El-Shorouk Academy Acad. Year : 2016 / 2017

Higher Institute for Computer & Term : Second

Information Technology Year : Second

Department of Computer Science

Systems Analysis

Section (7)

System modeling

1- Data Flow diagram ( DFD ).

2- Data dictionary ( DD ).

System modeling provides the following advantage:

Provide further understanding to the system from business perspective

Provide a comprehensive documentation to the system Provide away of uniquely define the system components and

elements Can be used as a tool to interact with the system

DFDs includes three levels , naming:

1. Context level diagram2. Level -0 diagram3. Level 1 , 2,3,………,n ( detailed levels or child diagrams)

1- Context level:

Which shows the system very global as one process together with the external entities

Consists of only one process and describe the overall system very global External entity symbol can be used more than one for simplification of the

diagram Context level take the number ᴓ Context level does not contain any data store

A data flow diagram ( DFD ) of the scope of an organizational system that shows that system boundaries , external entities that interact with the system and the major information flows between the entities and the system

Such as that example :

Context Level

level ᴓ DFD

Level 1 level 2 level ....N

2- Level ᴓ diagram:

which represent the breakdown of the previous process but still in general

A more detailed diagram than the context , and obtained by exploding the context – level process

Inputs and outputs exist in the context-level should still appear in the levelᴓ

It can contain from 3-9 processes It can contain , if needed , more inputs and outputs It contain data stores Each process in levelᴓ has a unique sequence number starting from 1

A data flow diagram ( DFD ) that represents a system’s major processes , data flows and data stores at a high level of detail.

Such as example:

3- Detailed levels ( child DFD ):

Which are the breakdown of the previous process but still in general They details the activities of the system by exploding each process in

levelᴓ into its detailed processes Each detailed diagram is down in a separate sheet , and has the

inputs and outputs linked with the above process

Such as Example:

Symbols used in drawing DFD:

Process

#

Process name

A process symbol , with a unique number and a process name Transforming incoming data into outgoing information

Process naming Rules:

- In the Context Level , the overall system process takes the system name ( it is the name of the system)

Ex : Inventory control system

- In the levelᴓ , the processes take the name of the subsystem in the overall systemEX: Inventory reporting subsystem

- In the detailed levels ( level 1 , level 2 ,…..) we follow the role:Verb – adjective – nounEX: compute Sales Tax Verify customer account Prepare shipping invoice A process transform incoming data into out coming information A process can have one or more than , one input and more than one

output

External Entity:

Represent any entity that supply or receive information from the system , but they are not part from the system.

A person , organization , or system that is external to the system but interacts with it

Context level - contain external entitiesLevel-ᴓ contain external entitiesLevel 1 , 2 ,3,.. doesn’t contain external entities

Data Flow:

Data flowing in the system

Data store:

Context level doesn’t contain data store Level-0 contain data store Detailed levels contain data store

Example:

An XYZ organization has 3 departments :

1- Sales dept rolls:- Receive orders from customers- Verify order items- Enquiry about the order items existence from store dept and receive

the status- Send the processed order to the Account dept - Receive the invoice from the accounting department- Send the invoice to the customers

2- Account dept roles:- Receive processed orders from sales dept- Generate the invoice

- Send the invoice to : sales dept, store dept , and to customer

3- Store dept roles:- Receive an enquiry about item existence in the store and reply with

the status- Receive the invoice from Accounting dept to ship the order to

customer

ANSWER

1- Context Level

2- Level -0 diagram

3- detailed levels

- level 1

- Level 2

- level 3