15.2 Personal Software ProcessSM

The benefits of software process improvement (SPI) methods come from increased quality and thus decreased software maintenance and total life cycle costs. That is, most popular SPI methods are specifically designed to increase the quality of the software product. Many popular SPI methods are software quality management systems, because they are designed to improve quality. What strategy will we use for determining the benefits of any one SPI method? We will determine what the software maintenance and total life cycle costs are before and after introduction of the SPI method. That is, first we will determine what the software maintenance and total life cycle costs are before introduction of the SPI method. Then we will determine what the software maintenance and total life cycle costs are after introduction of the SPI method.

The only issue is to determine whether the new and old software maintenance and total life cycle costs include testing costs. That is, does the software organization have a rigorous software testing process? We will assume the software organization does not have a rigorous software testing process, which is most likely the case. Without testing, the software maintenance and total life cycle costs are much higher. Likewise, we can assume the software organization does have a rigorous software testing process, which is probably not the case. With rigorous testing, the software maintenance and total life cycle costs are much lower. Thus, if good software testing is already in place, then the benefits are much lower. If good software testing is not in place, then the benefits are much higher. We will assume a good software testing process is in place, in order to be conservative.

14.1 Software Inspection Process

Let's begin by modeling the costs for analyzing, designing, and developing 10,000 lines of code. Let's further assume our software effort is 5,088 hours to analyze, design, and code 10,000 lines of code.

Let's also begin by estimating the cost of software testing, and assume that good software testing is in place so as to be conservative. Let's assume that we started with 1,000 software defects. Let's further assume that our software testing process nabs two- thirds of our 1,000 defects or 667 software defects. Let's also assume it takes 10 hours to find each of the 667 software defects. That comes to 6,670 software testing hours.

Let's use our total life cycle cost model to determine the cost of developing 10,000 lines of code using software testing. The formula is software size multiplied by 10.51, less the test hours times nine. Our total life cycle cost for using software testing alone is 45,099.97 hours. Multiply 45,099.97 by $100, and the total life cycle cost of using software testing is $4,509,997 to develop 10,000 lines of code.

Now let's use our total life cycle cost model to determine the cost of developing 10,000 lines of code using inspections. The formula is software size multiplied by 10.51, less the inspection hours times 99, and less the test hours times 9. Our total life cycle cost for using the Software Inspection Process is 17,425.33 hours. Multiply 17,425.33 by $100. The total life cycle cost of using the Software Inspection Process is $1,742,533 to develop 10,000 lines of code. Table 8 illustrates the benefits of the Software Inspection Process.

Table 8: Estimated Benefits of Software Inspection Process

State	Total Life Cycle Cost
Before Inspections	$4,509,997
After Inspections	$1,742,533
Benefits	$2,767,464

Now we are ready to estimate the benefits of using the Software Inspection Process to help produce 10,000 lines of code. Subtract $1,742,533 from $4,509,997, which represents total life cycle costs. The benefits of using the Software Inspection Process to help produce 10,000 lines of code are $2,767,464.