Information Technology Reference
In-Depth Information
Customer Usage
Coupling
Test/
Debug
Obsolescence
Useful Life
λ
Upgrades
Time
FIGURE 18.5
The effect of noise factors during the software life cycle.
6
Parameter design is the most used phase in the robust design method. The objective
is to design a solution entity by making the functional requirement insensitive to the
variation. This is accomplished by selecting the optimal levels of design parameters
based on testing and using an optimization criterion. Parameter design optimization
criteria include both quality loss function and SN. The optimum levels of the
x's
or
the design parameters are the levels that maximize the SN and are determined in an
experimental setup from a pool of economic alternatives. These alternatives assume
the testing levels in search for the optimum.
Several robust design concepts are presented as they apply to software and product
development in general. We discuss them in the following sections.
18.3
ROBUST DESIGN CONCEPT #1: OUTPUT CLASSIFICATION
An output response of software can be classified as static or dynamic from a robustness
perspective. A static entity has a fixed target value. The parameter design phase in
the case of the static solution entity is to bring the
response (y)
mean,
µ
y
,tothe
target,
T
y
. For example, we may want to maximize the quality of programmer ability
or streamlining software debugging. However, the dynamic response expresses a
variable target depending on the customer intent. In this case, the DFSS optimization
phase is carried across a range of the useful customer applications, called the signal
factor. The signal factor can be used to set the
y
to an intended value.
Parameter design optimization requires the classification of the output re-
sponses (depending on the mapping of interest in the context of Figure 13.1) as
smaller-the-better
(e.g., minimize coding man-hour),
larger-the-better
(e.g., increase
6
Modified graph. The original can be found at http://www.ece.cmu.edu/
∼
koopman/des s99/sw reliability/
presentation.pdf.
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