1. There shoudl be one-one relatiionship b/w instance of entity and row in a table
2. A field should have same meaning in each row.
3. Each table represents atmost one entity.
4a. Multiple instance of entity represents by multiple rows in a table.
4b. Multiple instance of entity should not be represents as multiple table.
5. Joins should be based only on primary foreign key equality.
6. keys should links correctly.