Databases

Question 1

Explain entity

Answer 1

a noun - person, place, thing or idea and used as the name of tables

Question 2

Attribute

Answer 2

they are columns in tables and represent different characteristics of each entity

Question 3

Explain relationship

Answer 3

represents the associations between the tables

Question 4

Explain relation

Answer 4

a table

Question 5

Explain relational database

Answer 5

A database full of relations (tables)

Question 6

What is functional dependence?

Answer 6

When column B is functionally dependent on column A, it means that the values in column A determine the values of column B

Question 7

What does A–>B mean?

Answer 7

It means that B is functionally dependent on A

Question 8

Explain the term primary key

Answer 8

It means that there is one column or a collection of columns that can determine the rest of the columns - uniquely identifies the records of the table

Question 9

Can primary key have a null value?

Answer 9

No

Question 10

Explain the term candidate key

Answer 10

Candidate key is closely related to primary key - a candidate key is one of two or more columns that could function as a primary key for the table

Question 11

What is an unnormalized relation?

Answer 11

It is a table (relation) that satisfies the criteria for a relation but may contain repeating groups

Question 12

Definition of normal form

Answer 12

A table in normal form possesses a certain desirable collection of properties

Question 13

Explain normalization

Answer 13

a process in which you identify the existence of potential problems, such as data duplication and redundancy, and implement ways to correct these problems.

Question 14

Explain first normal form

Answer 14

A table is in 1NF when it does not contain a repeating group

Question 15

What is concatenation?

Answer 15

connected columns (fields)

Question 16

When is a table in second normal form?

Answer 16

A relation is in second normal form when it is already in first normal form and no nonkey column is dependent on only a portion of the primary key

Question 17

What is a nonkey column

Answer 17

A nonkey column is a column that is not part of the primary key

Question 18

When is the relation automatically in second normal form (2NF)?

Answer 18

When the primary key of a relation contains only a single column

Question 19

Name the four categories of update anomalies

Answer 19

Updates; Inconsistent data; Additions; Deletions

Question 20

Explain the term determinant

Answer 20

Any field (or collection of fields that determine another field is called a determinant i.e. the primary key and therefore any candidate key

Question 21

When is a relation in third normal form (3NF)?

Answer 21

A table is in third normal form when it is in second normal form and the only determinants it contains are candidate keys

Question 22

What is an entity-relationship diagram?

Answer 22

A diagram that shows the relationships between the entities

Question 23

There are 3 ways to represent entities and relationships in an E-R diagram. Explain them

Answer 23

1) An arrow which represents a one-to-many relationship
2) A crow’s foot which represents a one-to-many relationship
3) Inserting a diamond-shaped figure that explains the relationship between the entities

Question 24

What is a field?

Answer 24

A field refers to columns

Question 25

What is a record (tuple)?

Answer 25

It refers to the rows in tables

Question 26

What does it mean to qualify column names?

Answer 26

It refers to when you are working with two or more relations that have common columns. So, you specify which column you are referring to by indicating which relation you are talking about before you specify which column you are working with