CSA4050: Advanced Topics in NLP Example Based MT

Man does translation, first, by properly decomposing an input sentence into certain fragmental phrases, then by translating these phrases into other language phrases, and finally by properly composing these fragmental translations into one long sentence. Nagao, 1984

Example Problem: translate He buys a book on international politics Database: He buys a notebook Kare wa noto o kau he topic notebook object buys I read a book on international politics Watachi wa kokusai seiji nitsuite kakareta hon o yomu Answer: kare wa kokusai seiji nitsuite kakareta hon o kau.

Translation Process Input: he buys a book on international politics Indentify/translate fragments –he buys kare wa ….. kau –a book on international politics kokusai seiji nitsuite kakareta hon Combine translated fragments. kare wa kokusai seiji nitsuite kakareta hon kau

Three Step Process Match: identify relevant source language examples in database. Align: find corresponding fragments in target language. Recombine: target language fragments to form sentences.

Matching Nature of matching process depends on database organisation. In the simplest case it is simply a bilingual corpus that has been aligned at sentence level. Effectively this means that the database is a collection of sentence pairs. Identification of relevant pairs is carried out by matching sentences.

Matching Different methods of sentence/sentence matching Character Based Word Based Structure Based Partial

Character Based Problem – semantic edit distance versus character edit distance Paper tray A holds up to 400 sheets Paper tray B holds up to 400 sheets The large paper tray The small paper tray d=1 d=5

Word Based Allows matching between different words on the basis of a similarity metric (e.g based on semantic features). This allows inexact matches and also solves the problem of which stored translation to choose. In the following case which involve different translations for the word “eat” in Japanese. Stored: A man eats vegetables. Acid eats metal. Example to translate: He eats potatoes

Matching Fragments He buys a book on international politics he buys a notebook he buys a horse he buys a car for his mum he buys a politician John buys toothpaste he reads a book on international politics books on international poltics are exciting John sold a a book on antiques

Bibliography Example Based MT H Somers – Review Article Machine Translation 14.2