Natural Language Natural Language ProcessingProcessing

Daniele QuerciaDaniele Quercia

Fall, 2000Fall, 2000

Presentation Presentation Outline

• Introduction to the Natural Language Processing (NLP)

•Applications of NLP

•Discussion

Introduction to Natural Introduction to Natural Language Processing Language Processing

(NLP)(NLP)

NLPNLP

•What is Natural Language processing (NLP)?

•“The Natural Language Processing (NLP) is the engineering of systems that process or analyse written or spoken natural language.”

NLP System

(computational model)

Natural Language(English)

Representation

of the input meaning

Related disciplinesRelated disciplines

Linguistics

Computer Science

Psychology Neuroscie

nce Natural Language Processing

Knowledge of languageKnowledge of language

These language processing applications use knowledge of language

Unix wc program› total number of bytes, words, lines in a text file.

What is a word?

A possible file: PIPPO.TXT

Hallo Pippo. Ciao Pippo. Auf widersehen Pippo.

Knowledge of language - 2Knowledge of language - 2

Types of knowledge used in NLP

Phonetics and Phonology Morphology Syntax Semantics Pragmatics Discourse

NLP can be viewed as resolving ambiguity at one of these levels.i

Knowledge of language - 3Knowledge of language - 3

Example: HAL computer system.capable of interacting with humans

Stanley Kubrik’s film 2001: A Space Odissey

Conversation between HAL and Dave

Knowledge of language - 4Knowledge of language - 4

Example(cont’d): HAL computer system.capable of interacting with humans

Stanley Kubrik’s film 2001: A Space Odissey

Dave: Open the pod bay doors, right now. HAL: I’m sorry Dave, I’m afraid I can’t do that.

Knowledge of language - 5Knowledge of language - 5

Phonetics and Phonology

The study of linguistic soundsHow word are pronounced in colloquial speech

Syntax

The study of the structural relationship between wordsbut syntax don’t tell us much about the meaning …

e.g. :I saw the Grand Canyon flying to New YorkTime flies like an arrow

Knowledge of language - 6Knowledge of language - 6

Semantics

The study of meaning

e.g. :

I work for J.F. Zich and he’s a good boss which is a good company

Pragmatics

The study of how language is used to accomplish goals

e.g.

Can youn tell me what time is it?Could I have the salt?

Knowledge of language - 7Knowledge of language - 7

Morphology

The study of the meaningful components of words. e.g. :Kick, kicks, kicked, kicking Arm, army

Discourse

The study of linguistic linguistic units larger than a single utterance

Applications of NLPApplications of NLP

Applications of NLP Applications of NLP

· Text-based applications

· Dialogue based applications

Speech recognitio

n

Machine translatio

n

Information retrieval

Applications of NLP Applications of NLP

Machine translationAutomatic machine translation

translates texts from one language to another

Windows 98 must be delivered either without Internet Explorer or in connection with the sailor of the competitor Netscape

Windows 98 deve essere distribuito senza Internet Explorer o insieme al navigatore del concorrente Netscape

Important constraint

The text needs to be restricted

to a limited range of subjects

Applications of NLP Applications of NLP

Machine translation even the best system produces poor translation… … but Machine-assisted translation uses a computer to help a translator.

Applications of NLP Applications of NLP

Information retrievial

concerns the retrieving of relevant information from databases.

Applications of NLP Applications of NLP

Information retrievial (cont’d)

Inverted index

Retrieval depends only on how often each word appears in a document

Should we treat all words equally?

Applications of NLP Applications of NLP

Information retrievial (cont’d)

Stop list: words to ignoreMany frequent words in English are function words, which are useless.

Applications of NLP Applications of NLP

Speech recognition

Speech generation is comparatively easy, but recognition is hard !

The acoustic signal is highly ambigousDisambiguation using statistics

If …they buy… occurs more frequently than …they by …, it will chosen

ConclusionsConclusions

Conclusions Conclusions

Computers can process natural language in a variety of interesting ways

A computer can’t do anything close to “understanding” language …

NLP is almost never error-free

A very special thanks to …A very special thanks to …