This lecture introduces pragmatics: that's the study of how the message that a speaker conveys when he utters or writes down some natural language sentence or sentences is influenced by context, and consequently, since contextual information is hidden, decoding the speaker's intended message is uncertain and subject to revision should subsequent contrary evidence about what he or she meant be observed. We're going to look at a particular approach to modelling pragmatic aspects of natural language understanding: namely the role of discourse coherence.
Coherence-based theories of discourse assume that when someone says something, it's semantically related in some way to the context in which it's said (ie, it's not a non-sequitor, or completely irrelevant), and identify that semantic relationship and resolving the speaker's intended meaning are logically co-dependent. Furthermore, these theories assume that the semantic relationships among the sentences in a text or dialogue, which are known as coherence relations, impose a hierarchical structure on the discourse, which in turn models what's salient in the context and what isn't, and so constrains the coherent moves that a speaker can make next.
Coherence relations model things that people do with their utterances to connect them to something salient in the context: they continue a narrative, they provide background information, they draw out resemblences and contrasts with some prior salient content, they answer questions, they correct prior assertions, and so on. These coherence relations constrain the semantic content of the contents of the discourse segments that they connect together, and in doing so yield inferences about speaker meaning that goes beyond the lexical and compositional semantics of the NL utterances the speaker used.
Lecture 19 Slides: Whole!
19a: Discourse Coherence
- Slides: 19a_slides.pdf
19b: Representing Discourse Coherence
- Slides: 19b_slides.pdf
19c: Computing Discourse Coherence
- Slides: 19c_slides.pdf
Required Reading
J&M chapter 27 (2nd edition chapter 21.2--21.5)
NOTE: The abbreviation J&M refers to the textbook:
Dan Jurafsky and James H. Martin, Speech and Language Processing.
When we specify 2nd edition, we are referring to the version of the book that was published by Pearson International in 2008.
When we specify 3rd edition, then we will supply links to the drafts of the relevant parts of that book (since the third editiion isn't published yet, but the current draft is available here).
Quiz: Discourse Coherence
These questions are designed to test your understanding of the above course content; doing this quiz does not contribute to your overall grade. Some questions require a text answer. You can ask for formative feedback on these from your tutor or on piazza. Other questions are multiple choice or they require a numeric answer: you will get immediate feedback for these. Please don't attempt this quiz until you have acquainted yourself with this lecture and the required reading.
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