COCOMO Model

The Constructive Cost Model (COCOMO) 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. It is
a Software Cost Estimation Model that helps predict the effort, cost, and schedule required
for a software development project.

What is the COCOMO Model?

COCOMO Model 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. The key parameters that define the quality
of any Software Product, which are also an outcome of COCOMO, are primarily effort and
schedule.

Types of Projects in COCOMO Model

In the COCOMO model, software projects are categorized into three types based on their
complexity, size, and the development environment. These types are:

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 environments lie in between
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 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 falls 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.

Comparison of Types of Projects in COCOMO Model

Here is the Comparison in detail where the project types of COCOMO Model
Aspects Organic Semidetached Embedded
 Aspects Organic Semidetached Embedded

300 and above

2 to 50 KLOC 50-300 KLOC
Project Size KLOC

Complexity Low Medium High

Some experienced as
Highly Mixed experience,
Team well as inexperienced
experienced includes experts
Experience staff

Flexible, fewer Somewhat flexible, Highly rigorous,

Environment constraints moderate constraints strict requirements

Effort
Equation
E = 2.4(400)1.05 E = 3.0(400)1.12 E = 3.6(400)1.20

Simple payroll New system interfacing Flight control

Example system with existing systems software

Structure of COCOMO 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.

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: This initial phase involves defining the scope, objectives,
and constraints of the project. It includes developing a project plan that outlines the
schedule, resources, and milestones
2. System design: : In this phase, the high-level architecture of the software system is
created. This includes defining the system’s overall structure, including major components,
their interactions, and the data flow between them.
3. Detailed design: This phase involves creating detailed specifications for each component
of the system. It breaks down the system design into detailed descriptions of each module,
including data structures, algorithms, and interfaces.
4. Module code and test: This involves writing the actual source code for each module or
component as defined in the detailed design. It includes coding the functionalities,
implementing algorithms, and developing interfaces.
5. Integration and test: This phase involves combining individual modules into a complete
system and ensuring that they work together as intended.
6. Cost Constructive model: The Constructive Cost Model (COCOMO) is a widely used
method for estimating the cost and effort required for software development projects.
7.
Importance of the COCOMO Model
1. Cost Estimation: To help with resource planning and project budgeting, COCOMO offers
a methodical approach to software development cost estimation.
2. Resource Management: By taking team experience, project size, and complexity into
account, the model helps with efficient resource allocation.
3. Project Planning: COCOMO assists in developing practical project plans that include
attainable objectives, due dates, and benchmarks.
4. Risk management: Early in the development process, COCOMO assists in identifying and
mitigating potential hazards by including risk elements.
5. Support for Decisions: During project planning, the model provides a quantitative
foundation for choices about scope, priorities, and resource allocation.
6. Benchmarking: To compare and assess various software development projects to industry
standards, COCOMO offers a benchmark.
7. Resource Optimization: The model helps to maximize the use of resources, which raises
productivity and lowers costs.

Types of COCOMO Model

There are three types of COCOMO Model:

1. Basic COCOMO Model: The Basic COCOMO model is a straightforward way to

estimate the effort needed for a software development project. It uses a simple mathematical
formula to predict how many person-months of work are required based on the size of the
project, measured in thousands of lines of code (KLOC).
It estimates effort and time required for development using the following expression:

E = a*(KLOC)b PM
Tdev = c*(E)d
Person required = Effort/ Time
Where,
 E is effort applied in Person-Months
 KLOC is the estimated size of the software product indicate in Kilo Lines of Code
 Tdev is the development time in months
a, b, c are constants determined by the category of software project given in below table.
The above formula is used for the cost estimation of 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
software projects is:

Software
Projects a b c d

Organic 2.4 1.05 2.5 0.38

Semi-
3.0 1.12 2.5 0.35
Detached

Embedded 3.6 1.20 2.5 0.32

1. 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.
2. 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.

Example of Basic COCOMO Model:

Suppose that a Basic project was estimated to be 400 KLOC (kilo lines of code). Calculate
effort and time for each of the three modes of development. All the constants value provided
in the following table:

Solution: From the above table we take the value of constant a,b,c and d.

1. For organic mode,

 effort = 2.4 × (400)1.05 ≈ 1295 person-month.
 dev. time = 2.5 × (1295)0.38 ≈ 38 months.
2. For semi-detach mode,
 effort = 3 × (400)1.12 ≈ 2462 person-month.
 dev. time = 2.5 × (2462)0.35 ≈ 38 months.
3. For Embedded mode,
 effort = 3.6 × (400)1.20 ≈ 4772 person-month.
 dev. time = 2.5 × (4772)0.32 ≈ 38 months.

