Database Concepts

Question 1

What is an entity?

Answer 1

An entity is a person, place, thing, or event that a business needs to know about. Some examples are people, customers, parts, orders, etc.

Question 2

What is an attribute?

Answer 2

A property of an entity. i.e. if an entity is a person then an attribute may be sex, eye color, height, etc.

Question 3

What is an entity set?

Answer 3

A collection of entities. i.e. a table of person entities.

Question 4

What is an entity instance?

Answer 4

A single entity. i.e. a person in a table of persons.

Question 5

The concept of an entity is equal to [blank] in database terminology.

Answer 5

table

Question 6

An attribute is equal to [blank] in database terminology.

Answer 6

column

Question 7

An instance of an entity is equal to [blank] in database terminology.

Answer 7

record or row.

Question 8

implementing a database requires two steps. What are they?

Answer 8

Physical and logical.

Question 9

What is involved in the logical design step of implementing a database?

Answer 9

It is the planning out phase before actually coding. Getting the abstract design of the database created.

Question 10

What is involved in the physical design of the database?

Answer 10

The actual software implementation of tables and columns that are used to represent their real world counterparts.

Question 11

The way to store an attribute about an entity depends on what?

Answer 11

The needs of the business.

Question 12

What is a simple valued attribute?

Answer 12

Only one component makes up the value. It is the simplest breakdown of the data. i.e. John or “sue ann” for first name field.

Question 13

What is a composite valued attribute?

Answer 13

Multiple components make up the value. i.e. “John Wayne Smith”. If a component is missing, then you cannot determine the value.

Question 14

What is a derived attribute?

Answer 14

Not actually stored in the table, but calculated from data in the table.

Question 15

What is a single valued attribute?

Answer 15

A column/row intersection in a table where only one value can be stored. i.e. a person entity instance can only have one birth date.

Question 16

What is a multi-valued attribute?

Answer 16

A column/row intersection in a table where there may be many values. A single employee can have many dates on when they were paid.

Question 17

Multi-valued columns are bad. Why is this so?

Answer 17

It cannot be easily implemented in a relational database. Causes storage and retrevial problems. When one customer has many rentals, storing the multiple rentals in a single cell can be problematic. Relationships need to be established to reference this information instead.

Question 18

Can a value be both simple and composite at the same time?

Answer 18

no

Question 19

Can a value be both single and multi valued at the same time?

Answer 19

no

Question 20

Can a value be single and simple valued at the same time?

Answer 20

yes

Question 21

Can a value be simple and multi valued at the same time?

Answer 21

yes, but it is bad. Don’t do it. i.e. rental number stored in customer table.

Question 22

Can a value be composite and single at the same time?

Answer 22

Yes. i.e. date of birth.

Question 23

Can a value be composite and multi valued at the same time?

Answer 23

Yes, but it is bad. Don’t do it. i.e. rental date stored in customers table.

Question 24

What are business rules?

Answer 24

rules about how the business operates that dictates the database design. Should be done before design in order to implement correctly.

Question 25

What are the different key types in a database?

Answer 25

Primary, Foreign, Candidate, Secondary

Question 26

What is a primary key?

Answer 26

A unique attribute(s) about an entity that does not change that can be used to uniquely identify an entity instance.

Question 27

Can two records in a table have the same primary key?

Answer 27

No.

Question 28

What is a candidate key?

Answer 28

An attribute that could be used as a primary key.

Question 29

Can a primary key be more than one column?

Answer 29

Yes. It can be, provided both columns are unique to that record.

Question 30

What is an artificial key?

Answer 30

A key that is generated by the business, made up. It could be an auto generated number.

Question 31

What is a secondary key?

Answer 31

They candidate keys that are left over after a primary key has been selected.

Question 32

What is a foreign key?

Answer 32

A primary key in one table that is added to another table to establish a relationship between the records. There can be any number of foreign keys in a table.