[The Constructive Cost Model]

By

G. Gopi Krishna Reddy

COCOMO OUTLINEINTRODUCTIONTHE BASIC MODEL

EquationsLimitations

INTERMEDIATE MODELADVANCE MODEL

COCOMOCOCOMO is one of the most widely used software estimation model in the world.It was developed by BARRY BOEHM in 1981

COCOMO predicts the effort and schedule for a software product development based on inputs relating to the size of the software and a number of cost drivers that affect productivity

Types Of Forms

COCOMOMODEL

Basic COCOMOIntermediateCOCOMO

AdvancedCOCOMO

COCOMO can be applied to three classes of software projects.

a) organic mode

- Relative small ,simple software projects.

b) semi-detached mode

- For intermediate software projects.

c) Embedded mode

- A software project that must be developed within set of hardware , software and operational constraints.

Basic COCOMOIt is a static-valued modelComputes software development effort as a function

of program size expressed in estimated lines of code.

When to use:• Basic COCOMO is good for quick, early,

rough order of magnitude estimates of software costs

Basic Model: Equations

Mode Effort Schedule

Organic E=2.4*(KDSI)1.05 TDEV=2.5*(E)0.38

Semidetached E=3.0*(KDSI)1.12 TDEV=2.5*(E)0.35

Embedded E=3.6*(KDSI)1.20 TDEV=2.5*(E)0.32

Basic COCOMO Model:LimitationsIts accuracy is necessarily limited because of

its lack of factors which have a significant influence on software costs

The Basic COCOMO estimates are within a factor of 1.3 only 29% of the time, and within a factor of 2 only 60% of the time

Intermediate COCOMOComputes effort as function of program size and

a lost of cost drivers that include subjective assessment of product, hardware, personal and project attributes.

When to use:The Intermediate Model can be applied across

the entire software product for easily and rough cost estimation during the early stage

or it can be applied at the software product component level for more accurate cost estimation in more detailed stages

Intermediate Model: Equations

Mode Effort Schedule

Organic E=EAF*3.2*(KDSI)1.05 TDEV=2.5*(E)0.38

Semi- E=EAF*3.0*(KDSI)1.12 TDEV=2.5*(E)0.35

detached

Embedded E=EAF*2.8*(KDSI)1.20 TDEV=2.5*(E)0.32

Intermediate Model:LimitationsThe Intermediate Model estimates are within

20% of the actuals 68% of the timeIts effort multipliers are phase-insensitiveIt can be very tedious to use on a product

with many components

Advanced COCOMOIncorporates all characteristics of the intermediate version

with an assessment of the cost driver’s impact on each step of the software engineering process.

When to use :The Detailed Model can estimate the staffing,

cost, and duration of each of the development phases, subsystems, modules

It allows you to experiment with different development strategies, to find the plan that best suits your needs and resources

Advanced Model: Equations

Detailed Model uses the same equations for estimations as the Intermediate Model

Detailed Model uses a very complex procedure to calculate estimation. The procedure uses the DSIs for subsystems and modules, and module level and subsystem level effort multipliers as inputs

Advanced Model: Limitations

Requires substantially more time and effort to calculate estimates than previous models

Detailed Model estimates are within 20% of the actuals 70% of the time

ConclusionIt is well documented,available in the public domain and

supported by public domain and commercial tools.It has been widely used and evaluated in a range of

organizations.