<P> CLAWS pioneered the field of HMM - based part of speech tagging, but was quite expensive since it enumerated all possibilities . It sometimes had to resort to backup methods when there were simply too many options (the Brown Corpus contains a case with 17 ambiguous words in a row, and there are words such as "still" that can represent as many as 7 distinct parts of speech (DeRose 1990, p. 82)). </P> <P> HMMs underlie the functioning of stochastic taggers and are used in various algorithms one of the most widely used being the bi-directional inference algorithm . </P> <P> In 1987, Steven DeRose and Ken Church independently developed dynamic programming algorithms to solve the same problem in vastly less time . Their methods were similar to the Viterbi algorithm known for some time in other fields . DeRose used a table of pairs, while Church used a table of triples and a method of estimating the values for triples that were rare or nonexistent in the Brown Corpus (actual measurement of triple probabilities would require a much larger corpus). Both methods achieved accuracy over 95% . DeRose's 1990 dissertation at Brown University included analyses of the specific error types, probabilities, and other related data, and replicated his work for Greek, where it proved similarly effective . </P> <P> These findings were surprisingly disruptive to the field of natural language processing . The accuracy reported was higher than the typical accuracy of very sophisticated algorithms that integrated part of speech choice with many higher levels of linguistic analysis: syntax, morphology, semantics, and so on . CLAWS, DeRose's and Church's methods did fail for some of the known cases where semantics is required, but those proved negligibly rare . This convinced many in the field that part - of - speech tagging could usefully be separated out from the other levels of processing; this in turn simplified the theory and practice of computerized language analysis, and encouraged researchers to find ways to separate out other pieces as well . Markov Models are now the standard method for part - of - speech assignment . </P>

What part of speech is the word hidden