Reference from http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form A BNF specification is a set of derivation rules, written as <symbol> ::= __expression__ where <symbol> is a nonterminal, and the __expression__ consists of one or more sequences of symbols; more sequences are separated by the vertical bar, ‘|’, indicating a choice, the whole being a possible substitution for the symbol on […]

Just a reference from here http://en.wikipedia.org/wiki/Context-free_grammar A context-free grammar G is defined by the 4-tuple where is a finite set; each element is called a non-terminal character or a variable. Each variable represents a different type of phrase or clause in the sentence. Variables are also sometimes called syntactic categories. Each variable defines a sub-language […]