Part III: The Analysis Process
Lecture Note 8
Using Data Flow Diagrams
Systems Analysis and Design
Kendall & Kendall
Sixth Edition
Major Topics
• A Data Flow Diagram Example for Video
Rental System of FilmMagic Co.
• The Second Data Flow Diagram Example
for Order Processing System of World’s
Trent Co.
CS206 Syatem Analysis & Design
Note 8 By ChangYu
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A Data Flow Diagram
Example
• The corporation in our
example is FilmMagic, a video
rental chain founded by the
three people with expertise in
the video rental business.
• A summary of the business
activities are obtained from
interviewing with the owners of
FilmMagic.
• Start with a list of business
activities, which will help you
identify Processes, External
Entities, Data flow and Data
Stores.
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1.
Apply a video rental card:
a)
b)
2.
Make a List
Rent DVDs with video rental card:
a)
b)
c)
d)
e)
3.
Customers apply for a video rental
card. They fill out a form and
provide a means of verifying their
identity.
They are issued a video rental
cad.
Customers rent videos by giving
the clerk their video rental card
and the DVDs or video games.
The clerk totals the amount of the
rental, which is received from the
customers.
Customers are given a receipt with
the due date on it.
A record is created for each item
rented.
The video rent card is returned to
customer.
Return :
a)
b)
Customers return DVDs or video
games.
If the item is returned late, a note
and the amount of the late fee is
made on the record.
What information is
needed to rent a DVD?
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4. If a customer has a late fee, he or she is required to pay the amount the
next time an item is rented.
5. The company has several special
policies designed to provide a
competitive edge in the video
rental market. Once a month, the
customer rental records are
reviewed for customers who have
rented more than the bonus level,
currently set at $50. Bonus
customers are sent a letter
thanking them for their business
as will as issuing them several
free rental coupons (depending on
the amount of rental for the
month).
6. Once a year, the customer records are examined for customers who have
rented more than a yearly bonus level (currently set at $250). A letter, free rental
coupons, and a certificate for a free video (if a customer has rented over two
times the bonus level) are sent to the customer.
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Creating the Context Diagram
External Entity:
• Video Purchase System
-- Provide information
about Video item.
• Management – needs
management reports to
managing and making
decision.
• Accounting – accept
total cash.
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Drawing
Diagram 0
Diagram 0 for the
FilmMagic video rental
system shows seven
major processes. This
logical DFD tell us
Rent
video
Handle new
customers case
• What the system does,
• What is stored,
• Who or What provides
the inputs, and
Update
customer
data store
• Who receives the
output.
Useful information for
managing the business and
making decisions.
Use customer data store to produce
monthly or yearly bonus letter.
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Creating a Child Diagram
Child Diagram: Diagram 1:
• Get video record: uses DVD
the customer wishes to rent to
find matching title, price and so
on.
• Find Customer Record: use
customers ID on the video rent
card to locate the customer
record, so as to get the
customer’s name and address.
• Produce Customer
Receipt :
rental receipt should be included
customer’ information and rental
information.
• Get Customer Payment:
produce a cash transaction.
• Update Customer Record
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Creating a Physical Data Flow Diagram
This physical data flow
diagram corresponds to logical
Diagram 0. note the subtle
differences.
CUSTOMER ID is now CUSTOMER ID
BAR CODE, emphasizing physical
implementation.
The Entity Video Purchase System has
been replaced with a Video Master File
because the file is used to communicate
between systems.
Is necessary because videos are rented
throughout the day, but the cash received
report is produced only once a week.
Is used to store information from the time
the videos are rented until they are
returned.
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Physical Child DFD
This physical child data flow
diagram shows details about real
world implementation. The logical
diagram process 1.1 was GET
VIDEO RECORD, but the physical
diagram process 1.1 tell us how
SCAN VIDEO BAR CODE.
Notice that there are processes
for scanning bar codes,
displaying screens, locating
records and creating and
updating files. The sequence
of activities is important here,
because the emphasis in on
how the system will work and
in what order events happen.
