Introduction to Arabic NLP

8/21/2019 Introduction to Arabic NLP

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Introduction to ArabicNatural Language Processing

Nizar HabashColumbia University

Center for Computational Learning [email protected]

MEADR 2009Cairo, Egypt

April 21, 2009

CADIM


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• Focus of this

tutorial

– Phenomena – Concepts – Approaches

– Resources• What is ‘Arabic’? – Arabic Script – Arabic Language

• Modern StandardArabic (MSA)

• Arabic Dialects


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Road Map• Introduction

• Orthography

• Morphology

• Syntax


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Road Map• Introduction• Orthography

– Arabic Script

– MSA Phonology and Spelling

– Recognizing Arabic vs. Persian/Urdu/Pashto/Kurdish/Sindhi/… – Encoding Issues

• Morphology

• Syntax


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Arabic Script


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Arabic ScriptArabic script is an alphabet with allographic variants,

optional zero-width diacritics and common ligatures.

Arabic script is used to write many languages: Arabic,Persian, Kurdish, Urdu, Pashto, etc.

رعلا ُطَخلا


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Arabic ScriptAlphabet

• letter forms

• letter marks

• Arabic only

• Other languages

• Persian, Kurdish,Urdu, Pashto, etc.

• OCR output ambiguity; common spelling errors


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Arabic Script

/b/

Alphabet (MSA)

• letters (form+mark)

• Distinctive

• Non-distinctive

/t/

ث

/θ/

س

/s/

ش

/ʃ/

/ʔ/glottal stop aka hamza

ؤا ئ


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Arabic ScriptLetter Shapes

• No distinction between print and handwriting• No capitalization• Right-to-left• Ambiguous

shapes• Connectiveletters

• Disconnective

letters( ة ى رزد ذ و ؤ ا )cause word-internal visualspacing

ز

ن

final

medial

initial

Stand

alone

غ


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Arabic ScriptLetter shaping

/k itāb /آ =بآ تك k tābbook

/k atab /

آ =آ تك

k tbto write


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Arabic Script

/bin/

/bun/

/ban/

NunationDiacritics

• Zero-width characters

• Used for short vowels

آ /katab/ to write

• Nunation is used for

nominal indefinitemarker in MSA

آ ب /kitābun/ a book

/bi/

/bu/

/ba/

Vowel


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Arabic Script

/bb/

DoubleConsonant

/bban/

/bbin//bbu/

Diacritics

• No-vowel marker (sukun)

/maktab/ office

• Double consonant marker (shadda)

آ /kattab/ to dictate • Combinable

/b/

No Vowel


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Arabic Script

ب=َ ب ع َر َب

Putting it together

Simple combination

Ligatures ب=ْ ب

غ َر ْب West /ʁarb/

Arab /ʕarab/

م

م

ل

/Peace /salāmس

م


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Arabic ScriptTatweel

• ‘elongation’

• aka kashida

• used for text highlightand justification

االنس

حقوق

سـنالا

وق قـح

ـ ـ سـنالا

وق ـ ـ قـح

ـ ـ ـ ـ سـنالا

وق ـ ـ ـ ـ قـح

human rights /ħuqūq alʔinsān/


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Arabic Script• Different styles

• High fluidity• Optional ligatures

• Verticalarrangements

/alʤabr / /muħammad / /ʕarabi/

ع بيمحمدالج

محمالج ع

عريبحمماجلرب

algebraMuhammadArabic


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٠

0

٩Eastern Indo-ArabicIran, Pakistan, etc.

٩

Indo-ArabicMiddle East

987654321Western Arabic

Tunisia, Morocco, etc.

Arabic Script “Arabic” Numerals• Decimal system• Numbers written left-to-right in right-to-left text

الفرنس 132بعد1962استقلت اجلزائر يف سنة . عاما من االحتالل

Algeria achieved its independence in 1962 after 132 years of French occupation.

