S CxKxtd

Total lifetime effort B = (1/T4) (200,000/4,000)3 = (1/T4) (50)3

Development effort E = 0.3945 B

If target development period is two years, then

Total lifetime effort B = (1/16) (50)3 = 7,812.5 staff-years

Development effort E = 0.3945 B = 3,082 staff-years

Putnam's recommended figures for C for different types of projects are:

• Real-time embedded—1,500; ® Batch development—4,894; ® Supported and organized—10,040;

Effort and productivity change when development time varies between two and three years:

T

E

B

2

3,082

7,814

2.5

1,262

3,200

3

609

1,543

Focusing on the productivity level is one major difference between the Boehm and Putnam models. It can be calculated based on the size, time, and effort values from previously completed projects. Putnam combines attributes of both the process and the product in his definition of productivity, and he separates the wide range of productivity values into an index ranging from 0 to 40. He calls this the process productivity index (PI), based on product attributes such as algorithm complexity and process attributes such as standards and team capabilities. Putnam is careful to explain that the PI is not a fair quantification of personal productivity because some of the attributes may not be within the control of the development team.

The PI makes a huge difference in the effort, schedule, and cost of a project. Organizations can improve their PI, just as they can improve their SEI CMM maturity level. Application types exhibit different Pis. For example, business systems average 17.3, scientific systems average 14.8, telecommunications average 11.4, real-time systems average 8.3, and microcode systems average 6.3.

Size and productivity are constants, while time and effort can be adjusted to some degree. According to Fred Brooks (Brooks' Law), adding people to a late project usually only makes it later. There is a minimum time solution and a minimum effort/cost solution.

Basic steps in estimating with the mathematical model are made palatable with the use of automated tools: Step 1. Estimate software size.

Application of a beta distribution is one way to do this (or expert opinion, analogy, Wideband Delphi).

Sn = the predicted nominal size of the software product Smin = the minimum possible size Si = the most likely size (50% probable) Smax = the maximum possible size Step 2. Determine productivity and environmental factors (PI, C). Step 3. Identify the development constraints (maximum cost, etc.).

Step 4. Construct a planning zone (feasible region versus the impractical or impossible zones) similar to Figure 11-15.

Figure 11-15. Planning Zone

Figure 11-15. Planning Zone

Step 5. Find an acceptable planning point.

The QSM model default is based on four phases (users may customize this): requirements, design, code, and integration. The third phase is determined by estimated size and PI; phases 1 and 2 are determined as percentages of phase 3 values by analysis of historical data; and phase 4 is an extrapolation of the phase 3 staffing curve. (See Figure 11-16.)

Figure 11-16. Staffing Profile

Figure 11-16. Staffing Profile

Jan Apr Jul Oct Jan Apr Jul '99 SQ0

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Project Management Made Easy

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