Expanding Parallel Resources for Medium-Density Languages for Free
Georgi Iliev, Angel Genov · 2012
We discuss a previously proposed method for augmenting parallel corpora of limited size for the purposes of machine translation through monolingual paraphrasing of the source language.We develop a three-stage shallow paraphrasing procedure to be applied to the Swedish-Bulgarian language pair for which limited parallel resources exist.The source language exhibits specifics not typical of high-density languages already studied in a similar setting.Paraphrases of a highly productive type of compound nouns in Swedish are generated by a corpus-based technique.Certain Swedish noun-phrase types are paraphrased using basic heuristics.Further we introduce noun-phrase morphological variations for better wordform coverage.We evaluate the performance of a phrase-based statistical machine translation system trained on a baseline parallel corpus and on three stages of artificial enlargement of the source-language training data.Paraphrasing is shown to have no effect on performance for the Swedish-English translation task.We show a small, yet consistent, increase in the BLEU score of Swedish-Bulgarian translations of larger token spans on the first enlargement stage.A small improvement in the overall BLEU score of Swedish-Bulgarian translation is achieved on the second enlargement stage.We find that both improvements justify further research into the method for the Swedish-Bulgarian translation task.