language to make queries / assertions / inferences Upper model, middle model, domain models Dealing computationally with shallow semantics Ontology vs. lexicon Looking under the hood of ontologies The WordNet termbank (ontology?) The Omega ontology © 2005 Patrick Pantel CS599 - Course Overview and Introduction 16 8
  9. 9. Module 4 - Linguistic Issues Prof. Robert S. Belvin (Ling) October 4, 6, 11, 13; November 1, 3, 29 Topics: Linguistic study of lexical semantics with focus on benefits for automated systems Lexical semantics vs. lexicography vs. formal semantics Different views of the language faculty and how that can impact how we do semantic representation and mapping Gruber's thematic relations hypothesis Lexical semantic decomposition some semantic primitives, cross-categorical semantic features, languages which have transparent decomposition/morphologically complex forms, lexicalization patterns (in English and cross- linguistically) © 2005 Patrick Pantel CS599 - Course Overview and Introduction 17 Module 4 - Linguistic Issues Topics (continued…) Verb Classes and Alternations valence-changing operations (in English and cross-linguistically) the quot;unaccusativequot; hypothesis Some Formalisms and Notation Lexical Conceptual Structure Parsons Event Semantics Image-schemas Mapping how do you get semantic representation out of syntactic structure? subcategorization and selection thematic role hierarchy and universal theta alignment hypothesis semantic contribution of syntactic structure © 2005 Patrick Pantel CS599 - Course Overview and Introduction 18 9
  10. 10. Module 5 - Annotation of Shallow Semantics Prof. Eduard Hovy (CS) November 17, 22 Topics: Manually acquiring shallow semantic knowledge is a difficult task Determine what you want Derive a representational formalism that captures it Get people to do it!! (or get machines!!!) Lexical term creation, definition and extraction Manual effort based on inter-annotator agreement How do we ensure consistency and quality Senses vs. concepts © 2005 Patrick Pantel CS599 - Course Overview and Introduction 19 10

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