Parsing is a generic operation that identifies legal expressions and breaks them up into a form suitable for further processing. Parsing has applications in many different fields such as computer science, Interpreting human language, and so on. The main goal of parsing is to check the validity of an expression and make more sense out of it. The term �grammar� is commonly used in programming languages to identify legal expressions. There are two approaches commonly used during parsing of these two methods : > Top-down approach: This method looks at the program first, and recursively identifies parts that are eventually matched to the input expression. > Bottom-up approach: This method looks at the input expression and combines the pieces of the expression to make a legal program from it.