A hybrid approach to Urdu verb phrase chunking

A variety of verb phrases exist in Urdu including simple verb phrases, conjunct verb phrases and compound verb phrases. This paper explains the structure of Urdu verb phrases, and details a series of experiment to automatically tag them. Initially, a rule based model is developed using 21 linguistic rules for automatic VP chunking. A 100,000 word Urdu corpus is manually tagged with VP chunk tags. The corpus is then used to develop a hybrid approach using HMM based statistical chunking and correction rules. The technique is enhanced by changing chunking direction and merging chunk and POS tags. The automatically chunked data is compared with manually tagged held-out data to identify and analyze the errors. Based on the analysis, correction rules are extracted to address the errors. By applying these rules after statistical tagging, further improvement is achieved in chunking accuracy. The results of all experiments are reported with maximum overall accuracy of 98.44% achieved using hybrid approach with extended tagset.