Parsing: The Problem of Finding a Derivation

Parsing: The Problem of Finding a Derivation

1. Given a grammar G and a string that one believes is a member of L(G) there are two basic ways that one can attempt to find a derivation of from S.

   Top-down parsing

   Begin with the start symbol of G and repeatedly substitute the left hand side of a production for a non-terminal until the start symbol has been rewritten to match .

   Bottom-up parsing

   Begin with and repeatedly "simplify" the string by replacing a sub-string that matches the right hand side of a production by the non-terminal on its left hand side until has been simplified to S.

2. In our discussion we will make the assumption that we want to produce derivations "on-the-fly". That is, that we do not want to hold the entire input string in memory but wish to generate a derivation while making a single pass through the input string.

Parsing: The Problem of Finding a Derivation