Give difference between top down parsing and bottom up parsing.

Top down parsing: Specified an input string, top down parsing tries to derive a string identical to this by successive application of grammar rules to the grammar's distinguished symbol. While such a string is acquired, a tree showing its derivation would be the syntax tree for an input string. Therefore if ? is input-string, a top-down parse finds a derivation sequence.

Bottom up parsing: This parse attempts to increase syntax tree for an input string by a sequence of reduction. If the input string can be decreased to the distinguished symbol, the string is valid. If string is not valid, error would be noticed and indicated during the process of reduction itself.