Does normalization help Part-of-Speech (POS) tagging accuracy on noisy, non-canonical data? To the best of our knowledge, little is known on the actual impact of normalization in a real-world scenario, where gold error detection is not available. We investigate the effect of automatic normalization on POS tagging of tweets. We also compare normalization to strategies that leverage large amounts of unlabeled data kept in its raw form. Our results show that normalization helps, but does not add consistently beyond just word embedding layer initialization. The latter approach yields a tagging model that is competitive with a Twitter state-of-the-art tagger.
Finally, normalization for POS tagging is certainly not limited to non-canonical data stemming from social media. Indeed, another stream of related work is focused on historical data, usually originating from the 15th till the 18th century. The motivation behind this is that in order to apply current language processing tools, the texts need to be normalized first, as spelling has changed through time. Experiments on POS tagging historical data that was previously normalized have been investigated for English @cite_3 , German @cite_4 , and Dutch . In this latter work, different methods of translating' historical Dutch texts to modern Dutch are explored, and a vocabulary lookup-based approach appears to work best. Interestingly, this work also resulted in a shared task on normalization of historical Dutch, in which the secondary evaluation metric was POS tagging accuracy: https: ifarm.nl clin2017st . In this paper we focused on normalization and POS tagging for Twitter data only.
@cite_4 @cite_3
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This paper presents a method for part-ofspeech tagging of historical data and evaluates it on texts from different corpora of historical German (15th–18th century). Spelling normalization is used to preprocess the texts before applying a POS tagger trained on modern German corpora. Using only 250 manually normalized tokens as training data, the tagging accuracy of a manuscript from the 15th century can be raised from 28.65 to 74.89 . Despite significant recent work, purely unsupervised techniques for part-of-speech (POS) tagging have not achieved useful accuracies required by many language processing tasks. Use of parallel text between resource-rich and resource-poor languages is one source of weak supervision that significantly improves accuracy. However, parallel text is not always available and techniques for using it require multiple complex algorithmic steps. In this paper we show that we can build POS-taggers exceeding state-of-the-art bilingual methods by using simple hidden Markov models and a freely available and naturally growing resource, the Wiktionary. Across eight languages for which we have labeled data to evaluate results, we achieve accuracy that significantly exceeds best unsupervised and parallel text methods. We achieve highest accuracy reported for several languages and show that our approach yields better out-of-domain taggers than those trained using fully supervised Penn Treebank. For Chinese POS tagging, word segmentation is a preliminary step. To avoid error propagation and improve segmentation by utilizing POS information, segmentation and tagging can be performed simultaneously. A challenge for this joint approach is the large combined search space, which makes efficient decoding very hard. Recent research has explored the integration of segmentation and POS tagging, by decoding under restricted versions of the full combined search space. In this paper, we propose a joint segmentation and POS tagging model that does not impose any hard constraints on the interaction between word and POS information. Fast decoding is achieved by using a novel multiple-beam search algorithm. The system uses a discriminative statistical model, trained using the generalized perceptron algorithm. The joint model gives an error reduction in segmentation accuracy of 14.6 and an error reduction in tagging accuracy of 12.2 , compared to the traditional pipeline approach. In this paper, a method based on part-of-speech tagging (PoS) is used for bibliographic reference structure. This method operates on a roughly structured ASCII file, produced by OCR. Because of the heterogeneity of the reference structure, the method acts in a bottom-up way, without an a priori model, gathering structural elements from basic tags to sub-fields and fields. Significant tags are first grouped in homogeneous classes according to their grammar categories and then reduced in canonical forms corresponding to record fields: "authors", "title", "conference name", "date", etc. Non labelled tokens are integrated in one or another field by either applying PoS correction rules or using a structure model generated from well-detected records. The designed prototype operates with a great satisfaction on different record layouts and character recognition qualities. Without manual intervention, 96.6 words are correctly attributed, and about 75.9 references are completely segmented from 2500 references.