Grammars can be used for two different purposes in speech-based apps that are as follows:
Speech recognition: In this case, grammars (also known as language models) specify the words and phrases that the recognizer can expect. For example, if the system is dealing with cities, it should not try to recognize numbers. Speech recognition grammars, as defined by W3C available at http://www.w3.org/TR/speech-grammar/, can either be specified explicitly by the developer (hand-crafted grammars) or can be computed from language data (statistical grammars). Speech recognition grammars help to make speech recognition more accurate.
Natural language understanding: The idea is to take the output of the recognizer and assign a semantic interpretation (or meaning) to the words. This can be done in several ways. One method involves determining the structure of the sentence (syntactic analysis) and then assigning a semantic interpretation ...