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534 Part Four Building and Managing Systems

university’s student master file with information about new students or changes
in address. Process 3.0 then sends each student applicant a confirmation-of-reg-
istration letter listing the courses for which he or she is registered and noting
the course selections that could not be fulfilled.
The diagrams can be used to depict higher-level processes as well as lower-
level details. Through leveled data flow diagrams, a complex process can be
broken down into successive levels of detail. An entire system can be divided
into subsystems with a high-level data flow diagram. Each subsystem, in turn,
can be divided into additional subsystems with second-level data flow diagrams,
and the lower-level subsystems can be broken down again until the lowest level
of detail has been reached.
Another tool for structured analysis is a data dictionary, which contains
information about individual pieces of data and data groupings within a system
(see Chapter 6). The data dictionary defines the contents of data flows and data
stores so that systems builders understand exactly what pieces of data they con-
tain. Process specifications describe the transformation occurring within the
lowest level of the data flow diagrams. They express the logic for each process.
In structured methodology, software design is modeled using hierarchical
structure charts. The structure chart is a top-down chart, showing each level
of design, its relationship to other levels, and its place in the overall design
structure. The design first considers the main function of a program or system,
then breaks this function into subfunctions, and decomposes each subfunction
until the lowest level of detail has been reached. Figure 13.7 shows a high-level
structure chart for a payroll system. If a design has too many levels to fit onto
one structure chart, it can be broken down further on more detailed structure
charts. A structure chart may document one program, one system (a set of pro-
grams), or part of one program.

Object-Oriented Development
Structured methods are useful for modeling processes, but do not handle the
modeling of data well. They also treat data and processes as logically separate
entities, whereas in the real world such separation seems unnatural. Different
modeling conventions are used for analysis (the data flow diagram) and for
design (the structure chart).
Object-oriented development addresses these issues. Object-oriented
development uses the object as the basic unit of systems analysis and design.

FIGURE 13.7 HIGH-LEVEL STRUCTURE CHART FOR A PAYROLL SYSTEM

This structure chart shows the highest or most abstract level of design for a payroll system, providing an overview of the
entire system.

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