45
There are
four relationships available
in
Entity
Relationship Diagram to
represent each on the data entities:
One to one (1:1) relationship
One to one relationship
means that one and the only one entity can be
use with one and the only one of the other entity. For instance, one ID
card number is present one and the only one of people.
One to many (1: M) relationship
One
to
many
relationship means
one
and
the
only
one
entity
can
be
associated with many entities. For instance, one consultant firm can be
use by many clients or customer.
Many to
many (M: M) relationship
Many
to
many
relationship
means
multiple
of
entities
can
be
use
by
many
or
multiple
entities.
Mostly,
many
to
many
relationships
are
use
it when there are two related entities (one to many relationships). For
instance, one staff in Auditor Company could have two or many
company to be auditing it.
Mandatory relationship
8
Mandatory
relationship is if one entity occurrence requires a
corresponding entities occurrence in a particular relationship.
Optional relationship
4
8
Peter Rob, Carlos Coronel. 2004, ‘Entity Relationship
(ER) Model’, in Database Systems: Design,
Implementation,
and Manageme nt, Thomson Course Technology, United State America, pp 135 -136.
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