• Three systems of enumeration symbols that vary by region


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• Orthography – Arabic Script

– MSA Phonology and Spelling


• Morphology

• Syntax


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MSA Phonology and Spelling• Phonological profile of Standard Arabic

– 28 Consonants – 3 short vowels, 3 long vowels, 2 diphthongs

• Arabic spelling is mostly phonemic … – Letter-sound correspondence

ā ʔt bʤ θx ħδ dz r ssʖ ʃtʖ dʖʕk ʁq f lm

ولقخحج ى ؤء

h nw j ū ī δ


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MSA Phonology and Spelling• Arabic spelling is mostly phonemic …

Except for • Medial short vowels can only appear as

diacritics

• Diacritics are optional in most written text – Except in holy scripture – Present diacritics mark syntactic/semantic

distinctions

• آ /katab/ to write آ /kutib/ to be written• /ħubb/ love /ħabb/ seed• Dual use of ,ا ,و ي as consonant and long vowel

ا – (/‘/,/ā/) و (/w/,/ū/) ي (/j/,/ī/)


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MSA Phonology and Spelling• Arabic spelling is mostly phonemic …

Except for (continued)

• Morphophonemic characters

– Feminine markerة

(ta marbuta)• آ /kabīr/ (big ♂) آ /kabīr a/ (big ♀)

– Derivation marker

• /ʕasa/ (to disobey ) (a stick )• Hamza variants (6 characters for one phoneme!)

– ) ء أإؤئ) /baha’/ + 3MascSing (his glory)


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MSA Phonology and Spelling• Arabic spelling can be ambiguous

– optional diacritics and dual use of letter • But how ambiguous? Really?• Classic example

ths s wht n rbc txt lks lk wth n vwls

this is what an Arabic text looks like with no vowels• Not exactly true

– Long vowels are always written

– Initial vowels are represented by an ‘alef’

– Some final short vowels are represented

ths is wht an Arbc txt lks lik wth no vwls

Will revisit ambiguity in more detail again under morphology discussion


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Proper Name Spelling• The Qadafi-Schwarzenegger problem

– Foreign Proper name spelling is often ad hoc – Multiplicity of spellings causes increased sparsity

Schwarzenegger

زرا

زرازرا

ار

Gadafi Gaddafi Gaddfi GadhafiGhaddafi Kadaffy Qaddafi Qadhafi …

ا


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• Orthography – Arabic Script – MSA Phonology and Spelling


• Morphology

• Syntax


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Arabic ScriptOther languages

Arabic

• No more than 3 dots• Dots either above or below• Marks are 1/2/3 dots, hamza (ء)

or madda (~) only• Rare borrowing for foreign words

•,/ /pپ ,/ /vڤ ڤ گ ,/ /gچ / /tʃچ

• regionally variable

Not Arabic• Extra marks: haft (v), ring (o), taa ,(ط)

four dots (::), vertical dots (:)• Some Numerals (,,)

Once you learn the alphabet, it is easier ☺

ړ ژڈ

ڐ

ۅ څ ځڈ

…گ ێ ڤ

أ إ ؤئ ة ت ث ج ح خ

ر ذ ز

ش ص

ض ط ظ ع غ ف

ق ك ل م ن وى ي ء


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Arabic

Not Arabic


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Arabic

Not Arabic

... ا...

ا ن رو او

و

... ا... وا رق اح

او او ر ا واا ا

ا ا ا وا ط و ا ام

... :ورد د


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Arabic

Not Arabic


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Encoding Issues• Encoding Arabic

– Data entry, storage, and display – Ease of use for Arabic-illiterate users – Multi-script support – Multilingual support (extended Arabic characters)

• Types of Encoding – Machine character sets

• Graphemic (shape insensitive, logical order)• Allographic (shape/direction sensitive) [obsolete]

– Human accessible• Transliteration• Phonetic spelling (IPA)• Romanization


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Encoding Issues• Many Conflicting Character Sets for Arabic


