approaches is not very straightforward. One categorization possible is based on information sources used in the process. The categorization is as follows:
1.1.1 Grapheme Based Models
Grapheme based transliteration is a process of mapping a grapheme sequence from a source language to a target language. In this approach characters from source language are directly mapped to characters of target language. So, they are also called direct methods. This approach mainly relies upon statistical information that can be obtained from characters. Grapheme based models are classified into the Statistical Machine Transliteration (SMT) based model, Rule based models, Hidden Markov Model , Finite State Transducer (FST) based model.
1.1.2 Phoneme Based Model
Phonemes are the smallest significant units of sound. In phoneme based approach, the written word of source language is mapped to written word of target language via the spoken form associated with the word. Phoneme based method is also known as Pivot method 1. The reason for using this approach is that phonetical representation makes it possible to use it as an intermediate form between source and target languages (Similar to interlingua MT). The other reason for the interest in phonetic based transliteration is its ability to capture the pronunciation of the words. This model therefore usually needs two steps: 1) produce source language phonemes from source language graphemes and 2) produce target language graphemes from source phonemes. Phonetic-based methods identify phonemes in the source word W, produce source language phonemes (P) and then map the phonetical representation of those phonemes (P) to character representations in the target language to generate the target word(s) T.
In phoneme based approaches, the transliteration key is the pronunciation of the source phoneme rather than spelling or the source grapheme. The phoneme based approach has also received remarkable attention in various works. Based on phonology, the source text can be transliterated to target text in terms of pronunciation similarities between them. The syllables are mapped to phonemes, based on some transcription rules 1. The mapping templates between phonemes of source and target language are the transliteration rules.