This paper investigates the robustness of NLP against perturbed word forms. While neural approaches can achieve (almost) human-like accuracy for certain tasks and conditions, they often are sensitive to small changes in the input such as non-canonical input (e.g., typos). Yet both stability and robustness are desired properties in applications involving user-generated content, and the more as humans easily cope with such noisy or adversary conditions. In this paper, we study the impact of noisy input. We consider different noise distributions (one type of noise, combination of noise types) and mismatched noise distributions for training and testing. Moreover, we empirically evaluate the robustness of different models (convolutional neural networks, recurrent neural networks, non-neural models), different basic units (characters, byte pair encoding units), and different NLP tasks (morphological tagging, machine translation).
The arbitrary relationship between the orthography of a word and its meaning in general is a well known assumption in linguistics @cite_6 . However, the word form often carries additional important information. This is, for example, the case in morphologically rich languages or in non-normalized text where small perturbations result in similar word forms. Recently, sub-word units have attracted some attention in NLP to handle rarely and unseen words and to reduce the computational complexity in neural network approaches @cite_28 @cite_8 @cite_13 @cite_15 @cite_3 . Examples for sub-word units include BPE based units @cite_13 , characters @cite_28 @cite_15 @cite_3 or even bytes @cite_8 . A comparison of BPE and characters for machine translation regarding grammaticality can be found in @cite_0 .
@cite_8 @cite_28 @cite_6 @cite_3 @cite_0 @cite_15 @cite_13
2106512229 2128810992 2251804196 1626233182
We propose the use of the word categories and embeddings induced from raw text as auxiliary features in dependency parsing. To induce word features, we make use of contextual, morphologic and orthographic properties of the words. To exploit the contextual information, we make use of substitute words, the most likely substitutes for target words, generated by using a statistical language model. We generate morphologic and orthographic properties of word types in an unsupervised manner. We use a co-occurrence model with these properties to embed words onto a 25dimensional unit sphere. The AI-KU system shows improvements for some of the languages it is trained on for the first Shared Task of Statistical Parsing of Morphologically Rich Languages. Given a parallel corpus, if two distinct words in language A, a1 and a2, are aligned to the same word b1 in language B, then this might signal that b1 is polysemous, or it might signal a1 and a2 are synonyms. Both assumptions with successful work have been put forward in the literature. We investigate these assumptions, along with other questions of word sense, by looking at sampled parallel sentences containing tokens of the same type in English, asking how often they mean the same thing when they are: 1. aligned to the same foreign type; and 2. aligned to different foreign types. Results for French-English and Chinese-English parallel corpora show similar behavior: Synonymy is only very weakly the more prevalent scenario, where both cases regularly occur. We present a novel, count-based approach to obtaining inter-lingual word representations based on inverted indexing of Wikipedia. We present experiments applying these representations to 17 datasets in document classification, POS tagging, dependency parsing, and word alignment. Our approach has the advantage that it is simple, computationally efficient and almost parameter-free, and, more importantly, it enables multi-source crosslingual learning. In 14 17 cases, we improve over using state-of-the-art bilingual embeddings. We propose a novel context heterogeneity similarity measure between words and their translations in helping to compile bilingual lexicon entries from a non-parallel English-Chinese corpus. Current algorithms for bilingual lexicon compilation rely on occurrence frequencies, length or positional statistics derived from parallel texts. There is little correlation between such statistics of a word and its translation in non-parallel corpora. On the other hand, we suggest that words with productive context in one language translate to words with productive context in another language, and words with rigid context translate into words With rigid context. Context heterogeneity measures how productive the context of a word is in a given domain, independent of its absolute occurrence frequency in the text. Based on this information, we derive statistics of bilingual word pairs from a non-parallel corpus. These statistics can be used to bootstrap a bilingual dictionary compilation algorithm.