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Languages: Natural and Formal. Definition In math and computer science: A lexicon & rules for combining terms from the lexicon In common use: Structured verbal interaction between people Any structured interaction such as “The Language of Film”

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Languages: Natural and Formal

CC 2007, 2011 attribution R.B. Allen

language
Definition

In math and computer science:

A lexicon & rules for combining terms from the lexicon

In common use:

Structured verbal interaction between people

Any structured interaction such as “The Language of Film”

Are computer languages a model for human natural language?

Language

CC 2007, 2011 attribution R.B. Allen

wide variability among natural languages
Sentence Structure

SVO (Subject-Verb-Object) (English, Chinese)

OVS (Gaelic/Celtic)

SVO (Hindi, Japanese, Hopi)

Written

Ideographic (Chinese),

Syllabic (Thai),

Alphabetic (English)

Spoken

Tonal (Chinese)

Non-tonal (English)

Wide Variability among Natural Languages

CC 2007, 2011 attribution R.B. Allen

layers of natural language
Words

Morphology, Orthography, Phonetics, Phonology

Syntax

Phrase and sentence structure based on parts of speech

Semantics

Literal meaning

Pragmatics/Discourse

Uses beyond the literal meaning

Layers of Natural Language

CC 2007, 2011 attribution R.B. Allen

grammars
Grammars are most often associated with modeling syntax though semantic grammars are also possible. In the broadest sense, grammars are rules for languages

The most general grammars are “context-free”. That is, the structure does not depend of the context.

The grammars used for natural language syntax are usually “constituent grammars”. That is they identify the relationship of the components (constituents) of the phrase.

Grammars taught in grade school are “descriptive” grammars. Grammars in the formal analysis of language are “prescriptive” and usually “generative”.

Grammars are usually defined by rules, but statistical transition networks are also used to model the structure of language.

Grammars

CC 2007, 2011 attribution R.B. Allen

modeling natural language syntax with grammars
Rewrite (or production) rules (phrase-structure grammar)

A very simple example of rewrite rules

Modeling Natural LanguageSyntax with Grammars

CC 2007, 2011 attribution R.B. Allen

parsing
Can we identify the grammatical structure of a given statement?

Parsing is the basis of syntax checking for computer program compilers.

A parse tree is structure of a given statement given

a lexicon with parts-of-speech

a grammar

A very simple sample parse tree

shown at the right. This has

a Verb Phrase with a Direct Object.

This Direct Object is itself a Noun

Phrase.

Difficulties: Garden path sentences

“The man who hunts ducks out on weekends”

Many algorithms have been developed for parsing,

Parsing

S

NP

VP

NP

Adj

N

V

Adj

N

CC 2007, 2011 attribution R.B. Allen

psycholinguistics
How do people process and learn language?

Chomsky’s claims for formal (discrete) grammars:

All natural languages are context free

Children have grammatical rules wired in:

“I goed to the store.”

Competence vs. performance

People know what is grammatically correct even if they make errors.

Transformational grammars describe rules for re-arranging of structure such as forming a question from a declarative sentence.

An alternative to discrete (formal) grammars is statistical (approximate) grammars. These can be learned by association.

Psycholinguistics

CC 2007, 2011 attribution R.B. Allen

modeling syntax with statistical models
While most grammars are a rule-based representation, a statistical representation of language may m capture structure more flexibly.

In particular, Markov models can describe the transitions between different parts of speech. For instance, the Nouns are often followed by Verbs but Adjectives are rarely followed by Verbs.

Modeling Syntax with Statistical Models

CC 2007, 2011 attribution R.B. Allen

words
What exactly is a word? (also matters for the design of search engines)

Sail-boat, Pennsylvania, 555-1212, F-16

Definitions of words

Why aren’t the definitions of words in dictionaries all the same?

Are exact definitions of words possible?

Across time, across groups

How do words evolve in meaning?

Sometimes by radial categories (that is, often by metaphor)

What is the relationship between concepts and words?

