Transcript chap3 seq9.ppt

System Analysis and Design
System Analysis
- Mr. Ahmad Al-Ghoul
Learning Objectives



Discuss how to create a set of
data flow diagrams in a sequence,
from general to specific
discuss and draw the context
diagram
Discuss and draw a Diagram 0
Avicenna
System Analysis and Design
System Analysis
2
Creating a Set of DFDs


Create a graphical model of the information
system based on your fact-finding results
Create a set of DFDs by performing three main
tasks


Step 1: Draw a context diagram, including all
external entities and the major data flow to or from
them
Step 2: Draw a diagram 0 DFD by analyzing the major
activities within the context process


Avicenna
Include the external entities and major data stores
Step 3: Draw the lower-level diagrams for each
complex process on Diagram 0
System Analysis and Design
System Analysis
3
Creating a Set of DFDs

The procedure for producing a DFD is to:









Avicenna
identify and list external entities providing inputs to the system
and receiving outputs from system
identify and list inputs from external entities and outputs to
external entities
create a context diagram with system at center and external
entities sending and receiving data flows
identify the processes included within the system boundary
identify the data connections between processes
verify all data flows have a source and destination
verify data coming out of a data store goes as input to a process
review with "informed"
explode and repeat above steps as needed
System Analysis and Design
System Analysis
4
Creating a Set of DFDs

Draw a Context Diagram







Avicenna
Context Diagram is going to be the simplest DFD ( will have the
minimum amount of symbols)
First DFD in every business process
Shows the context into which the business process fits
Contains only one process, representing the entire system
The process is given the number zero
All external entities are shown on the context diagram as well as
major data flow to and from them
The diagram does not contain any data stores
System Analysis and Design
System Analysis
5
Creating a Set of DFDs

Draw a Context Diagram


Avicenna
Begin by reviewing the system requirements
to identify all external data sources and
destinations
Record the name of the entities and the name
and content of the data flows, and the
direction of the data flows
System Analysis and Design
System Analysis
6
Creating a Set of DFDs

We will use example of information system, the example is an
order system that a company uses to enter orders and apply
payments against a customer's balance

External entities are






Order information system consist of three main processes



Avicenna
CUSTOMER
WAREHOUSE
SALES REP
BANK
ACCOUNTING
FILL ORDER: which contains three sub processes, VERIFY ORDER,
PREPARE REJECT NOTICE, and ASSEMBLE ORDER
CREATE INVOICE: no sub process
APPLY PAYMENT: which contains four sub processes POST
PAYMENT, DEPOSIT PAYMENT, PREPARE ACCOUNTING ENTRY, and
PAY COMMISSION
System Analysis and Design
System Analysis
7
Creating a Set of DFDs
Context diagram DFD for an order system.
 Notice that the ORDER SYSTEM process is at the
center of diagram and five entities surround the
process
 Three of the entities, SALES REP, BANK, and
ACCOUNTING, have a single incoming data flows
for COMMISSION, BANK DEPOSIT, and CASH
RECEEIPTS
 The WAREHOUSE entity has one incoming data
flow PICKING LIST that is a report, that shows the
items and their quantity, location, and sequence.
The WAREHOUSE entity has one outgoing data
flow, COMPLETED ORDER
 The CUSTMER entity has two outgoing data flows,
ORDER and PAYMENT, and two incoming data
flows, ORDER REJECT NOTICE and INVOICE [1]
Avicenna
System Analysis and Design
System Analysis
8
Creating a Set of DFDs

Draw a Diagram 0 DFD




Avicenna
The Context Diagram is a good starting point but it does not tell
us much about the system, and that is where low level DFDs
come into play.
In Context Diagram we had only one Process, we will break up
this process into sub-processes.
The Diagram that will result from this breaking-up is called
Diagram 0 (named so, because we are drawing a DFD that
further explains the Process number "0").
How many sub-processes should we make out of Process 0?
There is no rule It all depends on the system
System Analysis and Design
System Analysis
9
Creating a Set of DFDs

