Relational Database

Question 1

What is a database?

Answer 1

A well-organised collection of data
that are related in a meaningful way,
describing a domain of interest
(a collection of relations)

Question 2

What is a relational database?

Answer 2

Focus on things in the
domain of interest and the relations between
them

Question 3

What is a database management system?

Answer 3

Software that helps
maintain and utilise large collections of data in an
efficient manner

Question 4

What are the advantages of a database management system?

Answer 4

Data independence
 Efficient data access
 Data integrity
 Concurrent access and recovery from crashes

Question 5

What does a relation consist of?

Answer 5

Relation schema: describes the format of a table,
consisting of:
• Relation’s name
• Name of each field (column)
• Domain of each field
 Relation instance: the content of a table
• A set of tuples (records)

Question 6

What is Arity?

Answer 6

Also called degree

Number of fields

Question 7

What is Cardinality?

Answer 7

Number of rows

Question 8

What is Structured Query Language?

Answer 8

Standard language
for creating, manipulating and querying data in
relational database management systems

Question 9

What is Data Definition Language?

Answer 9

Subset of SQL that

allows us to create, delete and modify tables

Question 10

How do you create relations with DDL?

Answer 10

CREATE TABLE declaration: define a new relation
(called ‘table’ in SQL) with a particular schema
CREATE TABLE table-name (
⟨attribute declarations⟩
⟨integrity constraints⟩
)

Question 11

What is Domain constraint?

Answer 11

For each row in this table, the
values in each column must be drawn from the
appropriate domain
-Condition of the database

Question 12

What are the integrity constraints?

Answer 12

• Key constraints

- Foreign key constraints

Question 13

What is the Primary key?

Answer 13

-Uniquely identifies a tuple
-No 2 rows in the table have the same mn
PRIMARY KEY (mn)

Question 14

What is the Foreign key?

Answer 14

Specify links between tables
Will always take a value that appears in the table you choose
FOREIGN KEY (mn) REFERNECES Course
The foreign key in a referencing relation must match
the primary key of the reference relation.
• Same number of columns and same domains.

Question 15

What should happen if a row in the table is deleted?

Answer 15

1. All rows in Takes that refer to it should be deleted (ON DELETE CASCADE)
2. For each row in Takes that refer to it, set its mn value to some pre-specified default value (ON DELETE SET DEFAULT)
3. For each row in Takes that refer to it, set its mn value to null (ON DELETE SET NULL)