Words

CC 2007, 2011 attribution R.B. Allen

beyond traditional dictionaries wordnet and framenet
WordNethttp://wordnet.princeton.edu/

Shows hierarchical relationships for dictionary terms. Very loosely, this can be thought of as an ontology.

FrameNet http://framenet.icsi.berkeley.edu/

Shows the elements usually associated with a concept.

For verbs show the relationship among concepts. For instance “to give” implies that there is a gift, a gifter, and a giftee.

Beyond Traditional Dictionaries:WordNet and FrameNet

CC 2007, 2011 attribution R.B. Allen

semantics
Very different surface structures can have similar semantics.

The semantics of natural language is often judged by the meaning and relationship of the components. Subjective and contextualized meaning is considered as pragmatics which we will discuss later.

The semantics of statements in a computer programming language (i.e., a program) can be determined from its behavior.

Semantics

CC 2007, 2011 attribution R.B. Allen

representing semantics
Semantic grammars

Even with different surface structure, can we develop a standard representation for the meaning.

Interlingua

A common representation for meaning across languages. This could be useful for translation.

Representing Semantics

CC 2007, 2011 attribution R.B. Allen

pragmatics social uses of language
Pragmatics extends the literal semantics to consider other ways language is used.

Referential

Conveys information about some real phenomenon

This is what we think about as normal language use

Expressive

describes feelings of the speaker

Conative

attempts to elicit some behavior from the addressee

Phatic

builds a relationship between both parties in a conversation

Meta-lingual

self-references

Poetic

focuses on the text independent of reference

from R. Jakobson

Pragmatics: Social Uses of Language

CC 2007, 2011 attribution R.B. Allen

discourse
Sentences form macro-structures or super-structures of meaning. This includes structured language such as argumentation, negotiation, news, narrative, and explanations.

What are the components (elements) and structure of discourse. For instance, structuring messages to make it clear for listeners.

Given-New

Bill (a person you know) went to the store (is in a new location)

Theme-Rheme

When in Rome (theme), do as the Romans do (rheme)

Discourse

CC 2007, 2011 attribution R.B. Allen

argumentation
Toulmin has proposed a general structure for arguments

There are a lot of complex structured verbal interactions

Legal arguments

Design rationale

Negotiations

Argumentation

Grounds

Claim

Evidence

Rebuttal

CC 2007, 2011 attribution R.B. Allen

explanations and causation
An explanation consists of

Two types of phenomena being explained

Causal antecedents

How do we explain the American Civil War?

Sub-processes

How does a gasoline engine work?

Background for the person receiving the explanation needs to be considered.

Explanations and Causation

CC 2007, 2011 attribution R.B. Allen

stories and narrative
(Goals + Events + Resolution) + Characters

Many stories seem highly structured

Some stories seem so structured that they have been described as “story grammars”. This is most notably true of Russian Fairy Tales

Many stories also reflect familiar human quandaries

“Romeo and Juliet”

Interactive and dynamic narrative (useful in games)

Could we become a player in an interactive “Romeo and Juliet”?

Stories and Narrative

CC 2007, 2011 attribution R.B. Allen

conversation
Conversation adds a social and interactive component to language

Conversational norms (Maxims)

Truthful, informative, relevant, clear

But these are routinely violated.

e.g. shaggy dog stories.

Managing conversations

Opening / Closing

Turn taking

Conversation

CC 2007, 2011 attribution R.B. Allen

how close to passing the turing test
How close to Passing the Turing Test?
  • Chatterbots
  • IBM “Watson” plays Jeopardy.

CC 2007, 2011 attribution - R.B. Allen

natural language processing nlp
We will revisit natural language in a few weeks when we look at the use of natural language in information systems.Natural Language Processing (NLP)

CC 2007, 2011 attribution R.B. Allen

formal languages
Formal Languages
  • Programming languages
    • High-level languages (e.g., C++) are built to simplify the use of low-level machine language
    • Debugging tools typically check syntax but not semantics

CC 2007, 2011 attribution - R.B. Allen