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Encodings• CP-1256

– Commonly used – 1-byte characters

– Widely supportedinput/display

– Minimal support forextended Arabiccharacters

– bi-script support(Roman/Arabic)

– Tri-lingual support:Arabic, French,English (ala ANSI)


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Encodings• Unicode

– Becoming thestandard more andmore

– 2-byte characters

– Widely supportedinput/display

– Supports extendedArabic characters

– Multi-scriptrepresentation


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Encodings• Unicode

– Supports presentationforms (shapes andligatures)


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Encoding IssuesArabic Display

• Memory (logical order)

ÔÇÑßÊ ÝáÓØíä (Palestine) Ýí ÇæáãÈíÇÏ (Olympics) 2000 æ 2004.

ر ك ت ف ل س ين (Palestine) يف و ل م ب ي د (Olympics) 2000 و 2004.

or this way for those with direction-bias

.4002 æ 0002 )scipmylO( ÏÇíÈãáæÇ íÝ )enitselaP( äíØÓáÝ ÊßÑÇÔ

.4002 و 0002 )scipmylO( في ولمبي د )enitselaP( ركت فلسين


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Encoding IssuesArabic Display

• Memory (logical order)ÔÇÑßÊ ÝáÓØíä (Palestine) Ýí ÇæáãÈíÇÏ (Olympics) 2000 æ 2004. ر ك ت ف ل س ين (Palestine) يف و ل م ب ي د (Olympics) 2000 و 2004.

• Display (visual order) – Bidirectional (BiDi) support• Numbers and Roman script. 2004و2000 (Olympics) في ولمبي د (Palestine) سين ل ف ت ك ر

– Letter and ligature shaping. 2004و2000 (Olympics) ود (Palestine) آر


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Display Problems

ï»¿ØªØ¯Ø´ÙŠÙ†Ù…Ù†Ø·Ù‚Ø©Ø-Ø±Ø© ÙÙŠØ¯Ø¨ÙŠÙ„Ù„ØªØ¬Ø§Ø±Ø©Ø§Ù„Ø§Ù„ÙƒØªØ±ÙˆÙ†ÙŠØ©

ÊÏÔêæ åæ×âÉ ÍÑÉáê ÏÈê ääÊÌÇÑÉÇäÇäãÊÑèæêÉ

ÊÏÔíä ãäØÞÉ ÍÑÉÝí ÏÈí ááÊÌÇÑÉÇáÇáßÊÑæäíÉ

د ور

؛

ُ

ع

ع

ع ع ع - عع

ع

ع

ع

،

ع

ع

ع

ع

ع

ع

ï» ؟ ¯ ´ ٹ †ظ

…†·‚ © -± © ط

ٹ

¯ ¨ٹ

ظ

„„ ¬§± © „§„§ط ƒ

±ˆ† ٹ

©

ʏʏʏʏ栥既栥既栥既栥既

ɠɠɠɠ ɠɠɠɠψ

ǑɠɠɠɠǤǤ㊑㊑㊑㊑親親親親ɠɠɠɠ

د ور

×â و هê ش

êل êدب êو èر

ʏʏʏʏ ɠɠɠɠ ɠɠɠɠψǑɠɠɠɠǡǡǡǡǡǡǡǡѦѦѦѦ

آ ف ر دب

د ور

WesternUnicodeISO-8859CP-1256Display Encoding

C P - 1 2 5 6

I S O - 8 8 5 9

U n i

c o d e

A c t u a l E n c

o d i n g

• Wrong encoding • Partial support problems


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س م م

Encoding IssuesArabic Input• Standard graphemic keyboard

• Logical order input


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EncodingsBuckwalter Encoding• Romanization

