Relational Data Model Video Lecture - SSC CGL Tier 2 - Study Material,

hello French welcome back in this
tutorial we will study about relational
model relational model represents the
database as a collection of relations a
relation is considered as a table of
values and a row in a table represents a
fact corresponding to real-world entity
or relationship the name of table and
the name of columns are used to help to
interpret the meaning of the values in
each row of table for example see this
employed table each row of this table
represents a fact about an employee and
Kitty the column names name age assassin
and Department specify how to interpret
the data values in each row on the basis
of column each value is in in relational
model terminology that table is called a
relation Rho is called a tuple and
column headers are called attributes
the set of allowed values for an
attribute is called the domain of that
attribute for example for attribute
Department the domain is the set of all
department needs a relation is defined
as a set of tuples relation is not
sensitive to the order of doubles
next is relation schema a relation
schema is used to describe a relation a
relation schema is made up of our
relation name and list of attributes for
example see this relation schema here
student is the name of relation and name
class and rule number are the attributes
the degree of a relation is the number
of attributes of its relation schema
each value in a temple of a relation is
an atomic value it means value in a
temple is not divisible into components
has composite and multivalued attributes
are not allowed a special value called
null is used to represent the values of
attributes that may be unknown or may
not apply to a temple for example some
student temples have null for their
office phone numbers because office
phone number doesn't apply to these
students they don't have an office if a
student has a null for home phone then
it is because either he doesn't have a
home phone or he has one but we don't
know it thank you very much
you