Information Technology Reference
In-Depth Information
Activity modeling is often accomplished through the use of data-flow diagrams. A
data-flow diagram (DFD)
models objects, associations, and activities by describing how data
can flow between and around various objects. DFDs work on the premise that every activity
involves some communication, transference, or flow that can be described as a data element.
DFDs describe the activities that fulfill a business relationship or accomplish a business task,
not how these activities are to be performed. That is, DFDs show the logical sequence of
associations and activities, not the physical processes. A system modeled with a DFD could
operate manually or could be computer based; if computer based, the system could operate
with a variety of technologies.
DFDs are easy to develop and easily understood by nontechnical people. Data-flow
diagrams use four primary symbols, as illustrated in Figure 12.18b.
•
Data flow.
The
data-flow line
includes arrows that show the direction of data element
movement.
•
Process symbol.
The
process symbol
reveals a function that is performed. Computing
gross pay, entering a sales order, delivering merchandise, and printing a report are
examples of functions that can be represented with a process symbol.
•
Entity symbol.
The
entity symbol
shows either the source or destination of the data
element. An entity can be, for example, a customer who initiates a sales order, an employee
who receives a paycheck, or a manager who receives a financial report.
•
Data store.
A
data store
reveals a storage location for data. A data store is any
computerized or manual data storage location, including magnetic tape, disks, a filing
cabinet, or a desk.
Comparing entity-relationship diagrams with data-flow diagrams provides insight into the
concept of top-down design. Figure 12.18a and b show an entity-relationship diagram and
a data-flow diagram for the same business relationship—namely, a member of a golf club
playing golf. Figure 12.18c provides a brief description of the business relationship for
clarification.
data-flow diagram (DFD)
A model of objects, associations,
and activities that describes how
data can flow between and around
various objects.
data-flow line
Arrows that show the direction of
data element movement.
process symbol
Representation of a function that is
performed.
entity symbol
Representation of either a source or
destination of a data element.
data store
Representation of a storage location
for data.
Application Flowcharts
Application flowcharts
show the relationships among applications or systems. Assume that
a small business has collected data about its order processing, inventory control, invoicing,
and marketing analysis applications. Management is thinking of modifying the inventory
control application. The raw facts collected, however, do not help in determining how the
applications are related to each other and the databases required for each. These relationships
are established through data analysis with an application flowchart (see Figure 12.19). Using
this tool for data analysis makes clear the relationships among the order processing functions.
In the simplified application flowchart in Figure 12.19, you can see that the telephone
order clerk provides important data to the system about items such as versions, quantities,
and prices. The system calculates sales tax and order totals. Any changes made to this order
processing system could affect the company's other systems, such as inventory control and
marketing.
application flowcharts
Diagrams that show relationships
among applications or systems.
Grid Charts
A
grid chart
is a table that shows relationships among various aspects of a systems develop-
ment effort. For example, a grid chart can reveal the databases used by the various applications
(see Figure 12.20).
The simplified grid chart in Figure 12.20 shows that the customer database is used by
the order processing, marketing analysis, and invoicing applications. The inventory database
is used by the order processing, inventory control, and marketing analysis applications. The
supplier database is used by the inventory control application, and the accounts receivable
database is used by the invoicing application. This grid chart shows which applications use
common databases and reveals that, for example, any changes to the inventory control ap-
plication must investigate the inventory and supplier databases.
grid chart
A table that shows relationships
among the various aspects of a
systems development effort.
