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Engineering Systems Integration
Integration as a Recursive Process
Fundamentally, building a product or service is an integrative process;
however, testing is not an integrative process. Planning for integration should
be based on developing system-level functions that are in-kind built up by
their subfunctions. The first step is to focus on those subfunctions that when
linked together with other subfunctions form an end-to-end thread that
stretches across the entire system. That end-to-end threat is referred to as a
system-level thread (or “thread”). Each time a subfunction is linked to
another subfunction (recall each function is the result of the integration of
two objects), the performance and quality of the linked subfunctions are
measured. Measures of performance and measures of quality are stipulated
as part of the test plan. The integration plan identifies the objects that are
to be linked together to provide the subfunctionality necessary to constitute
a thread.
Measures of Integration
The measures of quality are premised on two factors: quality is the achievement of a level of acceptable variability of each measure of performance, and
the variability in performance is representative of the user’s perception of
quality. For example, a vehicle is said to be moving at 60 km/h (a measure
of the vehicle’s performance). The accuracy of the measurement (its bias due
to systematic errors) is 0.003% of the measured performance; the precision of
the measurement (its uncertainty due to random errors) is 0.0002% of the
measured performance. The manufacturer of the vehicle offers an automatic
speed control device as an accessory. The variance (the spread of the measurements for both accuracy and precision) matches a Gaussian distribution.
Based on the customer’s (user’s) requirements, the manufacturer will customize the speed control device by setting its upper and lower limits. When
the vehicle speed is less than the lower limit or greater than the upper limit,
the speed controller will adjust the speed of the vehicle whether moving on
an incline (positive or negative slope) or on level ground. Assuming that the
precision and accuracy are measurably the same, the adjustment of the upper
and lower limit of performance is now only determined by the customer’s
willingness to pay the price asked for by the manufacturer. The smaller the
variance (i.e., the closer the lower and upper limits are to each other) around
the target value for the vehicle’s speed, the higher the price. However, the
price is not a linear function of the distance between the upper and lower
limits. As the distance between these limits approaches the exact target
value for the vehicle’s speed, the cost is significantly higher than near the