Unit 4 : Relational Database

Question 1

What does relational model enables programer to do?

Answer 1

1. To view data logically rather than physically

Question 2

What is the advantages of a table in the relational model?

Answer 2

1. Has the advantage of structural and data independence

Question 3

What does a table in the relational model resemble from conceptual point of view ?

Answer 3

1. A file

Question 4

What table is easier to understand its hierarchical and network database predecessors?

Answer 4

1. Relational Model

• Order
  1. Hierarchical
  2. Network
  3. Relational
  4. Entity Relationship

Question 5

What does table consists? ( 2 )

Answer 5

1. Rows
2. Columns

Question 6

What does entity set consists?

Answer 6

1. Contains group of related entities

Question 7

Why does table is also called as relation?

Answer 7

1. Because Codd used the term relation as a synonym for table

Question 8

What can we think table as?

Answer 8

1. A persistent relation ( A relation whose contents can be permanently saved for future use )

Question 9

What does keys consists?

Answer 9

1. Consists of one or more attributes that determine other attributes

• The key’s role is based on determination :
  
  • If you know the value of attribute A, you can look up ( determine ) the value of attribute B

Question 10

What is primary key?

Answer 10

1. An attribute ( combination of attributes ) that uniquely identifies any given entity ( row )

Question 11

What is a foreign key ?

Answer 11

1. An attribute whose values match primary key values in the related table

Question 12

What is secondary key?

Answer 12

1. Key used strictly for data retrieval purposes

Question 13

What is candidate key?

Answer 13

1. Any column or a combination of columns that can qualify as unique key in database

Question 14

What is referential integrity?

Answer 14

1. Foreign Keys contains a value that refers to an existing valid tuple ( row ) in another relation

• IT ensures that relationships between tables in a relational database remain consistent. It focuses on maintaining valid connections between primary keys (PK) and foreign keys (FK)

Question 15

Can we insert multiple candidate key ?

Answer 15

1. Yes , it can also qualify as primary key

Question 16

How to select primary key? ( 3 )

Answer 16

1. Select a key that does not contain null
2. Select a key that is unique and does not repeat
3. Make sure that primary key does not keep changing

Question 17

What has no data entry, not permitted in primary key and should be avoided in other attributes?

Answer 17

1. NULL

Question 18

What can NULL represent?

Answer 18

1. An unknown attribute value
2. A known, but missing, attribute value
3. A “not applicable” condition

Question 19

What problems can NULL create?

Answer 19

1. Create problems when functions such as COUNT, AVERAGE, and SUM are used
2. Can create logical problems when relational tables are linked

Question 20

What role does controlled redundancy play in a relational database?

Answer 20

1. Controlled redundancy makes the relational database work.

Question 21

How do tables within a relational database share information?

Answer 21

1. Tables within the database share common attributes that enable the tables to be linked together.

• Share common attributes that enable tables to be linked together

Question 22

When is the occurrence of multiple values in a table not considered redundant?

Answer 22

1. Multiple occurrences of values in a table are not redundant when they are required to make the relationship work

• When required to make the relationship work

Question 23

When does redundancy exist in a relational database?

Answer 23

1. Redundancy exists only when there is unnecessary duplication of attribute values.

• When unnecessary duplication of attribute values

Question 24

What is a data dictonary?

Answer 24

1. A data dictionary provides detailed accounting of all tables found within the user/designer-created database.

Question 25

What information does a data dictionary contain?

Answer 25

1. It contains at least all the attribute names and characteristics for each table in the system.

Question 26

What type of data does a data dictionary hold?

Answer 26

1. A data dictionary contains metadata—data about data.

Question 27

Why is the data dictionary sometimes described as "the database designer's database" ?

Answer 27

1. Because it records the design decisions about tables and their structures.

Question 28

What are the besic building blocks of a relational database

Answer 28

1. Tables

Question 29

List out the types of integrity rules ( 2 )

Answer 29

1. Entity Integrity 2. Referential Integrity

Question 30

What is the requirement of entity integrity?

Answer 30

1. All primary key entities are unique, and no part of a primary key may be null

Question 31

What is the purpose of entity integrity?

Answer 31

1. Each row will have a unique identity, and foreign key values can properly reference primary key values

Question 32

What is the requirement of referential integrity?

Answer 32

1. A foreign key may have either a null entry - as long as it is not a part of its table's primary key - or an entry that matches the primary key value in a table to which it is related

Question 33

What is the purpose of referencial integrity?

Answer 33

1. It is possible for an attribute NOT to have a corresponding value, but it will be impossible to have an invalid entry. The enforcement of the referential integrity rule makes it impossible to delete a row in one table whose primary key has mandatory matching foreign key in another table

Question 34

What is known for each column has a specific range of values ?

Answer 34

1. Attributes Domain