[NAME]
ALL.dao.grammar.notation

[TITLE]
Grammar Notations

[DESCRIPTION]

Syntax definition: A ::= B, A is defined as B , which can be a descriptive sentence or a
combination  of the following definition items, 
  1. Token: 'token'
  2. Descriptive: "description"
  3. Alternative: S | Y
  4. Optional: [ S ]
  5. Grouping: ( S )
  6. Repeating: S * or S + 
       *  * : zero or more times;
       *  + : once or more times;  
     For convenience, { S } is also used to represent repeating  of S for zero or more ti
     mes. 


Examples, 
  *  ( S | Y )+ represents all the possible sequences composed   of S and Y, such as: S; 
     Y; SY; YS; SSY ...
  *  S ( Y | N ) T represents: S Y T   or S N T