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have special purpose to work and make proper decisions. System designers who
are working on a group-based system should have a workable global based system
already in place. The design focus is generally on output, input, process, and
control which pertain to a specific group (Burch 1992 ).
7.1.3 Local-Based Systems
A local-based system is typically designed for few people, or for an ad hoc
application. A systems professional is generally called into work with the user in
analyzing and designing requirements, evaluating different systems, acquiring one,
and implementing it, along with network and support. Another example is an
executive information system developed for decision makers (Burch 1992 ).
7.2 Function-Oriented Approach
A function-oriented design strategy relies on decomposing the system into a set of
interacting functions with a centralized system state shared by these functions.
Functions may also maintain local state information, but only for the duration of
their execution. Function-oriented design has been practiced informally since
programming began. Programs were decomposed into subroutines which were
functional in nature. In the late 1960s and early 1970s several topics were pub-
lished which described 'top-down' functional design. Function-oriented design
conceals the details of an algorithm in a function, but system state information is
not hidden. This can cause problems because a function can change the state in a
way which other functions do not expect. Changes to a function and the way in
which it uses the system state may cause unanticipated changes in the behavior of
other functions. A functional approach to design is therefore most likely to be
successful when the amount of system state information is minimized and infor-
mation sharing is explicit.
Systems whose responses depend on a single stimulus or input and which are
not affected by input histories are naturally functionally-oriented. Many transac-
tion-processing systems and business data-processing systems fall into this class.
In essence, they are concerned with record processing where the processing of one
record is not dependent on any previous processing. An example of such a
transaction processing system is the software which controls automatic teller
machines (ATMs) which are now installed outside many banks. The service
provided to a user is independent of previous services provided so it can be thought
of as a single transaction (Sommerville 1996 ). Figure 7.2 shows the design view of
the function-oriented approach.
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