A relation between two tables such that one primary key value corresponds to one foreign key value is known as one-to-one relationship. In other words, each record in parent table is related to one and only one record in child table is one-to-one relationship.

A relation between two tables such that one primary key value corresponds to many foreign key value is known as one-to-many relationship. In other words, each record in parent table is related to zero or many records in child table is one-to-many relationship.

A relationship where many instances of an entity are associated with many instances of another entity is known as many-to-many relationship. Consider the enrollment relationship between a student and a class tables. A single student may be enrolled in many classes and a single class may enroll many students.

If the primary column is contributed to the child table's primary key or in other words, the foreign key is one of the columns in the child table's primary key, then this relationship is called an identifying relationship.

The advantages of normalizing database are:
- Dependencies between data are identified.
- Redundant data and all of the problems associated with it is minimized
- The data model is flexible and easier to maintain.