List Two Reasons Why Null Values Might Be Introduced Into The Databas

1.	List Two Reasons Why Null Values Might Be Introduced Into The Database?
Answer» Nulls may be introduced into the database because the actual value is either unknown or does not exist. For example, an EMPLOYEE whose address has CHANGED and whose NEW address is not yet known should be retained with a null address. If employee tuples have a composite attribute dependents, and a particular employee has no dependents, then that TUPLE’s dependents attribute should be given a null value. Nulls may be introduced into the database because the actual value is either unknown or does not exist. For example, an employee whose address has changed and whose new address is not yet known should be retained with a null address. If employee tuples have a composite attribute dependents, and a particular employee has no dependents, then that tuple’s dependents attribute should be given a null value.

List Two Reasons Why Null Values Might Be Introduced Into The Database?

Answer»

Nulls may be introduced into the database because the actual value is either unknown or does not exist. For example, an EMPLOYEE whose address has CHANGED and whose NEW address is not yet known should be retained with a null address. If employee tuples have a composite attribute dependents, and a particular employee has no dependents, then that TUPLE’s dependents attribute should be given a null value.

Nulls may be introduced into the database because the actual value is either unknown or does not exist. For example, an employee whose address has changed and whose new address is not yet known should be retained with a null address. If employee tuples have a composite attribute dependents, and a particular employee has no dependents, then that tuple’s dependents attribute should be given a null value.

Discussion

No Comment Found

Related InterviewSolutions

Discuss The Advantages And Disadvantages Of The Two Methods That We Presented In Section 19.5.2 For Generating Globally Unique Time Stamps?
Give An Example Where Lazy Replication Can Lead To An Inconsistent Database State Even When Updates Get An Exclusive Lock On The Primary (master) Copy?
Explain The Difference Between Data Replication In A Distributed System And The Maintenance Of A Remote Backup Site?
Explain The Notions Of Transparency And Autonomy. Why Are These Notions Desirable From A Human-factors Standpoint?
When Is It Useful To Have Replication Or Fragmentation Of Data?
How Might A Distributed Database Designed For A Local-area Network Differ From One Designed For A Wide-area Network?
Explain How The Following Differ: Fragmentation Transparency, Replication Transparency, And Location Transparency?
Discuss The Relative Advantages Of Centralized And Distributed Databases?
Consider A Network Based On Dial-up Phone Lines, Where Sites Communicate Periodically, Such As Every Night. Such Networks Are Often Configured With A Server Site And Multiple Client Sites. The Client Sites Connect Only To The Server, And Exchange Data With Other Clients By Storing Data At The Server And Retrieving Data Stored At The Server By Other Clients. What Is The Advantage Of Such An Architecture Over One Where A Site Can Exchange Data With Another Site Only By First Dialing It Up?
Consider A Bank That Has A Collection Of Sites, Each Running A Database System. Suppose The Only Way The Databases Interact Is By Electronic Transfer Of Money Between One Another. Would Such A System Qualify As A Distributed Database? Why?