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chaPter 7 • Using Data Flow Diagrams 193

Figure 7.13
Customer Number 1 Data flow diagrams for the
and Password first three rows of the Internet
Get Customer Record storefront event response table.
Customer D1 Customer Master
Welcome Web Page Customer
Signin

2
Item Information
Customer Item Response Browse Item Record D2 Item Master
Item
Web Page
Records

Shipping Rates
D8 Shipping Tables

Item Purchased 3 Item Record D2 Item Master
Add
Customer Items Purchased Customer
Web Page Order Detail
Item D7 Order Detail

Customer Record
D1 Customer Master

draw a dashed line around a process or group of processes that should be placed into a single
computer program.
There are six reasons for partitioning data flow diagrams:
1. Different user groups. Are the processes performed by several different user groups, often
at different physical locations in the company? If so, they should be partitioned into differ-
ent computer programs. An example is the need to process customer returns and customer
payments in a department store. Both processes involve obtaining financial information
that is used to adjust customer accounts (subtracting from the amount the customer owes),
but the two processes are performed by different people at different locations. Each group
needs a different screen for recording the particulars of the transaction, either a credit
screen or a payment screen.
2. Timing. It is important to examine the timing of the processes. If two processes execute at
different times, they cannot be grouped into one program. Timing issues may also involve
how much data is presented at one time on a web page. If an ecommerce site has rather
lengthy web pages for ordering items or making an airline reservation, the web pages may
be partitioned into separate programs that format and present the data.
3. Similar tasks. If two processes perform similar tasks, they may be grouped into one com-
puter program.
4. Efficiency. Several processes may be combined into one program for efficient processing.
For example, if a series of reports needs to use the same large input files, producing them
together may save considerable computer run time.
5. Consistency of data. Processes may be combined into one program for consistency of data.
For example, a credit card company may take a “snapshot” and produce a variety of reports
at the same time just so figures are consistent.
6. Security. Processes may be partitioned into different programs for security reasons. A dashed
line may be placed around web pages that are on a secure server to separate them from those