– One-to-one mappingto Arabic script spelling

– Left-to-right – Easy to learn/use – Human & machine compatible

• Commonly used in NLP – Penn Arabic Tree Bank

• Some characters can bemodified to allow use with XMLand regular expressions

• Roman input/display• Monolingual encoding (can’t do

English and Arabic)• Minimal support for extended

Arabic characters


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• Orthography• Morphology

• Syntax


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Morphology• Type

– Concatenative: prefix, suffix, circumfix – Templatic: root+pattern

• Function

– Derivational• Creating new words• Mostly templatic

– Inflectional• Modifying features of words

– Tense, number, person, mood, aspect

• Mostly concatenative


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– Derivational Morphology – Inflectional Morphology – Morphological Ambiguity – Arabic Computational Morphology

• Syntax


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Derivational Morphology• Templatic Morphology

b

م

kt

آ

ا

maktū bwritten

k āti bwriter Lexeme.Meaning =

(Root.Meaning+Pattern.Meaning)*Idiosyncrasy.Random

ك

maū āi

• Root

• Pattern

• Lexeme


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Derivational MorphologyRoot Meaning

• ك KTB = notion of “writing”

آ /katab/

write

آ /kātib/writer

ب /maktūb/

letter

آب /kitāb/

book /maktaba/

library

/maktab/

office

ب /maktūb/

written


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laHm

• LHM-1

• Notion of “meat” – /laħm/

• Meat

– م /laħħām/• Butcher


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• LHM-2

• Notion of “battle” – /malħama/

• Fierce battle

• Massacre• Epic

D i i l M h l


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• LHM-3

• Notion of “soldering” – /laħam/

• Weld, solder, stick, cling

– ا /iltaħam/• Be welded/soldered/fused

– /multaħim/• Welded, soldered, fused


D i ti l M h l


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Derivational MorphologyPattern Meaning

ask/make_writektb AistaktabRequirement Aista12a3X

Turn red/blushHmr AiHmarrTransformation Ai12a33IX

registerktb AiktatabAcquiescence, exaggeration Ai1ta2a3VIII

subscribe/enrollktb AinkatabPassive of Pattern I Ain1a2a3VII

correspondktb takaAtabReflexive of Pattern IIIta1aA2a3VI

learnElm taEal~amReflexive of Pattern IIta1a22a3V

seat jls AjlasCausation Aa12a3IVcorrespond with

ktb kaAtabInteraction with others1aA2a3III

dictatektb kattabIntensification, causation1a22a3II

writektb katabBasic sense of root1a2a3I

GlossExamplePattern MeaningPattern

• Verb Pattern Meaning is hard to define


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– Derivational Morphology – Inflectional Morphology – Morphological Ambiguity – Arabic Computational Morphology

• Syntax


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Inflectional Morphology• Derivational Morphology

– Lexeme ≈ Root + Pattern

• Inflectional Morphology – Word = Lexeme + Features

• Part-of-speech

– Traditional : Noun, Verb, Particle – Computational : N, PN, V, Adj, Adv, P, Pron, Num,Conj, Det, Aux, Pun, IJ, and others

– Many tag sets exist ranging from 3 to over 22K tags

• Noun-specific Features• Verb-specific Features• Other Features


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Inflectional Morphology• Noun-specific Features – Number: singular, dual, plural, collective – Gender: masculine, feminine – Definiteness: definite, indefinite – Case: nominative, accusative, genitive – Possessive clitic

• Verb-specific Features – Aspect: perfective, imperfective, imperative – Voice: active, passive – Tense: past, present, future – Mood: indicative, subjunctive, jussive

– Subject (Person, Number, Gender) – Object clitic• Other Features

– Single-letter conjunctions – Single-letter prepositions

Inflectional Morphology


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Nouns

ت

/walilmaktabāt/

ات++ ا++ wa+li+al+maktaba+āt

and+for +the+library+plural

And for the libraries

conj prepnoun poss plural article

آ

/wakabiyūtinā/

+ ت + ك + wa+ka+ biyūt+nā

and+like+houses+our

And like our houses

• Morphotactics (e.g. ا+ل )• Arabic Broken Plurals (templatic)



