18. A computer-implemented method of processing a natural language input for use in completing a task represented by the natural language input, comprising: generating a feature vector based on the natural language input; performing statistical classification on the feature vector with a processor to obtain a class identifier identifying a target class associated with the natural language input, the statistical classification being performed by performing statistical classification on the natural language input using a plurality of different statistical classifiers, and selecting the class identifier output by a greatest number of the plurality of statistical classifiers as representing the target class; selectively activating grammar rules in a grammar used in a rule-based analyzer, the activated grammar rules corresponding to the class identifier; and analyzing the natural language input with the rule-based analyzer using the grammar with the activated grammar rules to generate semantic expressions from the natural language input to fill semantic slots in the target class.
18. A computer-implemented method of processing a natural language input for use in completing a task represented by the natural language input, comprising: generating a feature vector based on the natural language input; performing statistical classification on the feature vector with a processor to obtain a class identifier identifying a target class associated with the natural language input, the statistical classification being performed by performing statistical classification on the natural language input using a plurality of different statistical classifiers, and selecting the class identifier output by a greatest number of the plurality of statistical classifiers as representing the target class; selectively activating grammar rules in a grammar used in a rule-based analyzer, the activated grammar rules corresponding to the class identifier; and analyzing the natural language input with the rule-based analyzer using the grammar with the activated grammar rules to generate semantic expressions from the natural language input to fill semantic slots in the target class. 19. The method of claim 18 and further comprising: prior to performing statistical classification, identifying words in the natural language input that have semantic content.