Normalization

Normalization

Now comes a lot of rules and constraints, we call it Normalization. It is again applied at various level and are numbered as below

1NF

The first normal form asks the attributes to be atomic - means a column should contain only one piece of information. We should not save the say employee ID card number and employee number in single column separated by some separator. The schema we have is already in 1NF

2NF

The 2NF is a rule on primary key. No column should be dependent on subset of primary key. This will be maintained in most cased with the help of auto-increment id acting as primary key

3NF

The 3NF says, all the values in a table should be fully dependent on the primary key only. Or in other words,  a column in a table should not be obtained based another column(s) in the same table. So in our case employee_id/card_number in  swipe details and attendance register are mutually dependent. If you know one, you can get the other from employee entity. So we will have to remove employee id or card number. Employee id being the key identifier for employee table, I would prefer to save employee id over card number(also card number is string which occupies more space and searching is slower compared to searching numbers). 

When I started career, I always tried to do normalization. But now I understand, these are guidelines and not rules. More you learn the database and your application, you will find an excuse not to follow these. If you are interested, read more on the same.