The COCOMO (Constructive Cost Estimation Model) Model - Basic, Intermediate and Complete COCOMO

COCOMO (Constructive Cost Estimation Model) was proposed by Boehm. COCOMO is a widely spread model that combines statistical figures, mathematical equations, and expert judgement. COCOMO is an open model. It includes the underlying cost estimation equations, every assumption made in the model, every definition and the costs included in an estimate are explicitly stated.

- COCOMO estimates are more objective and repeatable than estimates made by methods relying on proprietary models.
- COCOMO can be calibrated to reflect your software development environment, and to produce more accurate estimates.

Software cost estimation should be done through three stages:
- Basic COCOMO : It is a single-valued, static model in which the development effort is estimated as a function of program size.
Effort = a1 х (KLOC)^a2 PM
Tdev = b1 x (Effort)^b2 Months
where:
• KLOC is the estimated size of the software product expressed in Kilo Lines of Code,
• a1, a2, b1, b2 are constants for each category of software products,
• Tdev is the estimated time to develop the software, expressed in
months,
• Effort is the total effort required to develop the software product.

- Intermediate COCOMO : It computes software development effort as a function of program size and a set of fifteen "cost drivers". It takes into account factors such as required product reliability, database size, execution and storage constraints, personnel aptitude, and the use of software tools.

- Complete COCOMO : The main shortcoming of basic and intermediate COCOMO model is that they consider a software product as a single homogeneous entity. The system is made up of sub-systems which have their own characteristics. Sub-systems may have different inherent development complexity, reliability requirements may be high, development team experience.
The complete COCOMO model considers these differences in characteristics of the subsystems and estimates the effort and development time as the sum of the estimates for the individual subsystems.