Languages: Natural and Formal

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CC 2007, 2011 attribution R.B. Allen

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?



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)


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



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.

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

S

NP+VP

NP

N, Adj+N,

VP

V, V+NP

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,



S

NP

VP

N

V

NP

Adj

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.


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.

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?





CC 2007, 2011 attribution R.B. Allen

Beyond Traditional Dictionaries:

WordNet and FrameNet


WordNet

http://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
.





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.





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.




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


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
)




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


Claim

Grounds

Rebuttal

Evidence

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.


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”?


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



How close to Passing the Turing Test?


Chatterbots


IBM “Watson” plays Jeopardy.

CC 2007, 2011 attribution
-

R.B. Allen

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.

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