El-Shorouk Academy
Acad. Year
: 2011 / 2012
Higher Institute for Computer &
Term
: Second
Year
: Second
Information Technology
Department of Computer Science
Systems Analysis
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 diagram
2. Level -0 diagram
3. Level 1 , 2,3,………,n ( detailed levels or child diagrams)
Context
Level
level ᴓ
DFD
Level 1
level 2
level ....N
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 :
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
system
EX: Inventory reporting subsystem
- In the detailed levels ( level 1 , level 2 ,…..) we follow the role:
Verb – adjective – noun
EX: 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:
Name
 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 entities
Level-ᴓ contain external entities
Level 1 , 2 ,3,..  doesn’t contain external entities
 Data Flow:
Name
 Data flowing in the system
 Data store:
No
name of 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
0
Customer
Order
Invoice
XYZ
2- Level -0 diagram
1
2
Order
Invoice
Processed Order
Sales
Accounting
Invoice
Invoice
Status Enquiry
3
Store
Invoice
2
Invoice + items
1
Archive
Archive
3- detailed levels
-
level 1
1.1
Order
Receive
Customer
Order
1.2
Order
Verify Order
Items
Invoice
Processed Order
Invoice
Invoice
1.3
1.4
Receive
Invoice
Enquiry Order
items
Enquiry
Status
Processed Order
1.5
Sending
Processed Order
Processed Order
Invoice
- Level 2
2.1
Processed Order
2.2
Receive
processed
Order
Processed Order
Generate
Invoice
Invoice
2.3
Sending
Invoice
-
Invoice
level 3
3.1
Enquiry
Receiving
enquiry item
3.2
Status
Invoice
Receive
Invoice
Invoice + items