2.2 BASIC CONCEPTS OF DATABASE SYSTEMS

2.2 BASIC CONCEPTS OF DATABASE SYSTEMS

Data Hierarchy

1. A database contains a data structure to store data.

2. The hierarchy of data in a database is as follows:

a) Database is a collection of tables¹.

Example:

A college database contains Student, Course and Result tables.

b)  A table is a file which contains a set of records.

Example:

i. Student table contains records of particulars of all students.

ii. Course table contains records of particulars of all courses offered.

iii. Result table contains records of marks obtained by students for a particular course in a particular test or exam.

c) A record is a row of values. A record is also called a tuple.

Each record represents an object in the real world.

d) Each value in a record belongs to a field. Each field has a specific data type, size, format and constraints.

Examples:

A student record contains fields such as Name, ID and CGPA.

The values belonging to the same field in a table are all of the same data type.

Example:

ID is group of characters defined by type, size, format and constraints. It is a text of 5-character size, displayed as numerical digits and must be within the range of 0 to 99999.

e) Each value contains characters. A character can be a letter, a number or a symbol.

^1. A table also known as a relation.