Part Of Speech Tagging and Chunking with HMM and CRF - LTRC

Table 8: Changes in POS tagging F-score beforeand after the application of transformation rulesPOS tag Before After DifferenceJJ 48.52 51.23 2.71JVB 43.94 45.31 1.37NLOC 71.43 72.92 1.49NN 72.43 76.35 3.92NNC 40.34 18.99 -21.35NNP 39.9 41.13 1.23NVB 37.56 42.49 4.93PREP 95.47 95.67 0.20QFN 89.42 90.48 1.06RP 89.63 89.93 0.30SYM 98.71 98.8 0.09VAUX 88.11 88.82 0.71VFM 80.96 82.67 1.71VJJ 16 10.53 -5.47John Lafferty, Andrew McCallum, and FernandoPereira. 2001. Conditional random fields: Probabilisticmodels for segmenting and labeling sequencedata. In Proceedings of the 18th InternationalConf. on Machine Learning, pages 282–289.Morgan Kaufmann, San Francisco, CA.L. R. Rabiner and B. H. Juang. 1986. An introductionto hidden markov models. IEEE ASSP Magazine,pages 4–16, January.Fei Sha and Fernando C. N. Pereira. 2003. Shallowparsing with conditional random fields. In Proceedingsof HLT-NAACL.measures of all tags except for NNC and VJJ. A reductionin the F-measure could have been avoidedby selecting a richer set of transformation templatesthan those listed in Table 1 as the transformationbased learning process is highly sensitiveto the templates used.In general the chunking accuracy for the combinedtask is lesser than the chunking task alonewith the reference tags. This is caused by thepropagation of errors introduced during the taggingprocess to the chunking stage.6 ConclusionWe have demonstrated the use of an off-the-shelfstatistical tagger combined with an error drivenlearning procedure for Part of Speech taggingHindi. The chunking task with Conditional RandomFields was also explored. We have reportedour results for each of these tasks separately andalso the results for the joint task of POS taggingand chunking.ReferencesThorsten Brants. 2000. TnT–A statistical part-ofspeechtagger. In Proceedings of Association forNeuro-Linguistic Programming (ANLP), pages 224–231.Eric Brill. 1995. Transformation-based error-drivenlearning and natural language processing: A casestudy in part-of-speech tagging. Computational Linguistics,21(4):543–565.