Formal grammar

• Formal grammar is a set of rules. It is used to identify correct or incorrect strings of tokens in a language. The formal grammar is represented as G.
• Formal grammar is used to generate all possible strings over the alphabet that is syntactically correct in the language.
• Formal grammar is used mostly in the syntactic analysis phase (parsing) particularly during the compilation.

Formal grammar G is written as follows:

G = <V, N, P, S>  

Where:

N describes a finite set of non-terminal symbols.
V describes a finite set of terminal symbols.
P describes a set of production rules
S is the start symbol.

Example:

1. L = {a, b}, N = {S, R, B}

Production rules:

1. S = bR  
2. R = aR  
3. R = aB   
4. B = b
5. 
   

Through this production we can produce some strings like: bab, baab, baaab etc.

This production describes the string of shape banab.

      Fig: Formal grammar