CPE 480 Natural Language Processing

1. CPE 480 Natural Language Processing Lecture 6: Semantics--From words to sentences to idioms Asst. Prof. Nuttanart Facundes, Ph.D.

2. Theories of Meaning • Words have different meaning, depending on the context in which they are used • What is the meaning of a word? • How can we represent the meaning? • What formalisms can be used?

4. 4 Representation Approaches • First-Order Predicate Calculus • Semantic Networks • Conceptual Dependencies • Frame-Based Representations

5. Correspondences between representations • They all share a common foundation:  meaning representation consists of structures composed of sets of symbols Symbol Structures  are objects and relations among objects

6. Meaning structure of language • Various ways by which human language conveys meaning • Form-meaning associations • Word-order regularities • Sense systems • Conjunctions and quantifiers • Predicate-argument structure

9. Problems with FOPC • Hard to represent beliefs • For example: I believe that Mary ate British food.

14. Principle of Compositionality (Frege) • The meaning of a sentence is composed by the meaning of its parts

16. Semantic Augmentations to Context-Free Grammars • Augmenting context-free grammar rules with semantic attachments • Attachments = Instructions that specify how to compute the meaning representation of a construction from the meanings of its consistent parts

18. Solution: Lambda Calculus

19. Different Sentences • Declarative: Flight 487 serves lunch. • Imperative: Serve lunch. • Yes/No Questions: Does Flight 207 serve lunch? • Wh-Questions: Which flights serve lunch?

20. The Role of Sentences • Declarative  intended to convey factual information • Imperative  request for an action • Yes/No Questions  request for affirmative/negative answer • Wh-Questions  request for information