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CPE 480 Natural Language Processing

Lecture 6: Semantics--From words to sentences to idioms

Asst. Prof. Nuttanart Facundes, Ph.D.

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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?

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4 Representation Approaches

• First-Order Predicate Calculus• Semantic Networks• Conceptual Dependencies• Frame-Based Representations

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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

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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

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Problems with FOPC

• Hard to represent beliefs• For example: I believe that Mary ate

British food.

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Principle of Compositionality (Frege)

• The meaning of a sentence is composed by the meaning of its parts

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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

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Solution: Lambda Calculus

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Different Sentences

• Declarative: Flight 487 serves lunch.• Imperative: Serve lunch.• Yes/No Questions: Does Flight 207 serve

lunch?• Wh-Questions: Which flights serve lunch?

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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

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