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Verbs

ه

/faqulnāhā/

ه++ل+فfa+qul+na+hā

so+said+we+it

So we said it

conjverbobject subj tense

/wasanaqūluhā/

ه+++س+ wa+sa+na+qūl+u+hāand+will+we+say+it

And we will say it

• Morphotactics• Subject conjugation (suffix or circumfix)

I fl ti l M h l


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Inflectional Morphologykatab ‘to write’

• Perfect verb subject conjugation (suffixes only )

آ katabā آ katabtū

آ katabtum

آ katabnā

PluralDualSingular

آ kataba3

آ katabtumā آ katabta2

آ katabtu1

• Imperfect verb subject conjugation ( prefix+suffix )

Feminine form and other verb moods not shown

yaktubān ن yaktubūn

ن taktubūn naktubu

PluralDualSingular

yaktubu3

taktubān taktubu2آا aktubu1


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– Derivational Morphology

– Inflectional Morphology – Morphological Ambiguity – Arabic Computational Morphology

• Syntax


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Morphological Ambiguity

• Derivational ambiguity – : basis/principle/rule, military base,Qa'ida/Qaeda/Qaida

• Inflectional ambiguity – /taktub/: you write, she writes – Segmentation ambiguity

• و: he found; +و : and+grandfather • : + ل : for a language; ا+ ل : for the language


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Morphological Ambiguity• Spelling ambiguity

– Optional diacritics• آ: /kātib/ writer , /kātab/ to correspond

– Suboptimal spelling• Hamza dropping: ,أ ا

• Undotted ta-marbuta: ة • Undotted final ya:

ي

• Multiple sources of ambiguity

بني

– /bayyana/ Verb he demonstrated – /bayyanna/ Verb they [feminine] demonstrated – /bayyin/ Adj clear/evident/explicit – /bayna/ Prep between/among – /biyin/ Proper Noun in Yen

– /biyn/ Proper Noun Ben

Morphological Disambiguation


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in English

• Select a morphological tag that fullydescribes the morphology of a word

• Complete English morphological tag set

(Penn Treebank): 48 tagsVerb:

• Same as “POS Tagging” in English

goesgogonegoingwentgo

VBZVBPVBNVBGVBDVB



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• Morphological tag has 14 subtags

corresponding to different linguistic categories – Example:VerbGender(2), Number(3), Person(3), Aspect(3),Mood(3), Voice(2), Pronominal clitic(12),

Conjunction clitic(3)• 22,400 possible tags

– Different possible subsets

• 2,200 appear in Penn Arabic Tree Bank Part 1(140K words)• Example solution: MADA (Habash&Rambow 2005)


in Arabic

MADA (Habash&Rambow 2005)(Habash&Rambow 2007)

(Roth et al 2008)


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W-3 W-2 W-1 W0 W1 W2 W3 W4W-4

MORPHOLOGICALANALYZER

MORPHOLOGICALCLASSIFIERS

• Rule-based

• Human-created

• Multiple independentclassifiers

• Corpus-trained

2nd

3rd

5th

4th

1st

RANKER

• Heuristic orcorpus-trained

(Roth et al. 2008)

MADA(Habash&Rambow 2005)(Habash&Rambow 2007)

(Roth et al 2008)


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MADAMorphological Analysis and Disambiguation for Arabic

;;; SENTENCE AsbAnyA tnfy tjmyd AlmsAEdp AlmmnwHp llmgrb;;WORD AsbAnyA;;MADA: AsbAnyA art-NO aspect-NA case-NOCASE clitic-NO conj-NO def-DEF mood-NA n

um-SG part-NO per-3 pos-PN voice-NA*0.78571


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– Derivational Morphology

– Inflectional Morphology – Morphological Ambiguity – Arabic Computational Morphology

• Syntax


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Arabic Computational Morphology• Representation units• Natural token ت ـ ـ ـ ـ ـ ـ ـ ـ و

