Context-based Translation for the Out of Vocabulary Words Applied to Hindi-English Cross-Lingual Information Retrieval

Abstract

Cross-Lingual Information Retrieval (CLIR) provides flexibility to users to query in their regional (source) languages regardless the target documents languages. CLIR uses trending translation techniques Statistical Machine Translation (SMT) and Neural Machine Translation (NMT). SMT and NMT achieve good results for foreign languages but not for Indian languages due to non-absoluteness of the parallel corpus. Source language user queries may contain the Out Of Vocabulary (OOV) words which are not present in the parallel corpus such words may be skipped without performing translation by SMT. In this paper, a context-based translation algorithm is proposed to translate the OOV words by utilizing two unlabeled & unrelated large raw corpora (in source and target language) and a small bi-lingual parallel corpus. Since SMT performs better than NMT for Hindi to English translation as per the literature, therefore, experimental results are evaluated for FIRE datasets against baseline SMT. The proposed algorithm improves evaluation measures, Recall up to 6.04% (0.8785) for FIRE 2010 and up to 3.96% (0.7365) for FIRE 2011, & Mean Average Precision (MAP) up to 14.37% (0.3239) for FIRE 2010 and up to 5.46% (0.1988) for FIRE 2011, in comparison to the baseline SMT which achieves 0.8284 and 0.7084 Recall for FIRE 2010 and 2011, & 0.2832 and 0.1885 MAP for FIRE 2010 and 2011. An analysis for the number of OOV words shows that the proposed algorithm reduces the number of OOV more effectively, up to 0.81% for FIRE 2010 and 1.73% for FIRE 2011.