 The tagging system, named CLAWS, went through improvements to yield the latest CLAWS4 system, which is used for tagging the BNC.CLAWS1 was based on a hidden Markov model and, when employed in automatic tagging, managed to successfully tag 96% to 97% of each text analyzed.CLAWS1 was upgraded to CLAWS2 by removing the need for manual processing to prepare the texts for automatic tagging.