System analysis and design

SYSTEM ANALYS

IS AND

DESIGN

S A F A A S. Y

. DA L L O U L

DATA MODELING

UNIT 7: DATA MODELINGData Modeling Key Definition

Data Model Logical Data Model Physical Data Model Normalization

Entity Relationship Diagram What Is an ERD? Using the ERD to Show

Business Rules Reading ERD Elements of ERD

Creating an ERD Steps in Building ERDs Add attributes and assign

identifiers Identify relationships

KEY DEFINITIONS

DATA MODEL

A formal way of representing the data that are used and

created by a business system.

Shows the people, places and things about which data is

captured and the relationships among them.

CONCEPTUAL DATA MODEL

Describes WHAT the system

contains

LOGICAL DATA MODEL

Shows the organization of data without indicating how it is

stored, created, or manipulated.

PHYSICAL DATA MODEL

Shows how the data will actually be stored in databases or

files.

NORMALIZATION

It is the process analysts use to validate data

models

ENTITY RELATIONSHIP DIAGRAM

WHAT IS AN ERD

UniversityStudent

PK StudentID

StudentName StudentDOB StudentAge

Entity

Attributes

Primary key

WHAT IS AN ERD

A picture/drawings showing the information created,

stored, and used by a business system.

Entities generally represent similar kinds of information

Lines drawn between entities show relationships among

the data

High level business rules are also shown

USING THE ERD TO SHOW BUSINESS RULES Business rules are constraints that are followed when the

system is in operation.

ERD symbols can show when one instance of an entity

must exist for an instance of another to exist.

A doctor must exist before appointments for the doctor

can be made

EXAMPLE OF ERD

READING ERD

READING ERD

This diagram implement the ERD for a doctor Office

system

Data can be organized into six different categories

(Patients, Appointment, doctors, bill, Payments, and

Insurance company)

The Patient information include patient’s ID number, last

name, first name, address phone number …

READING ERD

Each category has a piece of information used to

uniquely identify it, as examples:

Patient ID number uniquely identify each patient

Bill number uniquely identify each bill

READING ERD

The lines connecting the six categories communicate the

relationships that categories share. So you can

understand that a doctor is scheduled by an appointment

that is scheduled by a patient

READING ERD

ERD is also presents high level business rules. Business

rules are constraints or guidelines that are followed

during the operation of the system.. They are rules like Only one person can be seen by a doctor at a time Payments can be made in the form of cash or check Payment can be paid by insurance, patient, or

combination of both.

READING ERD

On the data model business rule are communicated by

relationships, in example

A patient can schedule by many appointment

A person does not have to be insured to become a

patient

WHAT IS AN ERD ELEMENTS

CREATING AN ERD

Drawing the ERD is an iterative process of trial and

revision

ERDs can become quite complex

STEPS IN BUILDING ERD

Identify the entities

Identify major categories of information

Verify that there is more than one instance of the entity

that occurs in the system


Add attributes and assign identifiers

Identify attributes of the entity that are relevant to the

system under development

Select the entity’s identifier


Identify Relationships

Start with an entity and identify all entities with which it

shares relationships

Describe the relationship with the appropriate verb

phrase

Determine the cardinality and modality by discussing

the business rules with knowledgeable users

ADVANCED SYNTAX

Independent Entity

Is an entity that can exist without the help of another

entity, such as doctor, patient, and insurance company

These entities all have identifiers that were created

using there own attributes

ADVANCED SYNTAX

Dependent Entity

In some situations the child entity does required

attributes from the parent entity to uniquely identify an

instance.

This child entity called dependent entity, such as the

appointment entity, which uses the physicianidnumber

from doctors entity.

ADVANCED SYNTAX

Intersection Entity

It exists in order to capture some information about the

relationship that exists between two other entities.

Typically intersection entity are added to logical data

model to store information about two entities sharing

an many to many relationship

NORMALIZATION

It is a technique helps analysts to validate the model that

they have drawn.

It is a process whereby a series of rules are applied to a

logical data model to determine how well it formed is.

FIRST NORMAL FORM (1NF)

A logical data model in first normal form (1FN) if it not

contains attributes that have repeating values for a single

instance of an entity.

This form should solve repeating attributes and

repeating groups’ problems.

Note the following example of the entity (special orders)


The attribute customer book preferences are a list of

kind of books customers like to read.

As you note there are a repeating attribute which is the

preferences

And there is another repeating group with Books. This

group of (isbn, name, author,publicationyear,

authoruniversity) they all may repeated many times for

each special orders.

SECOND NORMAL FORM (2NF)

In this form, for each entity, the attributes that serve as

identifier can determine the value for all of the other

attributes for an instance in an entity.

In the last example, the special order entity had three

attributes that were used as identifiers (special order

date, customer last name, and customer first name).


These attributes used to identify a customer, but can not

identify the special form attributes such as order status.

To resolve the problem, anew entity called Customer was

created.

THIRD NORMAL FORM (3NF)

Occurs when a model is in both 1NF and 2NF and when

in the resulting entities none of the attributes are

dependent on a non identifier attribute.

In our example this problem with the book entity is that

the author university is dependent on the author.


And in the special order entity Store name, location and

manager are not dependent on special order.

To resolve this problem an entity called author was

created, and another entity called store was created.


Third normal form is also address problem caused by

derived, or calculated, attributes. No need to store

calculated attributes such as the age if we already stored

the birthrate.

In our example, we dropped the attribute days in order

from special order entity because it can be derived from

special order date.

EXERCISES

Whenever new patients are seen for the first time, they complete a patient information form that asks their name, address, phone number, and insurance carries, all of which is stored in the patient information file. Patient can be signed up with only with only carrier, but they must be signed up to be seen by the doctor. Each time a patient visits the doctor, an insurance claim is sent to the carrier for payment. The claim must contain information about the visit. Such as date, purpose, and cost. It would be possible for a patient to submit to claims on the same day.

Draw an entity relationship diagram for the following situations:

EXERCISES

A department store has a bridal registry. This registry keeps information about the customer (usually the bride), the products that the store carries, and the products for which each customer registers. Customer typically registers for the same products.

Draw an entity relationship diagram for the following situations:

SAFAA S.Y. DALLO

UL

S A F A A D A L L O U L . WO R D P R E S S . C

O M

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System analysis and design

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