Dimension tables is de-normalized in the nature

Question

Clarify briefly why dimension tables is de-normalized in the nature?

Answer 1

Since in the Data warehousing past data must be maintained, to uphold past data means assume one employee details such as where previously he worked, and currently where he is working, all details must be maintain in the single table, if you maintain primary key it won't let the duplicate records with similar employee id. So to maintain past data we are all going for concept data warehousing by using surrogate keys we can achieve the historical data (by using oracle sequence for critical column).

So all the dimensions is marinating past data, they are de-normalized, due to duplicate entry means not accurately duplicate record with similar employee number another record is maintaining in table.