A Trie-Structured Bayesian Model for Unsupervised Morphological Segmentation

In this paper, we introduce a trie-structured Bayesian model for unsupervised morphological segmentation. We adopt prior information from different sources in the model. We use neural word embeddings to discover words that are morphologically derived from each other and thereby that are semantically similar. We use letter successor variety counts obtained from tries that are built by neural word embeddings. Our results show that using different information sources such as neural word embeddings and letter successor variety as prior information improves morphological segmentation in a Bayesian model. Our model outperforms other unsupervised morphological segmentation models on Turkish and gives promising results on English and German for scarce resources.Comment: 12 pages, accepted and presented at the CICLING 2017 - 18th International Conference on Intelligent Text Processing and Computational Linguistic

U.S. Foreign Direct Investment and Host Country Labour Market Competitiveness

This paper’s primary goal is to investigate whether host country labour market competitiveness and labour standards affect the location decision of U.S. firms. The analysis is based on a regression model using time series data on FDI, skills, host country’s GDP, the corporate income tax rate, distance, and other variables. We also use cooperation between labour and employers as a measure of labour standards. Considerable support is found for the importance of labour standards in affecting the location decision U.S. firms

Unsupervised learning of allomorphs in Turkish

© 2017 The Author. Published by The Scientific and Technological Research Council of Turkey. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://journals.tubitak.gov.tr/elektrik/issues/elk-17-25-4/elk-25-4-57-1605-216.pdfOne morpheme may have several surface forms that correspond to allomorphs. In English, ed and d are surface forms of the past tense morpheme, and s, es, and ies are surface forms of the plural or present tense morpheme. Turkish has a large number of allomorphs due to its morphophonemic processes. One morpheme can have tens of different surface forms in Turkish. This leads to a sparsity problem in natural language processing tasks in Turkish. Detection of allomorphs has not been studied much because of its difficulty. For example, t¨u and di are Turkish allomorphs (i.e. past tense morpheme), but all of their letters are different. This paper presents an unsupervised model to extract the allomorphs in Turkish. We are able to obtain an F-measure of 73.71% in the detection of allomorphs, and our model outperforms previous unsupervised models on morpheme clustering.Published versio

Incorporating word embeddings in unsupervised morphological segmentation

We investigate the usage of semantic information for morphological segmentation since words that are derived from each other will remain semantically related. We use mathematical models such as maximum likelihood estimate (MLE) and maximum a posteriori estimate (MAP) by incorporating semantic information obtained from dense word vector representations. Our approach does not require any annotated data which make it fully unsupervised and require only a small amount of raw data together with pretrained word embeddings for training purposes. The results show that using dense vector representations helps in morphological segmentation especially for low-resource languages. We present results for Turkish, English, and German. Our semantic MLE model outperforms other unsupervised models for Turkish language. Our proposed models could be also used for any other low-resource language with concatenative morphology.</p

Turkish lexicon expansion by using finite state automata

© 2019 The Authors. Published by The Scientific and Technological Research Council of Turkey. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://journals.tubitak.gov.tr/elektrik/issues/elk-19-27-2/elk-27-2-25-1804-10.pdfTurkish is an agglutinative language with rich morphology. A Turkish verb can have thousands of different word forms. Therefore, sparsity becomes an issue in many Turkish natural language processing (NLP) applications. This article presents a model for Turkish lexicon expansion. We aimed to expand the lexicon by using a morphological segmentation system by reversing the segmentation task into a generation task. Our model uses finite-state automata (FSA) to incorporate orthographic features and morphotactic rules. We extracted orthographic features by capturing phonological operations that are applied to words whenever a suffix is added. Each FSA state corresponds to either a stem or a suffix category. Stems are clustered based on their parts-of-speech (i.e. noun, verb, or adjective) and suffixes are clustered based on their allomorphic features. We generated approximately 1 million word forms by using only a few thousand Turkish stems with an accuracy of 82.36%, which will help to reduce the out-of-vocabulary size in other NLP applications. Although our experiments are performed on Turkish language, the same model is also applicable to other agglutinative languages such as Hungarian and Finnish.Published versio

