On top of the pruning framework, we also propose a discriminative ITG alignment model using hierarchical phrase pairs , which improves both F-score and Bleu score over the baseline alignment system of GIZA++.

On top of the discriminative pruning method, we also propose a discriminative ITG alignment system using hierarchical phrase pairs .

Another is DITG with hierarchical phrase pairs (henceforth HP-DITG), which relaxes the l-to-l constraint by adopting hierarchical phrase pairs in Chiang (2007).

6.2 DITG with Hierarchical Phrase Pairs

Wu (1997) proposes a bilingual segmentation grammar extending the terminal rules by including phrase pairs .

f len +elen Where #linksincon is the number of links which are inconsistent with the phrase pair according to some simpler alignment model (e.g.

3 An inconsistent link connects a word Within the phrase pair to some word outside the phrase pair .

We refer to singleton phrases as phrase pairs that occur only in one sentence.

For these sentences, the decoder needs the singleton phrase pairs to produce an alignment.

Standard leaving-one-out assigns a fixed probability 04 to singleton phrase pairs .

The phrase translation table, which contains the bilingual phrase pairs and the corresponding translation probabilities, is one of the main components of an SMT system.

The translation probability of a phrase pair (1216) is estimated as

where CFA(f, 6) is the count of the phrase pair (f, 6) in the phrase-aligned training data.

We will refer to this model as the count model as we simply count the number of occurrences of a phrase pair .

In the hierarchical phrase-based translation method, the translation rules are extracted by abstracting some words from an initial phrase pair (Chiang, 2005).

Consider a rule with non-terminals on the source and target side; for a given instance of the rule (a particular phrase pair in the training corpus), the context will be the words instantiating the non-terminals.

In turn, the context for the sub-phrases that instantiate the non-terminals will be the words in the remainder of the phrase pair .