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Data Management {CLASS XI}

Q: What is a Database?

The collection of data is usually referred to as the DATABASE.

The database maintains the information that help to the decision-making process in an organization.

The same data in a database may serve many application.

e.g.:A database of employees of an organization, Database of students of a school, etc.

Database System

It is basically a computer based record keeping system.

The Relational Data Model

In Relational data model, the data is organized into tables ( i.e. rows & cols). These tables are called relations. A row in a table represents a relationship among a set of values.

Terminology in RDBMS

The different terms used in the relational model are:
1.Relation
2.Tuples
3.Attributes
4.Degree
5.Cardinality
6.Domain

1. Relation

A Relation is a table (i.e rows & cols)
In above example (STUDENT) is a relation that has 4 rows (records) and 3 columns (fields).

2. Tuples

The rows of a relation are generally referred to as Tuples.

In above example there are 4 tuples (rows).

3. Attributes

The columns of a relation are generally referred to as Attributes.

In above example there are 3 attributes (cols).

4. Degree

The Number of attributes(cols) in a relation is referred to as the degree of the relation.
In above example there are 3 attributes (cols), hence, it is a relation of degree 3.

5. Cardinality

The No of tuples (rows) in a relation is referred to as the cardinality of the relation.

In above example there are 4 tuples (rows), hence, the cardinality of the relation is 4.

6. Domain.

A Domain is the pool of values from which the actual values appearing in a given column are drawn.

In above example the domain of Cat column is (OBC, SC, ST, Gen), and domain of Gender column is (Male, Female)

Keys:

keys are of three types

•Primary Key
•Candidate Key
•Alternate Key
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