Draw a Diagram 0 DFD








Avicenna
Diagram 0 is the explosion of the context level diagram
Processes are numbered with an integer
The process numbers do not suggest that the processes are
accomplished in a sequential order
Each process always is considered to be available, active, and awaiting
data to be processed
The major data stores and all external entities are included on Diagram
0
A diverging data flow is a data flow in which the same data travels to
two or more different locations
If same data flows in both directions, you can use a double-headed
arrow
To identify specific data flows into and out of a symbol, however, you
use separate data flows symbols with single arrowheads
System Analysis and Design
System Analysis
10
Creating a Set of DFDs

Draw a Diagram 0 DFD


If more detail were needed for any process in diagram 0, you
would draw a level 1 diagrams
If more detail needed for any process in level 1 diagrams , you
would draw a level 2 diagrams, and so on

Parent diagram


Child diagram



Avicenna
The lower level diagram
Functional primitive


The higher level diagram
Processes that do not create a child diagram
You document the logic for a functional primitive in a process
description in the data dictionary
Later, when the logical design is implemented as a physical system,
programmers will transform each functional primitive into a unit of
program code that carries out the required processing steps.
System Analysis and Design
System Analysis
11
Creating a Set of DFDs
diagram 0 for an order system.
Notice that process 0 on the order system’s context
diagram is exploded to show three processes, FILL
ORDER, CREATE INVOICE, and APPLY PAYMENT
one data store, ACCOUNTS RECEIVABLE
two new data flows, INVOICE DETAIL and PAYMENT
DETAIL
One diverging data flow INVOICE

Depending on the processing logic

A CUSTOMER submit an ORDER, the FILL ORDER
process either sends ORDER REJECT NOTICE to the
customer entity or sends PICKING LIST to the
WAREHOUSE entity

A COMPLETED ORDER from the WAREHOUSE entity is
input to the CREATE INVOICE process, which output
INVOICE to both CUSTOMER entity and the
ACCOUNTS RECEIVABLE data store

PAYMENT processed by APPLY PAYMENT process
requires INVOICE DETAIL from ACCOUNTS
RECEIVABLE data store a long with the PAYMENT.
APPLY PAYMENT process outputs PAYMENT DETAIL to
the ACCOUNTS RECEIVABLE data store and outputs
COMMISSION to the SALES DEPT entity, BANK
DEPOSIT to the BANK entity, and CASH REEIPTS
ENTRY to ACCOUNTING entity
Avicenna
System Analysis and Design
System Analysis
[1]
12
Creating a Set of DFDs

Drawing Guidelines
1.
2.
3.
4.
5.
6.
Avicenna
Draw the context diagram so that it fits on one page
Use the name of the information system as the
process name in the context diagram
Use unique names within each set of symbols
Do not cross lines
Provide a unique name and reference number for
each process
Obtain user input and feedback
System Analysis and Design
System Analysis
13
Sequence Summary



A set of DFDs is like a pyramid with the
context diagram at the top
The context diagram represents the information
system’s scope and its external connections but
not its internal working
Diagram 0 displays the information system’s
major processes, data stores, and data flows
and its exploded version of the context
diagram’s process symbol, which represents the
entire information system
Avicenna
System Analysis and Design
System Analysis
14
Sequence Summary

In this Sequence we have

Discuss how to create a set of data flow
diagrams in a sequence, from general to
specific
explained the context diagram
Explained the steps needed to draw the
context diagram
Explained a Diagram 0

Explained how to draw a diagram 0



Avicenna
System Analysis and Design
System Analysis
15
Reference
[1] System Analysis and Design, Sixth Edition
Authors: Gary B. Shelly, Thomas J. Cashman and Harry J. Rosenblatt ,
Publisher: SHELLY CASHMAN SEWIES.
[2] system analysis and design, sixth edition
Authors: Kenneth E. Kendall and Julie E. Kendall
Publisher: Prentice Hall
[3] Modern Systems Analysis and Design Third Edition
Authors: Jeffrey A. Hoffer , Joey F. George, Joseph S. Valacich
Publisher: prentice hall
[4] System Analysis and Design, 3rd Edition
Authors: Dennis, Wixom, & Roth
Publisher: John Wiley & sons
Avicenna
System Analysis and Design
System Analysis
16