Page 106 - DCAP305_PRINCIPLES_OF_SOFTWARE_ENGINEERING

Principles of Software Engineering

Notes • The advanced or detailed COCOMO’81 model incorporates all characteristics of the
intermediate version with an assessment of the cost driver’s impact on each step (analysis,
design, etc.) of the software engineering process.
The COCOMO’81 models depends on the two main equations:

1. Development effort: MM = a * KDSI based on MM - man-month / person month / staff-
b
month is one month of effort by one person. In COCOMO’81, there are 152 hours per
Person month. According to organization this values may differ from the standard by 10%
to 20%.

2. Effort and development time (TDEV): TDEV = 2.5 * MM The coefficients a, b and c depend
c
on the mode of the development. There are three modes of development:

Table 5.1: Development Modes

Development Mode Project Characteristics
Size Innovation Deadline/ Dev. Environment
constraints
Organic Small Little Not tight Stable
Semi-datached Medium Medium Medium Medium
Embedded Large Greater Tight Complex hardware/
customer interfaces

The basic COCOMO (COnstructive Cost Model) applies the parameterised equation without
much detailed consideration of project characteristics (See Figure 5.5).

Figure 5.5: Basic COCOMO

Basic COCOMO a b c
MM = a * KDSI b Organic 2.4 1.05 0.38
Semi-deteched 3.0 1.12 0.35
TDEV = 2.5 * MM c Embeded 3.6 1.20 0.32

5.3.1 Intermediate COCOMO
The same basic equation for the model is used, but fifteen cost drivers are rated on a scale of
‘very low’ to ‘very high’ to calculate the specific effort multiplier and each of them returns an
adjustment factor which multiplied yields in the total EAF (Effort Adjustment Factor). The
adjustment factor is 1 for a cost driver that is judged as normal.

In addition to the EAF, the model parameter “a” is slightly different in Intermediate COCOMO
from the basic model. The parameter “b” remains the same in both models (See Figure 5.6).

Figure 5.6: Intermediate COCOMO

Intermediate COCOMO a b c
MM = a * KDSI b Organic 3.2 1.05 0.38
Semi-deteched 3.0 1.12 0.35
TDEV = 2.5 * MM c Embeded 2.8 1.20 0.32

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