Paradigm based Morphological Analyzers

1. Paradigm based Morphological Analyzers Dr. Radhika Mamidi

2. 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

3. Some Applications • Machine Translation • Speech Processing

4. 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.

5. Example: [Eng Hindi translation] ENGLISH: Shewent home. HINDI: vaha ghar gayi. ENGLISH: Hewent 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.

6. 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.

7. 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.

8. Approaches • Paradigm based • Finite State based We will discuss the first approach.

9. 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.

10. Lexeme and Word form APPLE: apple, apples CHURCH: church, churches BOY: boy, boys WATCH: 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.

11. Lexeme and Word form Another example: played is a word form of the lexeme PLAY plays 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.

12. Exercise 1 Give the lexeme of the following word forms ate played manufactured glasses players bites

13. 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? ate wanted wrote written finished

14. 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.

15. Example entries in a dictionary Root dictionary eat <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’>

16. 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

17. 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

18. Declension of English nouns • apple, apples • boy, boys • church, churches • watch, watches • spy, spies

19. Exercise 3 • Give the paradigm table for 5 different nouns and 5 different verbs in English.

20. 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.

21. The English verbs ‘play’ and ‘look’ have the following paradigm: • play plays played played playing • look looks looked looked looking So 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

22. 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

23. 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

24. Exercise 4 Which of the following verbs belong to the same paradigm class? mince ride walk speak shake play dance take Which of the following nouns belong to the same paradigm class? girl house dish book mouse beach flower pencil