[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.