Question

Section IV. Please answer three of the following questions in 5-6 lines (100 words) (7X3 = 21 points)

a. What is data integrity, and what is the significance of a lack of data integrity?

b. What is the difference between controlled and uncontrolled redundancy?

c. What is the difference between logical and physical data independence?

d. Why is it useful to know all the candidate keys of a relation schema?

e. What is the difference between a desirable and an undesirable functional dependency? Describe the nature of the problems caused by undesirable functional dependencies. What prevents us from simply ignoring undesirable functional dependencies?

Answer 1

(a) Data integrity is the maintenance and the assurance of the accuracy and consistency of data over its entire life-cycle.

Unintentional changes or the deletion of parts of data may render the data useless. It is no longer accurate and reliable, as it is different from its original form.

(B)Redundancy refers to duplicacy of data in the same database.

Controlled Redundancy:

It refers to sorting the redundancy as soon as the input is given.

Although maximum platforms do not support controlled redundancy.

Un-Controlled redundancy:

It is an inconsistent state which cannot be sorted or controlled.

It is the most common occurring and realistic situation.

(C)Physical Data Independence Logical Data Independence

It mainly concern about how the data is stored into the system. And It mainly concerned about the structure or the changing data definition.

It is concerned with the internal schema.and It is concerned with the conceptual schema.

(D)Candidate Key can be any column or a combination of columns that can qualify as unique key in database. There can be multiple Candidate Keys in one table. Each Candidate Key can qualify as Primary Key.

(E)desirable changes: the changes which are desirable (need) to be change are called an desirable changes. undesirable changes: the changes which are not desired to change is called undesirable changes. Changes that benefit us are called desirable changes.