– White space separated strings (as is) – Can include extra characters (e.g. tatweel/kashida)

•Word وت

• Segmented word – Can include any degree of morphological analysis – Pure segmentation:

ت

ل

و

– Arabic Treebank tokens (with recovery of somedeleted/modified letters):

ت

ل

و


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Arabic Computational Morphology• Representation units (continued)• Prefix + Stem + Suffix

–و++

– Can create more ambiguity• Lexeme + Features

– [+Plural +Def + +ل ]

• Root + Pattern + Features –

آ

+ة

a3a21aم

+ [+Plural +Def +ل

+و

] – Very abstract

• Root + Pattern + Vocalism + Features – آ + 321م + a.a.a + [+Plural +Def +ل [و+ – Very very abstract

(Habash&Sadat 2006)


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TOKAN• A generalized tokenizer • Assumes disambiguated morphological analysis

– a la MADA

• Declarative specification of tokenization scheme wsyktbhA=[katab_1 POS:V +IV w+ s+ +S:3MS +O:3FS]

• Uses generator (Habash 2004)

w+ f+ b+ k+ l+ s+ Al+ LEXEME + BIESPOS +S:ENw+ s+ ktb/VBZS:3MS +hA

w+ f+ b+ k+ l+ REST +P: +O:TBw+ syktb +hA

w+ f+ b+ k+ l+ s+ Al+ REST +P: +O:D3w+ s+ yktb +hA

w+ f+ b+ k+ l+ s+ RESTD2w+ s+ yktbhA

w+ f+ RESTD1w+ syktbhA

SpecificationSchemeExample


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Arabic Computational Morphology• Approaches – Finite state machines (Beesely,2001) (Kiraz,2001) (Habash&Rambow 2006) – Concatenative analysis/generation (Smrz, 2007) (Buckwlater,2002)

(Cavalli-Sforza et al, 2000)

– Lexeme+Feature analysis/generation (Habash, 2004) (Habash&Rambow2006)

– Shallow stemming (Darwish,2002) (Aljlayl and Frieder 2002) – Machine learning (Diab et al,2004) (Lee et al,2003) (Rogati et al, 2003)

(Habash & Rambow 2005a)

– Survey article: (Al-Sughaiyer&Al-Kharashi, 2004)• Issues

– Appropriateness of system representation for an application• Machine Translation vs. Information Retrieval

• Arabic spelling vs. phonetic spelling – System coverage – System extendibility – Availability to researchers – Use for analysis and generation


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• Syntax – Morphology and Syntax

– Sentence Structure – Phrase Structure

– Computational Resources


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Morphology and Syntax• Rich morphology crosses into syntax

– Pro-drop / Subject conjugation

– Verb sub-categorization and object clitics• Verbtransitive+subject+object• Verbintransitive+subject but not Verbintransitive+subject+object• Verbpassive+subject but not Verbpassive+subject+object

• Morphological interactions with syntax – Agreement• Full: e.g. Noun-Adjective on number, gender, and definiteness (for

persons)• Partial: e.g. Verb-Subject on gender (in VSO order)

– Definiteness• Noun compound formation, copular sentences, etc.• Nouns+DefiniteArticle, Proper Nouns, Pronouns, etc.


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Morphology and Syntax• Morphological interactions with syntax (continued)

– Case

• MSA is case marking: nominative, accusative, genitive• Almost-free word order • Case is often marked with optionally written short vowels

– This effectively limits the word-order freedom in published text

• Agglutination – Attached prepositions create words that cross phraseboundaries

ل

+ت

li+Almaktabātfor the-libraries [PP li [NP Almaktabāt]]

• Some morphological analysis (minimally segmentation)is necessary even for statistical approaches to parsing


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Sentence StructureTwo types of Arabic Sentences

• Verbal sentences – [Verb Subject Object] (VSO) – آا دوا

Wrote the-boys the-poems

The boys wrote the poems• Copular sentences (aka nominal sentences)

