COCOMO Model
Cocomo (Constructive Cost Model) is a regression model based on LOC,
i.e number of Lines of Code. It is a procedural cost estimate model for
software projects and is often used as a process of reliably predicting the
various parameters associated with making a project such as size, effort,
cost, time, and quality. It was proposed by Barry Boehm in 1981 and is
based on the study of 63 projects, which makes it one of the best-
documented models.
The key parameters which define the quality of any software products,
which are also an outcome of the Cocomo are primarily Effort & Schedule:
• Effort: Amount of labor that will be required to complete a task. It
is measured in person-months units.
• Schedule: Simply means the amount of time required for the
completion of the job, which is, of course, proportional to the effort
put in. It is measured in the units of time such as weeks, and
months.
Different models of Cocomo have been proposed to predict the cost
estimation at different levels, based on the amount of accuracy and
correctness required. All of these models can be applied to a variety of
projects, whose characteristics determine the value of the constant to be
used in subsequent calculations.
These characteristics pertaining to different system types are mentioned
below. Boehm’s definition of organic, semidetached, and embedded
systems:
1. Organic – A software project is said to be an organic type if the team size
required is adequately small, the problem is well understood and has been
solved in the past and also the team members have a nominal experience
regarding the problem.
2. Semi-detached – A software project is said to be a Semi-detached type if
the vital characteristics such as team size, experience, and knowledge of the
various programming environment lie in between that of organic and
Embedded. The projects classified as Semi-Detached are comparatively less
familiar and difficult to develop compared to the organic ones and require
more experience and better guidance and creativity. Eg: Compilers or
different Embedded Systems can be considered Semi-Detached types.
3. Embedded – A software project requiring the highest level of complexity,
creativity, and experience requirement fall under this category. Such
software requires a larger team size than the other two models and also the
developers need to be sufficiently experienced and creative to develop such
complex models.
1. Basic COCOMO Model
2. Intermediate COCOMO Model
3. Detailed COCOMO Model
1. Basic Model –
E=a(KLOC)b
Time=c(EFFORT)d
Person required=effort/time
The above formula is used for the cost estimation of for the basic COCOMO
model, and also is used in the subsequent models. The constant values
a,b,c, and d for the Basic Model for the different categories of the system:
Software Projects a b c d
Organic 2.4 1.05 2.5 0.38
Semi-Detached 3.0 1.12 2.5 0.35
Embedded 3.6 1.20 2.5 0.32
The effort is measured in Person-Months and as evident from the formula is
dependent on Kilo-Lines of code. The development time is measured in
months. These formulas are used as such in the Basic Model calculations, as
not much consideration of different factors such as reliability, and expertise
is taken into account, henceforth the estimate is rough.
2. Intermediate Model – The basic Cocomo model assumes that the effort is
only a function of the number of lines of code and some constants evaluated
according to the different software systems. However, in reality, no system’s
effort and schedule can be solely calculated on the basis of Lines of Code.
For that, various other factors such as reliability, experience, and Capability.
These factors are known as Cost Drivers and the Intermediate Model utilizes
15 such drivers for cost estimation. Classification of Cost Drivers and their
Attributes:
(i) Product attributes –
• Required software reliability extent
• Size of the application database
• The complexity of the product
• Run-time performance constraints
• Memory constraints
• The volatility of the virtual machine environment
• Required turnabout time
• Analyst capability
• Software engineering capability
• Applications experience
• Virtual machine experience
• Programming language experience
• Use of software tools
• Application of software engineering methods
• Required development schedule
3. Detailed Model – Detailed COCOMO incorporates all characteristics of the
intermediate version with an assessment of the cost driver’s impact on each
step of the software engineering process. The detailed model uses different
effort multipliers for each cost driver attribute. In detailed cocomo, the whole
software is divided into different modules and then we apply COCOMO in
different modules to estimate effort and then sum the effort. The Six phases
of detailed COCOMO are:
1. Planning and requirements
2. System design
3. Detailed design
4. Module code and test
5. Integration and test
6. Cost Constructive model
Advantages of the COCOMO model:
1. Provides a systematic way to estimate the cost and effort of a
software project.
2. Can be used to estimate the cost and effort of a software project at
different stages of the development process.
3. Helps in identifying the factors that have the greatest impact on the
cost and effort of a software project.
4. Can be used to evaluate the feasibility of a software project by
estimating the cost and effort required to complete it.
Disadvantages of the COCOMO model:
1. Assumes that the size of the software is the main factor that
determines the cost and effort of a software project, which may not
always be the case.
2. Does not take into account the specific characteristics of the
development team, which can have a significant impact on the cost
and effort of a software project.
3. Does not provide a precise estimate of the cost and effort of a
software project, as it is based on assumptions and averages.
