Box Basic Cocomo Productivity Estimate

Productivity: P = Size Effort

Basic COCOMO Examples

This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks Two examples of basic COCOMO follow. One is simple, and the other is of medium complexity.

Basic COCOMO Example 1

A development project is sized at 7.5 KLOC and is evaluated as being simple—in the organic mode. The basic COCOMO equation for effort (E) in staff-months (SM) is:

Effort (SM) = 2.4(KLOC)1 05 = 2.4(7.5)1 05 = 2.4(8.49296) = 20 staff-months

Development time (TDEV) can also be found by using the basic COCOMO formulas:

TDEV = 2.5(SM)° 38 = 2.5(20)° 38 = 2.5(3.1217) = 8 months

The average number of staff members (S):

Staff = Effort TDEV = 20 staff-months 8 months = 2.5 staff members on average

The productivity rate (P):

Productivity = Size Effort = 7,500 LOC 20 staff-months = 375 LOC/staff-month Basic COCOMO Example 2

A development project is estimated to be about 55 KLOC when complete and is believed to be of medium complexity. It will be a Web-enabled system with a robust back-end database. It is assumed to be in the semidetached mode.

For a rough estimate of the effort that will be required to complete the project, use the formula: E (effort in staff-months) = 3.0(KLOC)1 12

E (effort in staff-months) = 3.0(55)1 12 E = 3.0(88.96) E = 267 staff-months To determine how long it will take to complete the project, use the formula: TDEV = 2.5 x (E)° 35 TDEV = 2.5 x (267)° 35 TDEV = 2.5(7.07) TDEV = 17.67 months

To obtain a rough estimate of how many developers will be needed, use the formula:

S (average staff) = effort-TDEV

To determine a rough estimate of the productivity rate, use the formula:

P (productivity) = size-effort

P (productivity) = 55,000-267

P (productivity) = 206 LOC/staff-month

Basic COCOMO offers a way to calculate a set of quick estimates for effort, development time, staffing, and productivity rates, given knowledge only of size and mode. It can be arrived at with no more than a calculator. However, you get what you pay for. It doesn't take much to derive effort using the basic level, and the results won't be worth much more than a very, very rough estimate. To refine the estimation process, Boehm gives guidance in "tuning" via what he calls a complexity adjustment factor described in intermediate COCOMO.

Basic COCOMO Phase Distribution of Effort and Schedule

In addition to estimating development effort and schedule, it is often necessary to estimate how the effort is distributed among the primary life cycle activities. COCOMO takes a pretty simplistic view of the life cycle phases, considering only plans and requirements, product design, coding, and integration and test as the four development phases, and maintenance as the final life cycle phase. Any of these activities may be going on during any of the phases: requirements analysis, product design, coding, test planning, verification and validation, project office functions, configuration management and quality assurance, documentation, and so on.

Let's look at an example of phase distribution of effort and schedule (see Table 11-3).

Suppose that an embedded mode project is sized at 80 KLOC.

E (effort in staff-months) = 3.6(KLOC)1 20 = 3.6(80)1 20 = 3.6(192.18) = 692 staff-months

TDEV (development time) = 2.5(E)0 32 = 2.5(692)° 32 = 2.5(8.106) = 20 months

Table 11-3. Basic COCOMO Phase Distribution of Effort and Schedule Example, Where Estimated SM = 692 and Estimated

Table 11-3. Basic COCOMO Phase Distribution of Effort and Schedule Example, Where Estimated SM = 692 and Estimated

Plans and Requirements

Product Design

Coding

Integration and Test

Total

Effort (%) (% of effort spent in each major phase, based on historical data)

10%

12%

50.5%

27.5%

100% effort spread over four major phases

Effort (SM) = typical % of effort spent in this phase x estimated SM

.1 x 692 SM = 6.92 months

.12 x 692 SM = 83.04 months

.505x 692 SM = 349.46 months

.275 x 692 SM = 190.3 months

692 months total staff-months

Schedule (%) (% of schedule spent on each major phase, based on historical data)

4%

33%

38%

25%

100% schedule spread over four major phases

Schedule (Months) = typical % of schedule spent on this phase x estimated TDEV

.04x20 = .8 months

.33x 20 = 6.6 months

.38x 20 = 7.6 months

.25x20 = 5 months

20 months duration (schedule)

Average # Personnel per major phase (Effort [SM]/Schedule [Months])

6.92-,8 = 8.65 average persons

83.04-6.6 = 12.5818 average persons

349.46-7.6 = 45.98 average persons

190.3-5 = 38.06 average persons

692-20 = 34.6 average persons

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