– [Topic Complement]

– د

و

اا

the-boys poetsThe boys are poets


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Sentence Structure• Verbal sentences

– Verb agreement with gender only• Default singular number • ا آ\وا wrote3MascSing the-boy/the-boys

• آا \ا wrote3FemSing the-girl/the-girls

– Pronominal subjects are conjugated• آ wrote-youMascSing• آ wrote-youMascPlur • آ wrote-theyMascPlur

– Passive verbs• Same structure: Verbpassive SubjectunderlyingObject• Agreement with surface subject


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Sentence Structure• Verbal sentences

– Common structural ambiguity• Third masculine/feminine singular

is structurally

ambiguous

– Verb3MascSingular NounMascVerb subject=he object=Noun

Verb subject=Noun

• Passive and active forms are often similar in

standard orthography – آ /kataba/ he wrote – آ /kutiba/ it was written


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Sentence Structure• Copular sentences

– [Topic Complement]

Definite Topic, Indefinite Complement• ا

the-boy poetThe boy is a poet

– [Auxiliary Topic Complement]Auxiliaries (kāna and her sisters)• Tense, Negation, Transformation, Persistence• ا آن was the-boy poet The boy was a poet • ا is-not the-boy poet The boy is not a poet

– Inverted order is expected in certain cases• Indefinite topic آ ي /ʕindi kitābun/ at-me a-book I have a book


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Sentence Structure• Copular sentences – Types of complements

• Noun/Adjective/Adverb – اآذ the-boy smart The boy is smart

• Prepositional Phrase – ا ا the-boy in the-library The boy is in the library

• Copular-Sentence – اآ آ [the-boy [book-his big]] The boy, his book is big

• Verb-Sentence – اآ اود

[the-boys [wrote3rdMascPlur poems]] The boys wrote the poems

– Full agreement in this order (SVO)

– اوآ ار

[the-poems [wrote3rdMascSing-them the boys]] The poems, the boys wrote


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Phrase Structure• Noun Phrase

– Determiner Noun Adjective PostModifier

• ان this the-writer the-ambitious the-arriving from Japanها ا اح ادمThis ambitious writer from Japan

– Noun-Adjective agreement• number, gender, definiteness

– ا ا the-writer FemSing the-ambitiousFemSing – ا ا the-writer FemPlur the-ambitiousFemPlur

• Exception: Plural non-persons – definiteness agreement; feminine singular default – ا ا the-officeMascSing the-newMascSing – ا ا the-libraryFemSing the-newFemSing – ا ا the-officesMascBPlur the-newFemSing – ا ا the-librariesFemPlur the-newFemSing


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Phrase Structure• Noun Phrase

– Idafa construction (ا)

• Noun1 of Noun2 encoded structurally• Noun1-indefinite Noun2-definite اردن •

king Jordanthe king of Jordan / Jordan’s king

– Noun1 becomes definite• Agrees with definite adjectives

– Idafa chains• N 1

indef

N 2 indef

… N n-1indef

N ndef • آا ةرادا ر ر ا

son uncle neighbor chief committee management the-companyThe cousin of the CEO’s neighbor


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Phrase Structure• Morphological definiteness interacts with syntactic structure

Indefinitedefinite

Noun Phrase

آAn artist(ic) writer

Copular Sentence

اThe writer is an artist

Noun Compound

آاThe writer of the artist

Noun Phrase

ا اThe artist(ic) writer

Word 1 آ writer

W o r

d 2

a r t i s t

d e f i n i t e

i n d e f i n i t e

Agreement in Arabic


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g• Verb-Subject agreement

– Verb agrees with subject in full (gender,number)• Exception: partial agreement (number=singular) in VSO order • Exception: partial agreement (number=singular; gender=feminine) for non-person plural

subjects regardless of order • Noun-Adjective

– Adjective agrees with noun in full (gender, number, definiteness and case)• Exception: partial agreement (number=singular; gender=feminine) for non-person plural

nouns

• Noun-Number

– Number is the syntactic-case head – for numbers [3..10]: Noun is plural+genitive (idafa); number gender is inverted gender

of noun! – for numbers [11..99]: Noun is singular+accusative (tamyiyz/specification); number

gender is even more complicated☺ – for numbers [100,1K,1M]: Noun is singular+genitive (idafa)

