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COCOMO
Short answer
COCOMO is an algorithmic cost estimation model that computes effort, development time, and staffing from software size in KLOC and project mode. For a 50 KLOC organic project, using formulas E=2.4×KLOC^1.05 and D=2.5×E^0.38, effort is about 146 person-months, time 16.6 months, needing about 9 people.
Explain COCOMO.
COCOMO (Constructive Cost Model) is an algorithmic software cost estimation model developed by Barry Boehm (1981). It estimates effort (person-months), development time (months) and staffing from the size of the software in thousands of delivered source lines (KLOC). It is a parametric estimating technique.
Models
- Basic COCOMO: estimates from size only.
- Intermediate COCOMO: adds 15 cost drivers (product, hardware, personnel, project attributes) as an effort adjustment factor (EAF).
- Detailed COCOMO: applies drivers by phase.
Project modes (Basic COCOMO)
| Mode | Description | a | b | c | d |
|---|---|---|---|---|---|
| Organic | Small team, familiar problem, simple | 2.4 | 1.05 | 2.5 | 0.38 |
| Semi-detached | Medium team, mixed experience | 3.0 | 1.12 | 2.5 | 0.35 |
| Embedded | Tight constraints, hardware-dependent | 3.6 | 1.20 | 2.5 | 0.32 |
Formulas
- Effort E = a × (KLOC)ᵇ person-months
- Development time D = c × Eᵈ months
- Average staff = E / D persons
(Intermediate: E = a × (KLOC)ᵇ × EAF, with a = 3.2, 3.0, 2.8 for the three modes.)
Worked example: 50 KLOC product
| Mode | Effort (PM) | Time (months) | Staff |
|---|---|---|---|
| Organic | 2.4 × 50^1.05 = 145.9 | 2.5 × 145.9^0.38 = 16.6 | 8.8 |
| Semi-detached | 3.0 × 50^1.12 = 239.9 | 2.5 × 239.9^0.35 = 17.0 | 14.1 |
| Embedded | 3.6 × 50^1.20 = 393.6 | 2.5 × 393.6^0.32 = 16.9 | 23.3 |
Answer (organic): effort about 146 person-months, time about 16.6 months, about 9 people.
Advantages
- Simple, transparent, well documented, quick early estimate.
Limitations
- Depends on accurate size (KLOC) estimate.
- Calibrated on old data (1970s projects); not ideal for modern agile, reuse or RAD.
- Ignores some factors in the basic form.
COCOMO II (1995 onward) updates the model with Application Composition, Early Design and Post-Architecture stages, uses function points or object points, and scale factors.
✓ Answer checked by Claude Opus 5.5 (high effort)