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CHAPTER 3: NORMALIZATION & ERD, HAFIQ RASHDAN BIN RASHIDI, MOHD HAZIQ…
CHAPTER 3: NORMALIZATION & ERD
An Entity Relationship Model
is a detailed, logical representation of the data for an organization or for a business area
is expressed in terms of entities in the business environment
can be used are Chen and Crow Feet.
Chen
Crow Foot
Basic Elements Of E-R Model
ENTITY
is a person, a place, an object, an event or a concept in the user environment about which the organization wishes to maintain data.
noun name
ATTRIBUTE
description or an entity characteristic
to differentiate object in an entity
RELATIONSHIP
the link between entities
use lowercase letters
RELATIONSHIP TYPE
CADINALITY= M:N
One occurrence in entity B is associated to many occurrence in entity A
one occurrence in entity A is associated to many occurrence in entity B
CARDINALITY= 1:M
RECURSIVE
/UNARY
Recursive/Unary
Relationship involving
only one entity.
BINARY
Binary
Relationship is a relationship between
two entities
.
TERNARY
Ternary
Relationship is simultaneous relationship between the
three entities
.
Apply ER diagrams in database development
3.2
(FAIRUL)
COMPOSE ENTITY
The many-to-many relationship identified in an E-R model shows a complex relationship
This can be simplified by transforming relationship to an entity known as Composite Entity.
Eg: DOCTOR treat PATIENT.
(davelyn)
THE M:N relationship between STUDENT and CLASS
visio does not permot the definition of a M:N relationship. to make this illustration, two 1:M relationship have been superimposed
Entity Type
STRONG ENTITY
A strong entity is one that exists independently of other entity
Symbol = rectangle
WEAK ENTITY
Symbol = double rectangle
The existence of a weak entity depends on the existence of strong entity.
HAFIQ RASHDAN BIN RASHIDI
MOHD HAZIQ IMAN BIN ROSLI