Adjectives of plural non-person nouns are Fem+Sg

Numbers agrees bygender inversion

Verbs in VSO order are alwaysSg and agree in gender only

Fem+Sg+GenFem+PL+GenMasc+Sg+NomFem+Sg

jdydp ‘new’ jAmEAt ‘universities’ vlAv ‘three’ bnyt ‘was built’


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Computational Resources• Monolingual corpora for building language models

– Arabic Gigaword

• Agence France Presse• AlHayat News Agency• AnNahar News Agency• Xinhua News Agency

– Arabic Newswire – United Nations Corpus (parallel with other UN languages) – Ummah Corpus (parallel with English)

• Distributors – Linguistic Data Consortium (LDC) – Evaluations and Language resources Distribution Agency

(ELDA)

Computational Resources


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p

• Penn Arabic Treebank (PATB) – Started in 2001

– Goal is 1 Million words – Currently 650K words

• Agence France Presse , AlHayat newspaper, AnNahar newspaper

• POS tags – Buckwalter analyzer – Arabic-tailored POS list

• PATB constituencyrepresentation – Some modifications of Penn English Treebank

• (e.g. Verb-phrase internal subjects)



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p

• Prague Dependency Treebank

• Partial overlap with PATBand Arabic Gigaword – Agence France Presse,

AlHayat and Xinhua• Morphological analysis

– Extends on PATB

• Dependency representation

Graphic courtesy of Otakar Smrž: http://ckl.mff.cuni.cz/padt/PADT_1.0/docs/slides/2003-eacl-trees.ppt

CATiB:Columbia Arabic Tree Bank(Habash, 2009)


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• CATiB Representation – Lite Dependency Syntax

– Tokenization• CONJ PART BASE PRON – Part of Speech Tag set

• Six tags: VRB, VRB-pass, NOM,PROP, PRT, PNX

– Syntactic Annotation• Eight dependency relations: SBJ,

OBJ, TPC, PRD, IDF, TMZ, MOD, FLAT

• Practical Considerations

– Less information to annotate – Dependencies easier to annotate than phrase structure – Terminology and representation close to traditional

Arabic grammar



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• Applications using Arabic treebanks – Statistical parsing

• Bikel’s parser (Bikel 2003)

– Same engine used with English, Chinese and Arabic• Nivre’s MALT parser (Nivre et al. 2006) – Base-phrase Chunking

• (Diab et al, 2004; Diab et al. 2007) – POS tagging and morphological disambiguation

• (Diab et al, 2004; Diab et al. 2007; Habash and Rambow, 2005a; Smith etal., 2005; Roth et al. 2008)

• Other non-treebank-based POS tagging efforts: (Khoja, 2001)

• Formalism conversion – Constituency to dependency (Žabokrtský and Smrž 2003; Habash et al.

2007; Tounsi et al., 2009)

– Tree-adjoining grammar extraction (Habash and Rambow 2004)• Automatic diacritization

– Zitouni et al. (2006); Habash&Rambow (2007); Shaalan et al (2008)among others

– Diacritization for MT (Diab et al. 2007)

Other Tutorial Slides


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• Columbia’s Arabic Dialect

Modeling Group (CADIM) – http://www1.ccls.columbia.edu/~cadim/

• Presentations

MEADR 2009Cairo, Egypt

A il 21 2009


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Introduction to ArabicNatural Language Processing

Nizar HabashColumbia University

Center for Computational Learning Systems

[email protected]

April 21, 2009

CADIM

Introduction to Arabic NLP

Documents

Transcript of Introduction to Arabic NLP