Semantic Analysis

• Assigning meanings to the structures created by syntactic analysis.

• Mapping words and structures to particular domain objects in way consistent with

our knowledge of the world.

• Semantic can play an import role in selecting among competing syntactic analyses

and discarding illogical analyses.

– I robbed the bank -- bank is a river bank or a financial institution

• We have to decide the formalisms which will be used in the meaning

representation.

Ambiguity and Disambiguation

• Which knowledge representation will be used depends on the application --

Machine Translation, Database Query System.

• Requires the choice of representational framework, as well as the specific

meaning vocabulary (what are concepts and relationship between these concepts

-- ontology)

• Must be computationally effective.

• Common representational formalisms:

– first order predicate logic

– conceptual dependency graphs

– semantic networks

– Frame-based representations

Discourse Understanding

• Discourses are collection of coherent sentences (not arbitrary set of sentences)

• Discourses have also hierarchical structures (similar to sentences)

• anaphora resolution -- to resolve referring expression

– Mary bought a book for Kelly. She didn’t like it.

• She refers to Mary or Kelly. -- possibly Kelly

• It refers to what -- book.

– Mary had to lie for Kelly. She didn’t like it.

• Discourse structure may depend on application.

– Monologue

– Dialogue

– Human-Computer Interaction