1. Entity and referential integrity : Use of Primary and Secondary Key, to prevent NULL entries and also to ensure that all entries are unique
2. Functional Dependency: Employee name is functionally dependent on  Unique Social Security Number
3. Normalization
   1. 1st Normal Forms : Each table should have a primary key
       

      Name	DEPT-1	DEPT-2	DEPT-3	DEPT-4
      A	X
      B		X
      C			X
      D				X

      Normalized

      Name	DeptN0
      A	1
      B	2
      C	3
      D	4

   2. 2nd Normal Form
       

      STDid	SADDR	SName
      S1	A1	XYZ
      S2	A2	XYZ
      S4	A4	MNO
      S3	A3	ABC

       

      STDID	SUBJECT
      S1	ENG
      S2	ENG
      S4	MATH
      S3	HISTORY

   3. 3rd Normal Forms.

•  A process of  ensuring data integrity and eliminating data redundancy.
  • – Data integrity : consistent and satisfies data constraint rules.
•  Normalization should remove redundancy, but not at the
  expense of data integrity.

• An integrity enforce a rule that restricts the input of values/attributes of a set of data present in a DB
  •  entity integrity - The rows (or tuples) in a relation represent
    entities, and each one must be uniquely identified. Hence the master table must have the primary key, that must have a unique non-null value for each row.
  • referential integrity - This constraint imports a reference of a row in the master table as a  foreign key. Thus a relationship is enforced between two tables.

In a one-to-one relationship, each record in one table relates directly to a single record in another table.

An example is an Employees table and a company Soccer Players table. An employee will be listed in the Soccer Players table only once, and vice versa. Each soccer player has one matching record in the Employees table. This set of data is a subset of the Employee ID records in the Employees table. 

1. Each soccer player has one matching record in the Employees table.
2. This set of data is a subset of the Employee ID records in the Employees table.
    

In a one-to-many relationship, a record in one table relates to multiple records in a second table, but the records in the second table relate to only one record in the first table.

An example is a Suppliers table and a Products table. One supplier might be the only source of multiple products, all of which relate only to that supplier.
 

1. Figure 1 One supplier ...
2. Figure 2 can supply more than one product ...
3. Figure 3 ... but each product has only one supplier

In a many-to-many relationship, a record in one table relates to multiple records in a second table, and a record in the second table relates to multiple records in the first table.

This type of relationship requires a third table, called a junction table. The junction table refers the primary key in the master table,  with (one or more) foreign keys.

For example, the Orders table and the Products table have a many-to-many relationship. One order can contain many products, and each product can appear in many orders.

The third table — in this example, the Order Details table — contains primary keys from the Orders and Products tables. The Order Details table is the junction table for the other two.

 All junction tables connect tables that have one-to-many relationships with the junction tables, and the primary keys of those connected tables are the foreign keys of the junction table.

When one table can relate to many others simply by referencing information in them, the parts of your database are like the cells of your body. Each is active, each is the right size for its business, and together they can achieve effects vastly beyond their individual abilities.
  

1.  Primary key from the Orders table.
2. Primary key from the Products table.
3. One order can have many products ...
4. and each product can appear on many orders