What is COCOMO model? Explain different sub models of COCOMO 2 model.

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COCOMO (Constructive Cost Model)

- The COCOMO (Constructive Cost Model) is one of the most popularly used software cost estimation models i.e. it estimates or predicts the effort required for the project, total project cost, and scheduled time for the project. 

- This model depends on the number of lines of code for software product development. It was developed by software engineer Barry Boehm in 1981.

- The COCOMO estimates the cost for software product development in terms of effort (resources required to complete the project work) and schedule (time required to complete the project work) based on the size of the software product. 

- It estimates the required number of Man-Months (MM) for the full development of software products.


Example of COCOMO Model

Example: A project size of 200 KLOC is to be developed. The software development team has average experience on similar types of projects. The project schedule is not very tight. Calculate the Effort, development time, average staff size, and productivity of the project.

Solution: The semidetached mode is the most appropriate mode, keeping in view the size,

schedule and experience of development time.

Hence E=3.0(200)1.12=1133.12PM

D=2.5(1133.12)0.35=29.3PM

P= 176 LOC/PM


This model incorporates a range of sub-models that produce increasingly detailed software cost estimates. The sub-models in COCOMO 2 are:

a) Application composition model: 

It is used when software is composed of existing parts. Supports prototyping projects and projects where there is extensive reuse based on standard estimates of developer productivity in an application (object) points/month. It Takes the CASE tool use into account. The formula is:

PM = NOP/PROD = (Object Points x (1 - % reuse/100))/PROD

Where PM is the effort in person-months

NOP is the new object points

PROD is productivity.


b) Early design model:

This model is used when requirements are available but the design has not yet started. In this model, Estimates can be made after the requirements have been agreed upon. The empirical formula used to calculate a person's month is: PM=AXSizeBXM

Where M= PERS×RCPX×RUSEXPDIF×PREX×FCILX SCED

A= 2.94 in an initial calibration

Size in KLOC

B varies from 1.1 to 1.24 depending on the novelty of the project, development flexibility, risk management approaches, and process maturity.


c) Reuse-oriented Model:-

This model is used to compute the effort of integrating reusable components. A major effort is required to integrate automatically generated code. The empirical formula is:-

PMAuto = (ASLOC x (AT/100))/ATPROD

Where, ASLOC - No. LOC that has to be adapted

AT - % of adapted code that is automatically generated


d) Post-architecture model. 

This model is used once the system architecture has been designed and more information about the system is available. In this model, we use the same formula as early design estimates: PM - Ax Size x M

Where Size estimate for the software should be more accurate at this stage. It takes into consideration the factors like New code to be developed, reworks required to support change, and the extent of possible reuse.



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