grammar rules

Grammar rules map non-terminal symbols (such as SENTANCE or NOUN_PHRASE) expressing phrases or logical groups of words into other non-terminals and terminal symbols often single words (such as 'dog'). There are usually several rules for a given non-terminal symbols. For example a simple SENTANCE might consist of a NOUN_PHRASE VERB_PHRASE (such as "the dog sat"), or NOUN_PHRASE VERB_PHRASE NOUN_PHRASE (such as "the girl ate the apple").