Why do we use normal form(like Conjuctive Normal Form and Disjunctive Normal Form) in Artificial intelligence?What is the specific purpose of Making a sentence in Normal Forms?
The point of normalizing forms is for consistency between expressions. It makes identical expressions easier to spot, and makes reasoning and simplifying easier.
Conjunctive, disjunctive, or even propositional expressions are just different ways to say the same things.
Artificial intelligence is concerned with these logic forms only when the AI happens to perform logical operations. Most AI's use logic in some form.
Many algorithms, such as SAT solvers, are optimized for Conjunctive Normal Form.
See for instance http://minisat.se/