What is discourse? An Introduction M.Sc. Seminar: Discourse Coherence Theories and Modeling Annemarie Friedrich & Alexis Palmer Department of Computational Linguistics, Saarland University 22 April 2013 Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 1 / 20
Outline 1 Discourse 2 Relevant linguistic concepts Computational approaches 3 Coherence 4
Discourse Senses of “discourse” • Styles of communication • Argument, rhetoric • Ways of talking about things • Multi-party communication • Conversation • Dialogue • Everything beyond the level of the sentence • Linguistic notion of discourse • i.e. TEXT Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 3 / 20
Discourse The importance of text Example Europe’s Herschel space telescope has imaged one of the most popular subjects in the sky - the Horsehead Nebula - and its environs. The distinctively shaped molecular gas cloud is sited some 1,300 light-years from Earth in the Constellation Orion. It is in a region of space undergoing active star formation - something Herschel has been most keen to study. The Hubble space observatory has also returned to the Horsehead scene, to celebrate 23 years in orbit. Together, these two great facilities give scientists a much broader insight into what is taking place in this familiar patch of the heavens. Sentences rarely exist in isolation. Coherence holds text together. Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 4 / 20
Outline 1 Discourse 2 Relevant linguistic concepts Computational approaches 3 Coherence 4
Relevant linguistic concepts Important concepts from linguistics • Genre • Discourse modes • Information structure Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 6 / 20
Relevant linguistic concepts Genre • Text-level analysis • Genre influences various aspects of texts • Structure • Themes and topics (but != domain) • Choice of vocabulary • Linguistic register/style • .... • Many different classification schemes Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 7 / 20
Relevant linguistic concepts Discourse modes • Text-passage level analysis • Following Smith 2004 Modes of Discourse : • Narrative • Description • Report • Information • Argument • Discourse modes “do coherence” in different ways Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 8 / 20
Relevant linguistic concepts Information structure (IS) • Sentence/phrase-level analysis , but with respect to previous discourse • Entities and situations classified as GIVEN , OLD , NEW • IS interacts with phonology & syntax (at least) and matters for coherence Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 9 / 20
Outline 1 Discourse 2 Relevant linguistic concepts Computational approaches 3 Coherence 4
Computational approaches Some active research areas in CL • Coreference resolution • Centering theory and lexical chains • Topic modeling and document structure • Discourse relations and discourse structure Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 11 / 20
Computational approaches Coreference resolution • Entity-level analysis • Linking references to common entities • Cues: anaphoric expressions • pronouns • demonstratives (e.g. this movie ) • alternate forms of reference ( President Obama, Barack Obama, Obama, President of the US ) Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 12 / 20
Computational approaches Centering theory • Local analysis (words/phrases in pairs of clauses/sentences) • Relationships between entities in adjacent utterances • Coreference is an essential component Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 13 / 20
Computational approaches Lexical chains • Local analysis (words/phrases) , but with aim at global analysis • Semantic relatedness between nouns, verbs, adjectives • Often modeled using WordNet Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 14 / 20
Computational approaches Topics and structure • Text/text-passage level analysis • Concerned with aboutness • Topics used to model structure • Topic models ~ underlying topics defined in terms of which words are used • Topic transitions often co-occur with document-internal boundaries • Unsupervised models perform well Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 15 / 20
Computational approaches Discourse relations and structure • Clause/sentence/EDU-level analysis • Relations between clauses: causality, temporal structure, etc. • Higher-level structure: discourse parse for entire texts • Resources: corpora • Penn Discourse Treebank (PDTB) • Rhetorical Structure Theory (RST) Bank • DISCOR: texts labeled with SDRT structures Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 16 / 20
Computational approaches Introductory readings on discourse • Bonnie Webber and Aravind Joshi, Discourse Structure and Computation: Past, Present, and Future. ACL 2010 (http://homepages.inf.ed.ac.uk/bonnie/final_discourse_50.pdf) • Bonnie Webber, Marcus Egg, and Valia Kordoni, Discourse structure and language technology , NLE vol. 18, no. 4, 2012: especially section 4 on potential applications Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 17 / 20
Outline 1 Discourse 2 Relevant linguistic concepts Computational approaches 3 Coherence 4
Coherence Coherence • Our focus for the semester • Theories of coherence • Ways of modeling coherence • Applications Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 19 / 20
Coherence Text puzzle • Put the text in order • Note difficult decisions • What aspects of the text influence your decisions? Alexis Palmer (CoLi Saarland) What is discourse? 22 April 2013 20 / 20
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