Paradigm based Morphological Analyzers

Dr. Radhika Mamidi

Morphological Analyzers

They are tools to automatically decompose a word into its root and affixes and give related features.

Example:1st stage – identifying morphemes

ate: root = eat

suffix = ed

2nd stage – analyzing morphemes

ate: root = eat

tense = past

Some Applications

• Machine Translation

• Speech Processing

Machine Translation

• Pos tagger gives only part of speech. More information is needed to translate a word correctly.

• More information like tense, aspect and mood of the verbs, gender, number and person of the nouns.

Example: [Eng Hindi translation]

ENGLISH: She went home.HINDI: vaha ghar gayi.

ENGLISH: He went home.HINDI: vaha ghar gayaa.

• The gender of the pronoun is essential for the translation in Hindi.

• The morph analyzer will give the gender information.

Example: [Hindi Eng translation]

In Hindi ‘vaha’ can have different senses – ‘he’, ‘she’ or ‘that’.

“vaha ghar gayaa”

If we were to translate this, then the extra information on the verb will help us to translate the above sentence correctly as

“He went home”

• The ‘yaa’ indicates past tense as well as singular number and masculine gender.

• The morph analyzer will give this information.

Speech Processing

• In Text to Speech tools also Morph Analyzer is essential along with Part of Speech.

• With extra information on the words, the efficiency increases.

• The intonation, the pause, the stress etc can be close to the way humans speak.

• This additional information is given by morph analyzers.

Approaches

• Paradigm based

• Finite State based

We will discuss the first approach.

Requirement for building paradigm based Morph Analyzers

• Knowledge of Lexeme and Word forms

• Root and Affix dictionaries

• Paradigm Table

• Paradigm class

• The lexemes are stored in the dictionaries and the word forms as paradigms.

Lexeme and Word form

APPLE: apple, applesCHURCH: church, churchesBOY: boy, boysWATCH: watch, watches

SPY: spy, spies

• The word in upper case is called LEXEME and the inflected forms are WORD FORMS.

• Lexemes are the headwords in a dictionary.

Lexeme and Word form

Another example:

played is a word form of the lexeme PLAYplays is a word form of the lexeme PLAY(1)plays is a word form of the lexeme PLAY(2)

where PLAY(1) is a verb and PLAY(2) is a noun.

PLAY(1) and PLAY(2) are two different lexemes.

Exercise 1

Give the lexeme of the following word forms ate played manufactured glasses players bites

Exercise 2“manufactured” can be a verb in past tense or an

adjective. So it belongs to two different lexemes – manufacture and manufactured.

Which of the following words belong to more than one lexeme?

atewantedwrotewrittenfinished

Root and Affix dictionaries

Root dictionary contains a list of roots or the base forms to which affixation takes place.

It is stored usually with its part of speech.

Affix dictionary contains a list of all the affixes in a language.

The features of the affixes are stored here.The features are stored as attribute value

pairs.

Example entries in a dictionary

Root dictionaryeat <root=‘eat’, category=‘verb’>book <root=‘book’, category=‘verb’>book <root=‘book’, category=‘noun’>

Affix dictionary+s <tense = ‘present’>+ed <tense = ‘past’>+en <aspect = ‘perfective’>+ing <aspect = ‘progressive’>

Paradigm table

A paradigm table represents the inflected forms of a particular word.

It includes the conjugation of verbs and declensions of nouns, adjectives, pronouns etc.

Example:

apple, apples

eat, eats, ate, eaten, eating

smart, smarter, smartest

Conjugation of English verbs

• play plays played played playing

• eat eats ate eaten eating

• look looks looked looked looking

• dance dances danced danced dancing

• push pushes pushed pushed pushing

Declension of English nouns

• apple, apples

• boy, boys

• church, churches

• watch, watches

• spy, spies

Exercise 3

• Give the paradigm table for 5 different nouns and 5 different verbs in English.

Paradigm Class

• A paradigm class contains the classes of words i.e. the prototypical root and all the roots that fall in its class including the given root.

• By the term ‘root’ we mean the base form or stem to which affixation takes place.

• Those words which decline or conjugate in exactly the same way, fall into one class.

The English verbs ‘play’ and ‘look’ have the following paradigm:

• play plays played played playing• look looks looked looked lookingSo they belong to the same class.

But ‘push’ since it differs in its present tense form i.e. it has ‘-es’ and not ‘- s’ falls in another class. Its paradigm is as follows:

• push pushes pushed pushed pushing

The English nouns ‘play’ and ‘boy’ have the following paradigm:

• play plays

• boy boys

So they belong to the same class.

But ‘spies’ falls in another class. Its paradigm is as follows:

• spy spies

Paradigm class is represented by one member of the class.

eat V eat

play V play, talk, walk, train

push V push, fish

play N play, boy, day

spy N spy, sky

church N church, watch

Exercise 4Which of the following verbs belong to the same

paradigm class?mince ride walk speakshake play dance take

Which of the following nouns belong to the same paradigm class?

girl house dish book mouse beach flower pencil