THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject :Software Engineering
Unit :2 Module :Module-3
Empirical Estimation Models: The COCOMO Model
Boehm proposed COCOMO (Constructive Cost Estimation Model) in 1981.COCOMO is one
of the most generally used software estimation models in the world. COCOMO predicts the
efforts and schedule of a software product based on the size of the software.
The necessary steps in this model are:
1. Get an initial estimate of the development effort from evaluation of thousands of
delivered lines of source code (KDLOC).
2. Determine a set of 15 multiplying factors from various attributes of the project.
3. Calculate the effort estimate by multiplying the initial estimate with all the
multiplying factors i.e., multiply the values in step1 and step2.
The initial estimate (also called nominal estimate) is determined by an equation of the form
used in the static single variable models, using KDLOC as the measure of the size. To
determine the initial effort Ei in person-months the equation used is of the type is shown
below
Ei=a*(KDLOC)b
The value of the constant a and b are depends on the project type.
In COCOMO, projects are categorized into three types:
1. Organic
2. Semidetached
3. Embedded
1.Organic: A development project can be treated of the organic type, if the project deals with
developing a well-understood application program, the size of the development team is
reasonably small, and the team members are experienced in developing similar methods of
projects. Examples of this type of projects are simple business systems, simple inventory
management systems, and data processing systems.
2. Semidetached: A development project can be treated with semidetached type if the
development consists of a mixture of experienced and inexperienced staff. Team members
may have finite experience in related systems but may be unfamiliar with some aspects of the
order being developed. Example of Semidetached system includes developing a new
operating system (OS), a Database Management System (DBMS), and complex
inventory management system.
3. Embedded: A development project is treated to be of an embedded type, if the software
being developed is strongly coupled to complex hardware, or if the stringent regulations on
the operational method exist. For Example: ATM, Air Traffic control.
For three product categories, Bohem provides a different set of expression to predict effort (in
a unit of person month)and development time from the size of estimation in KLOC(Kilo Line
of code) efforts estimation takes into account the productivity loss due to holidays, weekly
off, coffee breaks, etc.
According to Boehm, software cost estimation should be done through three stages:
1. Basic Model
2. Intermediate Model
3. Detailed Model
COURSE : SOFTWARE ENGINEERING [UNIT-NO : 2 MODULE-NO:3] 1
THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject : Software Engineering
Unit : 2 Module :Module-3
1. Basic COCOMO Model: The basic COCOMO model provide an accurate size of the
project parameters. The following expressions give the basic COCOMO estimation model:
Effort=a1*(KLOC) a2 PM
Tdev=b1*(efforts)b2 Months
Where
KLOC is the estimated size of the software product indicate in Kilo Lines of Code,
a1,a2,b1,b2 are constants for each group of software products,
Tdev is the estimated time to develop the software, expressed in months,
Effort is the total effort required to develop the software product, expressed in person
months (PMs).
Estimation of development effort
For the three classes of software products, the formulas for estimating the effort based on the
code size are shown below:
Organic: Effort = 2.4(KLOC) 1.05 PM
Semi-detached: Effort = 3.0(KLOC) 1.12 PM
Embedded: Effort = 3.6(KLOC) 1.20 PM
Estimation of development time
For the three classes of software products, the formulas for estimating the development time
based on the effort are given below:
Organic: Tdev = 2.5(Effort) 0.38 Months
Semi-detached: Tdev = 2.5(Effort) 0.35 Months
Embedded: Tdev = 2.5(Effort) 0.32 Months
Some insight into the basic COCOMO model can be obtained by plotting the estimated
characteristics for different software sizes. Fig shows a plot of estimated effort versus product
size. From fig, we can observe that the effort is somewhat superliner in the size of the
software product. Thus, the effort required to develop a product increases very rapidly with
project size.
Example1: Suppose a project was estimated to be 400 KLOC. Calculate the effort and
development time for each of the three model i.e., organic, semi-detached & embedded.
Solution: The basic COCOMO equation takes the form:
Effort=a1*(KLOC) a2 PM
Tdev=b1*(efforts)b2 Months
Estimated Size of project= 400 KLOC
(i)Organic Mode
E = 2.4 * (400)1.05 = 1295.31 PM
D = 2.5 * (1295.31)0.38=38.07 PM
(ii)Semidetached Mode
E = 3.0 * (400)1.12=2462.79 PM
D = 2.5 * (2462.79)0.35=38.45 PM
(iii) Embedded Mode
E = 3.6 * (400)1.20 = 4772.81 PM
D = 2.5 * (4772.8)0.32 = 38 PM
Course : Software Engineering [Unit-No : 2 MODULE-No:3] 2
THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject : Software Engineering
Unit : 2 Module :Module-3
2. Intermediate Model: The basic Cocomo model considers that the effort is only a function
of the number of lines of code and some constants calculated according to the various
software systems. The intermediate COCOMO model recognizes these facts and refines the
initial estimates obtained through the basic COCOMO model by using a set of 15 cost drivers
based on various attributes of software engineering.