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Partitioning the DFD
Partitioning takes the physical
DFD and makes programming and
implementation manageable.
Notice the use of dotted lines to indicate which
processes should be in separate programs.
• The process 1 and process 3 operates on a
minute-by-minute basis. Returns, are handle at
a time later than the rental process, and both
procedures should thus be in separate program.
• The process 2 is weekly and must be in a
separate program. Cash Transaction Record and
Cash Received Report are both computer
information, the process should be implemented
as a batch program.
• The process 4, 6 and 7 should be
implemented as a batch program.
• The process 5 could be either batch or online.
Because the customer is probably waiting for
the video Rental card on the other side of a
counter, an online process would provide the
best customer server.
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The Second Data Flow
Diagram Example
A summary of business activities for
World’s Trent Catalog Division.
• World’s Trend is a mail-order supplier of high-quality,
fashionable clothing. Customers place orders by telephone,
faxing, mailing an order form included with each catalog, or
via the web site.
• You develop this list using information obtained through
interviews, investigation and observation.
• The list can be used to identify External Entities as well as
some Data Flows, Data Stores and Processes.
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1.
2.
3.
Add new customers to the
Customer Master File. When
customers are added to the
master file, they are assigned a
Customer-Number, which is
used when placing subsequent
orders.
Perform inquires to let
customers know the current
selling price of an item and the
quantity available for sale.
Process customer orders by
Verifying that all order
information is accurate and that
a record exists for the customer
placing the order. If a customer
record does not exist, it is added
to the master’s file. As orders are
entered, customer and item
Master Record Fields are
updated.
List of Business Activities
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4. If a customer orders more of an item
5.
6.
7.
8.
than is currently available in stock,
back-ordered item information is
sent to the inventory control
department. When back-ordered
items are received form World’s
Trend suppliers, they are shipped
to the customers.
Orders are sent to the warehouse
where they are filled.
A shipping statement is attached to
the filled order. Mailing labels are
prepared, and the order is shipped
to the customer.
Order information is used to produce a
billing statement for all customers
charging their goods to their
World’s Trend account.
Order information is used to produce
an accounts receivable report for
the accounting department.
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Creating the Context Diagram
External
entities:
• Inventory
Control
Department
• Accounting
Department
• Warehouse
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Diagram 0
Order Processing System
has some sub-processes:
• Add Customer Order
• Add Customer Record
• Produce Picking Slips
• Prepare Shipping Statement
• Ship Customer Order
• Create Customer Statement
• Produce Accounts Receivable
Data Stores:
• Item Master
• Customer Master
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Diagram 1
How to Add Customer Order:
• Validate Customer Account
• Validate Order Item
• Determine Quantity Available
• Update Item Quantity
• Calculate Order Totals
• Update Customer Record
• Create Pending Order
Data Stores:
• Customer Master
• Shipping and Handling Table
• Item Master
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The Physical Data
Flow Child Diagram
Produce Picking Slips:
When you label a physical model,
take care to describe the process in
great detail.
• Sub-process 3.3 in local model could
simply be SORT ORDER ITEM , but
in physical model, a better label is
SORT ORDER ITEM BY LOCATION
WITHIN CUSTOMER.
• When you write a label for a data
store, refer to the actual file or
database, such as CUSTOMER
MASTER FILE, SORTED ORDER
ITEM FILE, ITEM ORDER FILE
AND ORDER ITEM FILE.
• When you describe data flows,
describe actual form, report or screen.
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Partitioning the
DFD
Finally, take the physical
data flow diagram and
suggest partitioning
through combining or
separating the processes.
• You must group processes
1 and 2, because it would
make sense to add new
customers at the same time
their first order was placed.
• You would then put
processes 3 and 4 in two
separate partitions.
Although both are batch
processes, they must done
at different times from each
other and thus cannot be
grouped into a single
program.
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Review Questions
• What is a data flow diagram?
• What is advantages of the Data Flow Diagram
Approach?
• What are the steps of developing Data Flow
Diagrams ?
• What is the different between logical DFD and
physical DFD?
• What are the reasons for Partitioning?
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