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