Word.alignment: an R package for computing statistical word alignment and its evaluation

Abstract

Word alignment has lots of applications in various natural language processing (NLP) tasks. As far as we are aware, there is no word alignment package in the R environment. In this paper, word.alignment, a new R software package is introduced which implements a statistical word alignment model as an unsupervised learning. It uses IBM Model 1 as a machine translation model based on the use of the EM algorithm and the Viterbi search in order to find the best alignment. It also provides the symmetric alignment using three heuristic methods such as union, intersection, and grow-diag. It has also the ability to build an automatic bilingual dictionary applying an innovative rule. The generated dictionary is suitable for a number of NLP tasks. This package provides functions for measuring the quality of the word alignment via comparing the alignment with a gold standard alignment based on five metrics as well. It is easily installed and executable on the mostly widely used platforms. Note that it is easily usable and we show that its results are almost everywhere better than some other word alignment tools. Finally, some examples illustrating the use of word.alignment is provided.