Unsupervised morphological segmentation using neural word embeddings

This is an accepted manuscript of an article published by Springer in Král P., Martín-Vide C. (eds) Statistical Language and Speech Processing. SLSP 2016. Lecture Notes in Computer Science, vol 9918 on 21/09/2016, available online: https://doi.org/10.1007/978-3-319-45925-7_4 The accepted version of the publication may differ from the final published version.We present a fully unsupervised method for morphological segmentation. Unlike many morphological segmentation systems, our method is based on semantic features rather than orthographic features. In order to capture word meanings, word embeddings are obtained from a two-level neural network [11]. We compute the semantic similarity between words using the neural word embeddings, which forms our baseline segmentation model. We model morphotactics with a bigram language model based on maximum likelihood estimates by using the initial segmentations from the baseline. Results show that using semantic features helps to improve morphological segmentation especially in agglutinating languages like Turkish. Our method shows competitive performance compared to other unsupervised morphological segmentation systems.Published versio

Transfer learning for Turkish named entity recognition on noisy text

This is an accepted manuscript of an article published by Cambridge University Press in Natural Language Engineering on 28/01/2020, available online: https://doi.org/10.1017/S1351324919000627 The accepted version of the publication may differ from the final published version.© Cambridge University Press 2020. In this article, we investigate using deep neural networks with different word representation techniques for named entity recognition (NER) on Turkish noisy text. We argue that valuable latent features for NER can, in fact, be learned without using any hand-crafted features and/or domain-specific resources such as gazetteers and lexicons. In this regard, we utilize character-level, character n-gram-level, morpheme-level, and orthographic character-level word representations. Since noisy data with NER annotation are scarce for Turkish, we introduce a transfer learning model in order to learn infrequent entity types as an extension to the Bi-LSTM-CRF architecture by incorporating an additional conditional random field (CRF) layer that is trained on a larger (but formal) text and a noisy text simultaneously. This allows us to learn from both formal and informal/noisy text, thus improving the performance of our model further for rarely seen entity types. We experimented on Turkish as a morphologically rich language and English as a relatively morphologically poor language. We obtained an entity-level F1 score of 67.39% on Turkish noisy data and 45.30% on English noisy data, which outperforms the current state-of-art models on noisy text. The English scores are lower compared to Turkish scores because of the intense sparsity in the data introduced by the user writing styles. The results prove that using subword information significantly contributes to learning latent features for morphologically rich languages.Published versio

Stemming Turkish Words with LSTM Networks

© 2019 Journal of Information Technologies (BTD). For re-use please contact the publisher.Türkçe, morfem adı verilen birimlerin art arda eklenmesiyle sözcüklerin oluşturulduğu sondan eklemeli bir dildir. Sözcüklerin farklı parçaların birleştirilmesiyle oluşturulması makine tercümesi, duygu analizi ve bilgi çıkarımı gibi birçok doğal dil işleme uygulamasında seyreklik problemine yol açmaktadır çünkü sözcüğün her farklı formu farklı bir sözcük gibi algılanmaktadır. Bu makalede, sözcüklerin yapım ve çekim eklerinden arındırılarak köklerinin otomatik olarak bulunabilmesi için bir yöntem öneriyoruz. Kullandığımız yöntem tekrarlayan sinir ağları kullanarak oluşturulan kodlayıcı-kod çözücü yaklaşımına dayanmaktadır. Verilen herhangi bir sözcük, oluşturduğumuz sinir ağı yapısı ile öncelikle kodlanmakta, ardından kodu çözülerek köküne ulaşılabilmektedir. Bu yöntem şimdiye kadar etiketleme veya makine tercümesi gibi problemlerde kullanılmıştır. Diğer Türkçe kök bulma modelleriyle karşılaştırıldığında sonuçların oldukça iyi olduğu gözlenmiştir. Diğer modellerde olduğu gibi, herhangi bir kural kümesi elle tanımlanmadan, sadece sözcük ve kök ikililerinden oluşan bir eğitim veri kümesi kullanılarak kök bulma işlemi önerdiğimiz bu model ile gerçekleştirilebilmektedir.Published onlin