2. Intermediate COCOMO 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 based on Lines of Code. For
that, various other factors such as reliability, experience, and Capability. These factors are
known as Cost Drivers (multipliers) and the Intermediate Model utilizes 15 such drivers for
cost estimation.
Classification of Cost Drivers and their Attributes: The cost drivers are divided into four
categories-

Product attributes:
 Required Software Reliability extent
 Size of the application database
 The complexity of the product

Hardware attributes:
 Run-time performance constraints
 Memory constraints
 The volatility of the virtual machine environment
 Required turnabout time

Personal attributes:
 Analyst capability
 Software engineering capability
 Application experience
 Virtual machine experience
 Programming language experience

Project attributes:
 Use of Software Tools.
 Application of Software Engineering Methods.
 Required development schedule.

Each of the 15 such attributes can be rated on a six-point scale ranging from “very low” to
“extra high” in their relative order of importance. Each attribute has an effort multiplier fixed as
per the rating. Table give below represents Cost Drivers and their respective rating:
The Effort Adjustment Factor (EAF) is determined by multiplying the effort multipliers
associated with each of the 15 attributes.

The Effort Adjustment Factor (EAF) is employed to enhance the estimates generated by the
basic COCOMO model in the following expression:

Intermediate COCOMO Model equation:

E = a*(KLOC)b * EAF PM
Tdev = c*(E)d
Where,
 E is effort applied in Person-Months
 KLOC is the estimated size of the software product indicate in Kilo Lines of Code
 EAF is the Effort Adjustment Factor (EAF) is a multiplier used to refine the effort estimate
obtained from the basic COCOMO model.
 Tdev is the development time in months

a, b, c are constants determined by the category of software project given in below table.
The constant values a, b, c, and d for the Basic Model for the different categories of the
software projects is:
 Software
Projects a b c d

Organic 3.2 1.05 2.5 0.38

Semi-
3.0 1.12 2.5 0.35
Detached

Embedded 2.8 1.20 2.5 0.32

3. Detailed COCOMO Model

Detailed COCOMO goes beyond Basic and Intermediate COCOMO by diving deeper into
project-specific factors. It considers a wider range of parameters, like team experience,
development practices, and software complexity. By analyzing these factors in more detail,
Detailed COCOMO provides a highly accurate estimation of effort, time, and cost for software
projects. It’s like zooming in on a project’s unique characteristics to get a clearer picture of
what it will take to complete it successfully.

Advantages of the COCOMO Model

1. Systematic cost estimation: Provides a systematic way to estimate the cost and effort of
a software project.
2. Helps to estimate cost and effort: This can be used to estimate the cost and effort of a
software project at different stages of the development process.
3. Helps in high-impact factors: Helps in identifying the factors that have the greatest
impact on the cost and effort of a software project.
4. Helps to evaluate the feasibility of a project: This 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 project size as the main factor: 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 count development team-specific characteristics: 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. Not enough precise cost and effort estimate: This does not provide a precise estimate
of the cost and effort of a software project, as it is based on assumptions and averages.
COCOMO-II is the revised version of the original Cocomo (Constructive Cost Model) and was
developed at the University of Southern California. It is the model that allows one to estimate
the cost, effort, and schedule when planning a new software development activity.

1. End User Programming: Application generators are used in this sub-model.

End user write the code by using these application generators. For Example,
Spreadsheets, report generator, etc.

2. Intermediate Sector:

 Application Generators and Composition Aids: This category will create largely
prepackaged capabilities for user programming. Their product will have many reusable
components. Typical firms operating in this sector are Microsoft, Lotus, Oracle, IBM,
Borland, Novell.

 Application Composition Sector: This category is too diversified and to be handled by

prepackaged solutions. It includes GUI, Databases, domain specific components such as
financial, medical or industrial process control packages.

 System Integration: This category deals with large scale and highly embedded systems.

3. Infrastructure Sector: This category provides infrastructure for the software

development like Operating System, Database Management System, User Interface
Management System, Networking System, etc.
Stages of COCOMO II

1. Stage-I
It supports estimation of prototyping. For this it uses Application Composition Estimation
Model. This model is used for the prototyping stage of application generator and system
integration.
2. Stage-II
It supports estimation in the early design stage of the project, when we less know about it. For
this it uses Early Design Estimation Model. This model is used in early design stage of
application generators, infrastructure, system integration.
3. Stage-III
It supports estimation in the post architecture stage of a project. For this it uses Post
Architecture Estimation Model. This model is used after the completion of the detailed
architecture of application generator, infrastructure, system integration.