句型句子和语言

 

Given a grammar G with start symbol S,we can use the =>* relation to define L(G),the language generated by G. Strings in L(G) may contain only terminal symbols of G.

We say a string of terminals w is in L(G) if and only if S =>* w . The string w  is called a sentence of G.

If  S =>* α ,wher α may contain nonterminals then we say that α is a sentential form of G