semantic analysis waes3303 rohana [email protected]
TRANSCRIPT
Representing Meaning
The meaning of linguistics utterances can be captured in formal structures is called meaning representation.
Context-independent sense : meaning Context-dependent aspects : usage The representation of context-independent
meaning is called Logical Form (*modularity)
Everyday tasks
Consider the following everyday language tasks that require some form of semantic processing: Answering an essay question in exam Realizing that you’ve been insulted Learning to use a new piece of software by reading the
manual Deciding to order at a restaurant by reading a menu Following a recipe
Semantic Analysis
The tasks require access to representations that link the linguistic element involved in the task to the non-linguistic knowledge of the world needed to successfully accomplish the tasks.
We take linguistics input and construct meaning representations that are made up of the same kind of stuff that is used to represent this kind of everyday commonsense knowledge of the world.
The process whereby such representations are created and assigned to linguistics inputs is called Semantic Analysis.
Semantic Interpretation
The process of mapping a sentence to its LF = Semantic Interpretation
The process of mapping the LF to the final KR language = Contextual Interpretation
KR language: FOPC, Semantic Net, Frame-based, Conceptual Dependency
Use symbols= correspond to objects and relation among objects
LF
2 approaches: 1. LF is defined as the literal meaning of the
utterance & LF is the same as the KR. LF must allow indexical terms, that is, terms that are
defined by KR (eg. Pronoun, definite) 2. If LF is not part of the KR – uses the notion of a
Situation, which is a particular set of circumstances in the world.
LF
Language creates special types of situations based on what information is conveyed.
Show example 8.1, 8.2 Allen pg 230
Word Senses and Ambiguity
Semantic unit = morpheme/ word? No because of the presence of ambiguity (eg. ‘go’ has > 40 entries in a dictionary)
A word – has one or more senses The different senses can be organized into a set of
broad classes of objects by which we classify the world. The set of different classes of objects in a representation
is called Ontology. To handle a Natural Language, we need a much broader
ontology than the one found in formal logic.
Classification of objects
Classification of objects, Aristotle suggestions: substance(physical object), quantity(such as Numbers), quality (such as bright red), relation, place, time, position, state, action and affection.
Other classes: events, ideas, concepts and plans. 2 of the most influential classes:
Events: things that are happen in the world (Important because they provide the structure for organising the interpretation of sentences)
Actions: things that agents do, thus causing some events Situations: refers to some particular set of circumstances &
can be viewed as subsuming the notion of events. May act like an abstraction of the world over some location and time.
Ambiguity
A word is semantically ambiguous if it maps to more than one sense
Virtually, all senses involve some degree of vagueness
Example: page 232 (kid/ horse/ kiss/ ran)
Thematic Roles (cases)
Semantic roles (actor/ object/ instrument) Introduce relations such as AGENT, THEME
and INSTR to capture the intuitions