Classification of Cost Drivers and their attributes:
(i) Product attributes -
o Required software reliability extent
o Size of the application database
o The complexity of the product
Hardware attributes -
o Run-time performance constraints
o Memory constraints
o The volatility of the virtual machine environment
o Required turnabout time
Personnel attributes -
o Analyst capability
o Software engineering capability
o Applications experience
o Virtual machine experience
o Programming language experience
Project attributes -
o Use of software tools
o Application of software engineering methods
o Required development schedule
The cost drivers are divided into four categories:
Course : Software Engineering [Unit-No : 2 MODULE-No:3] 3
THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject : Software Engineering
Unit : 2 Module :Module-3
Course : Software Engineering [Unit-No : 2 MODULE-No:3] 4
THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject : Software Engineering
Unit : 2 Module :Module-3
Intermediate COCOMO equation:
E=ai (KLOC) bi*EAF
D=ci (E)di
Coefficients for intermediate COCOMO
3. Detailed COCOMO Model:Detailed COCOMO incorporates all qualities of the standard
version with an assessment of the cost driver?s effect on each method of the software
engineering process. The detailed model uses various effort multipliers for each cost driver
property. In detailed cocomo, the whole software is differentiated into multiple modules, and
then we apply COCOMO in various modules to estimate effort and then sum the effort.
The Six phases of detailed COCOMO are:
1. Planning and requirements
2. System structure
3. Complete structure
4. Module code and test
5. Integration and test
6. Cost Constructive model
Course : Software Engineering [Unit-No : 2 MODULE-No:3] 5
THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject : Software Engineering
Unit : 2 Module :Module-3
The effort is determined as a function of program estimate, and a set of cost drivers are given
according to every phase of the software lifecycle.
Make/Buy Decision
It is often more cost effective to acquire rather than develop software
Managers have many acquisition options
Software may be purchased (or licensed) off the shelf
“Full-experience” or “partial-experience” software components may be
acquired and integrated to meet specific needs
Software may be custom built by an outside contractor to meet the purchaser’s
specifications
The make/buy decision can be made based on the following conditions
Will the software product be available sooner than internally developed
software?
Will the cost of acquisition plus the cost of customization be less than the cost
of developing the software internally?
Will the cost of outside support (e.g., a maintenance contract) be less than the
cost of internal support?
Software Risk Management
A software project can be concerned with a large variety of risks. In order to be adept to
systematically identify the significant risks which might affect a software project, it is
essential to classify risks into different classes. The project manager can then check which
risks from each class are relevant to the project.
There are three main classifications of risks which can affect a software project:
1. Project risks
2. Technical risks
3. Business risks
1. Project risks: Project risks concern differ forms of budgetary, schedule, personnel,
resource, and customer-related problems. A vital project risk is schedule slippage. Since the
software is intangible, it is very tough to monitor and control a software project. It is very
tough to control something which cannot be identified. For any manufacturing program, such
as the manufacturing of cars, the plan executive can recognize the product taking shape.
2. Technical risks: Technical risks concern potential method, implementation, interfacing,
testing, and maintenance issue. It also consists of an ambiguous specification, incomplete
specification, changing specification, technical uncertainty, and technical obsolescence. Most
technical risks appear due to the development team's insufficient knowledge about the
project.
Course : Software Engineering [Unit-No : 2 MODULE-No:3] 6
THE BHOPAL SCHOOL OF SOCIAL SCIENCES
Class :BCA Subject : Software Engineering
Unit : 2 Module :Module-3
3. Business risks: This type of risks contain risks of building an excellent product that no one
need, losing budgetary or personnel commitments, etc.
REFERENCES :
(1) https://www.tutorialspoint.com
(2) https://javatpoint.com
(3) https://www.simplilearn.com//
(4) https://www.tutorialandexample.com/
*Edited & Compiled for Reference Purpose for Students by :
SHILPA JACKSON
Assistant Professor
The Department of Computer
Applications
The Bhopal School of Social Sciences
Course : Software Engineering [Unit-No : 2 MODULE-No:3] 7
