1. Semantics
Going beyond syntax

2. Semantics Relationship between surface form and meaning
What is meaning?
Lexical semantics
Syntax and semantics

3. What is meaning? Reference to “worlds” Understanding Meaning as action
Objects, relationships, events, characteristics
Meaning as truth
Understanding
Inference, implication
Modelling beliefs
Meaning as action
Understanding activates procedures

4. Lexical semantics Meanings of individual words Grammatical meaning
Sense and Reference
What do we understand by the word lion ?
Is a toy lion a lion? Is a toy gun a gun? Is a fake gun a gun?
Grammatical meaning
What do we understand by the lion, lions, the lions, … as in
The lion is a dangerous animal
The lion was about to attack

5. Lexical relations
Lexical meanings can be defined in terms of other words
Synonyms, antonyms, broader/narrower terms
Part-whole relationships (often reflect real-world relationships)
Linguistic usage (style, register) also a factor

6. Semantic features
Meanings can be defined (to a certain extent) in terms of distinctive features
e.g. man = adult, male, human

7. Types of representation
1. Syntactic relations
The man shot an elephant with his gun
shot
subj obj adv
man elephant gun
det det mod
the an his

8. Types of representation
2. Deep syntax
The man shot an elephant with his gun
An elephant was shot by the man with his gun
shot
dsubj dobj instr
man elephant gun
qtf qtf poss
the an his

9. Types of representation
3. Semantic roles, deep cases
The man shot an elephant with his gun
An elephant was shot by the man with his gun
shot
agent patient instr
man elephant gun
qtf qtf poss
the an his
The man used his gun to shoot an elephant

10. Types of representation
4. Event representation, semantic network
The man shot an elephant with his gun
An elephant was shot by the man with his gun
shooting
shooter shot- instr
thing
man elephant gun
qtf qtf poss
the  man
The man used his gun to shoot an elephant

11. Uses for semantic representations
As a linguistic artefact (because it’s there)
To capture the text  meaning relationship
Identifying paraphrases, equivalences (e.g. summarizing a text, searching a text for information)
Understanding and making inferences (e.g. so as to understand a sequence of events)
Interpreting questions (so as to find the answer), commands (so as to carry them out), statements (so as to update data)
Translating

12. Uses for semantic representations
Different levels of understanding/meaning
Textual meaning may be little more than disambiguating
Attachment ambiguities
Word-senses
Anaphora (pronoun reference, coreference)
Conceptual meaning may be much deeper
Somewhere in between – a good example is Wilks’ preference semantics: especially good for metaphor

13. Linguistic issues Words and Concepts
Objects, properties, actions  n, adj, v
Language allows us to be vague (e.g. toy gun)
Semantic primitives – what are they?
Meaning equivalence – when do two things mean the same?
Grammatical meaning
Tense vs. time
Topic and focus
Quantifiers, plurals, etc.

14. Linguistic issues
There are many other similarly tricky linguistic phenomena
Modality (could, should, would, must, may)
Aspect (completed, ongoing, resulting)
Determination (the, a, some, all, none)
Fuzzy sets (often, some, many, usually)

15. Lexical semantics
Lexical relations (familiar to linguists) have an impact on NLP systems
Homonymy –word-sense selection; homophones in speech-based systems
Polysemy – understanding narrow senses
Synonymy – lexical equivalence
Ontology – structure vocabulary, holds much of the “knowledge” used by clever systems

16. Neuro-linguistic programming