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Figure D-13. Common Subsystem modularity D.7.5 Adaptability

Over the entire Common Subsystem, about 5% of the total effort was expended in rework activities against software baselines. The average cost of change was about 24 hours per SCO. These values provide some insight into the ease with which the software baselines could be changed. The level of adaptability achieved by CCPDS-R was roughly four times better than the typical project, in which rework costs over the development life cycle usually exceed 20% of the total cost.

Figure D-14 plots the average cost of change across the Common Subsystem schedule. The 1,600+ SCOs processed against the evolving configuration baseline by FQT resulted in a fairly stable cost of change. CCPDS-R is one of the few counterexamples of "the later you are in the life cycle, the more expensive things are to fix."

Most of the early SCO trends (shown in the box labeled "Design Changes" in Figure D-14) were changes that affected multiple people and multiple components (that is, interface or architectural changes). The later SCO trends (shown in "Implementation Changes") were usually localized to a single person and a single component. The final phase of SCOs reflected an uncharacteristic increase in breakage, the result of a large engineering change proposal that completely changed the input message set to the Common Subsystem. This was one area of the software design that was not as easy to change as we might have hoped. Although the design was very robust and adaptable for numerous premeditated change scenarios, an overhaul of the message set was never foreseen nor accommodated in the design.

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