Databases

Question 1

Define entity, attribute and relationship

Answer 1

Entity = Object, person, event or thing of interest which data is to be recorded

Attribute = A property of an entity

Relationship = Link between two entities

Question 2

3 types of relationships

Answer 2

One-to-one
One-to-many
Many-to-many

Question 3

Define flat-file databases

Answer 3

Databases that use one entity

Question 4

Disadvantages of flat-file databases

Answer 4

Data inconsistency
Data redundancy
Inefficiency
Difficult to maintain

Question 5

Define relational databases

Answer 5

Databases with two or more linked tables

Question 6

Define key terms for relational databases:
Primary key
Foreign key
Referential integrity
Composite key

Answer 6

Primary key - Attribute that uniquely represents a record
Foreign key - Attribute in one table that is primary key in another
Referential integrity - Value that appears in a foreign key in one table,
must be a primary key in another
Composite key - Combination of two or more attributes together
(instead of a singular primary key)

Question 7

Define normalisation

Answer 7

Process of decomposing a flat-file into best relational database to minimise data redundancy

Question 8

Summary of normalisation process

Answer 8

1. Separate repeating groups into separate entities. Copy primary key as a foreign key
2. All non-key attributes checked to see if only dependent on primary key (if not, create new entity)
3. Tables with composite keys, ensure non-key attributes dependent on each part of the composite key (if not, create new entity)