Chapter 3

Question 1

What are the properties of a relation?

Answer 1

A table is a two-dimensional structure with rows and columns.
Each row represents a single entity occurrence, and all rows must be unique.
Each column represents an attribute with a distinct name.
Each cell contains a single atomic value.
All values in a column must be of the same data type.
Each column has a defined range of values, called the domain.
The order of the rows and columns doesn’t matter.
Each table must have a unique identifier for each row.

Question 2

What are the 2 most important properties of the relational model?

Answer 2

Degree - number of its attributes.
Cardinality - number of its tuples.

Question 3

What is a composite key?

Answer 3

It is a key composed with more than one attribute.

Question 4

What is a superkey?

Answer 4

It is any key that uniquely identifies each row.

Question 5

What is a candidate key?

Answer 5

It is a super key without any redundancies, a minimal super key

Question 6

What is a primary key?

Answer 6

Unique identifier for each row in a database table.