A novel logographic subword model is proposed to reinterpret logograms as abstract subwords for neural machine translation. Our approach drastically reduces the size of an artificial neural network, while maintaining comparable BLEU scores as those attained with the baseline RNN and CNN seq2seq models. The smaller model size also leads to shorter training and inference time. Experiments demonstrate that in the tasks of English-Chinese Chinese-English translation, the reduction of those aspects can be from @math to as high as @math . Compared to previous subword models, abstract subwords can be applied to various logographic languages. Considering most of the logographic languages are ancient and very low resource languages, these advantages are very desirable for archaeological computational linguistic applications such as a resource-limited offline hand-held Demotic-English translator.
@cite_15: 
@cite_10: We present a new approach for neural machine translation (NMT) using the morphological and grammatical decomposition of the words (factors) in the output side of the neural network. This architecture addresses two main problems occurring in MT, namely dealing with a large target language vocabulary and the out of vocabulary (OOV) words. By the means of factors, we are able to handle larger vocabulary and reduce the training time (for systems with equivalent target language vocabulary size). In addition, we can produce new words that are not in the vocabulary. We use a morphological analyser to get a factored representation of each word (lemmas, Part of Speech tag, tense, person, gender and number). We have extended the NMT approach with attention mechanism in order to have two different outputs, one for the lemmas and the other for the rest of the factors. The final translation is built using some linguistic information. We compare our extension with a word-based NMT system. The experiments, performed on the IWSLT'15 dataset translating from English to French, show that while the performance do not always increase, the system can manage a much larger vocabulary and consistently reduce the OOV rate. We observe up to 2 BLEU point improvement in a simulated out of domain translation setup.
@cite_3: Neural machine translation (NMT) models typically operate with a fixed vocabulary, but translation is an open-vocabulary problem. Previous work addresses the translation of out-of-vocabulary words by backing off to a dictionary. In this paper, we introduce a simpler and more effective approach, making the NMT model capable of open-vocabulary translation by encoding rare and unknown words as sequences of subword units. This is based on the intuition that various word classes are translatable via smaller units than words, for instance names (via character copying or transliteration), compounds (via compositional translation), and cognates and loanwords (via phonological and morphological transformations). We discuss the suitability of different word segmentation techniques, including simple character n-gram models and a segmentation based on the byte pair encoding compression algorithm, and empirically show that subword models improve over a back-off dictionary baseline for the WMT 15 translation tasks English-German and English-Russian by 1.1 and 1.3 BLEU, respectively.
@cite_3 proposed to segment words of source and target sentences into smaller subword units using byte pair encoding (BPE) compression @cite_15 . They showed an improvement in the BLEU scores of 1.1 and 1.3 for English-German and English-Russian translations, respectively. Despite its advantage, BPE splits an alphabetic word to multiple letter groups, and thus it is intrinsically not applicable to logographic languages such as Chinese, Chorti, and Demotic (Ancient Egyptian) where a word is a glyph rather than alphabetic letters. Garc ' a-Mart ' @cite_10 proposed to decompose words morphologically and grammatically into factored representations such as lemmas, part-of-speech tag, tense, person, gender, and number. Their approach reduced training time and out of vocabulary (OOV) rates with improved translation performance, but also introduces unnecessary grammatical dependencies, (e.g. there are hundreds of tenseless languages), and is not optimized in all scenarios.