Constraints Vs Rules in sql server

Constraints:
Constraints are the condition provided on a column. If the column gets deleted by default, my constraint will get deleted.
Before applying the constraint the column should satisfy the condition.If i try to put a constraint on this column like the column should be unique, then my compiler will indicate an error like its not possible to create the constraint.

Rules:
Rules are nothing but the condition or terms created in the database and the column or table who want to implement that rule can use it.
If your trying to bind the rule with my column it wont think about your past data in the table and will try to abide for the future data