Chinese Named Entity Recognition Using Role Model

This paper presents a stochastic model to tackle the problem of Chinese named entity recognition. In this research, we unify component tokens of named entity and their contexts into a generalized role set, which is like part-of-speech (POS). The probabilities of role emission and transition are acquired after machine learning on a role-labeled data set, which is transformed from a hand-corrected corpus after word segmentation and POS tagging are performed. Given an original string, role Viterbi tagging is employed on tokens segmented in the initial process. Then named entities are identified and classified through maximum matching on the best role sequence. In addition, named entity recognition using role model is incorporated along with the unified class-based bigram model for word segmentation. Thus, named entity candidates can be further selected in the final process of Chinese lexical analysis. Various evaluations conducted using one month of news from the People's Daily and MET-2 data set demonstrate that the role modeled can achieve competitive performance in Chinese named entity recognition. We then survey the relationship between named entity recognition and Chinese lexical analysis via experiments on a 1,105,611-word corpus using comparative cases. It was found that: on one hand, Chinese named entity recognition substantially contributes to the performance of lexical analysis; on the other hand, the subsequent process of word segmentation greatly improves the precision of Chinese named entity recognition. We have applied the role model to named entity identification in our Chinese lexical analysis system, ICTCLAS, which is free software and available at the Open Platform of Chinese NLP (www.nlp.org.cn). ICTCLAS ranked first with 97.58% in word segmentation precision in a recent official evaluation, which was held by the National 973 Fundamental Research Program of China.