Database Modelling and Normalization for Desklib

ISYS114 2018 – ASSIGNMENT ONE
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Task 1: ER Diagram
Entity relationship diagram denotes to diagram essential to modelling of databases from
basic notifications to complex and confusing database. ER diagram are used as the
foundation of for logical data modelling. Additionally, they are used as the formation of
commonality as the basis of data modelling integration.
ER Diagram uses the following entity symbols:
An entity denotes to a concept or object that represents an idea
Entity symbol Name Description
Attribute An attribute is a feature/
characteristic of an object.
Derived attribute These are attributes whose
final value can be
calculated. For instance in
the diagram below, net
salary can be arrived at by
minus taxes from gross
salary and adding grief
allowances.
Multivalued attribute These are attributes that
can take more than one
value. For instance name
can take first name and last
name
Relationship This is an association among
objects.
Weak relationship This is an association of
weak entity with another
weak object.
Strong entity This is a parent entity as it
has weak entities that
depend on it.
Weak entity This is an entity that is
dependent on another
entity called strong entity
Associative entity An associative entity
contains features specific to
relationship among the
entities.

It should be noted that primary key attributes are indicated by use of underline. Whereas
foreign keys are represented with being in italic.
Task 2: EER Diagram
EER (enhanced entity relationship diagram) denotes to specialized Entity relationship
diagram that be used to model our database. This is higher level model that can be
deployed to represent most complex requirements of a database. EER diagrams
encompasses all attributes of an ERD together with the following:
 Union type or category
 Specialization and generalization: generalization denotes to the technique of reference of
a general entity whereas specialization is the vice versa.
 Super types and subtypes: a super type relates to one or more subtypes whereas a subtype
is a small group of entities with exceptional attributes.
 Relationship and attribute inheritance: is a concept of subtype entities inheriting values of
all super type.
