Code Project Software project cost estimates using COCOMO II Model

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Development Lifecycle » Design and Architecture » Methodologies

Software Project Cost Estimates
Using COCOMO II Model
By Stan1964

Describes simple COCOMO II cost estimation steps for a real software project.
Windows, Visual Studio, CEO,
Architect, Dev
Posted: 10 Jan 2005
Views: 96,075
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Contents
Introduction •
Audience •
Sample Project Description and Scope •
Introduction to COCOMO II Estimates •
Counting SLOC in the Project •
Using Costar Estimation Tool •
Summary of Cost Estimation Results •
Conclusion •
References •
Appendix A: Cost Drivers •
Appendix B: Scale Factors •
Introduction
This article provides a sample of COCOMO II cost estimate for a real
project, and concentrates on outlining basic how-to when project
manager needs some advice on making simple cost estimates and
tools that can be used.
Audience
The article is

intended for those who are new to project cost estimation
techniques, and those who would like to have a feedback on COCOMO
II model. My objective is to describe in a simple way basic cost
estimation steps, tools and assumptions,
having a real project in mind,
and supplying only necessary details on the project itself.
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/>Sample Project Description and

Scope
A bioinformatics company, providing advanced methods for data
mining of genetic information, intends to construct a distributed
application for analysis and navigation of biological networks. As part
of this project, a database provider that exposes simple interfaces to
UI programmer and hides complexities of the data layer should be
build. As soon as the scope of this task is broadly defined as such, it is
sliced into a separate project. The content of this article targets cost
estimation perspective of the latter project.
The company has already made work on inception phase, and

provided
the document describing the project concept. The customer has the
following preferences:
Transfer existing SQL Server database (~1 GB) hosted on
Windows to PostgreSQL data end hosted on Linux.
1.
Build components for this project using Java. The main
component is database provider.
2.
Since the project is small, the elaboration phase (or detailed
design phase) is not necessary.
3.
Project has time constraints. 4.
Said above is a short scope definition for the project provided by the
company. As in many projects, the next important step is to make cost

estimates.
Introduction to COCOMO II Estimates
COCOMO (Constructive Cost Model) is a model that allows software
project managers to estimate project cost and duration. It was
developed initially (COCOMO 81) by Barry Boehm in the early
eighties
2)
. The COCOMO II
1)
model is a COCOMO 81 update to address
software development practices in the
1990's and 2000's. The model is
by now invigorative software engineering artifact that has, from
customer perspective, the following features:

The model is simple and well tested •
Provides about 20% cost and 70% time estimate accuracy •
In general, COCOMO II estimates project cost, derived directly from
person-months effort, by assuming the cost is basically dependent on
total physical size of all project files, expressed in thousands single
lines of code (KSLOC). The estimation formulas have the form:
Collapse Copy Code
Effort (in person-months) = a x KSLOC
b
where coefficient
a
is about 3 (2.94), and scaling factor
b
is close to 1
(1.0997).
There are similar COCOMO formulas for project duration (expressed in
months) and average size of project team. Interestingly, project
duration in COCOMO is approximately cube root of effort (in person-
months).
ASP.NET Web Hosting


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/>In practice, COCOMO parameters can be greatly different from its

typical values. COCOMO II provides classification of factors that can
have an influence on project cost, and lets you make better
approximation of coefficients and scaling factors for your particular
project. As the result of adjustment, 
a
 coefficient value falls
between 0.056  120. See Appendix A for COCOMO II list of
adjustment factors that affect first parameter. Model-driven
adjustment of scaling factor 
b
 is new in COCOMO II model and
reflects latest trends in software engineering. You can see scaling
factors descriptions in Appendix B.
Many project managers used to negotiate project costs with trade-off
triangle and trade-off matrix in terms of product functionality, quality,
and schedule. If this is a case for you, you might be intrigued how
COCOMO II adjustment parameters fit into this picture. The answer is
that COCOMO II parameters can be viewed as two sets of parameters.
The first set is external and can be loosely matched to trade-off
triangle/matrix view and its vocabulary is frequently used while
negotiating costs with stakeholder, and the second set is COCOMO II
internal and usually cannot be used for this purpose. In this trade-off
triangle/matrix perspective, schedule is loosely corresponding to
SCED

(required development schedule), quality to
RELY

(required reliability),
and functionality to a combination of

CPLX
(product complexity),
DATA

(database size),
TIME
(execution time),
DOCU
(documentation match
to life-cycle needs), and occasionally
RUSE
,
STOR
,
PVOL
parameters.
COCOMO II internal parameters such as parameters for evaluation of
personnel capabilities/experiences, used project tools and others are
obviously important for project cost estimates, but usually are not a
subject of cost communications with stakeholder.
There are well-approbated COCOMO II tools on the market that
calculate these parameters for you, asking questions about particular
project in natural language, such as How experienced is the
development team? or How tough is the project schedule? and,
thus, hiding model details in the background.
COCOMO II supercedes earlier version of COCOMO such as COCOMO
81, Ada COCOMO, which are considered by now as outdated. The
model simplifies inception phase cost estimates by reducing the total
number of parameters to seven (from 15 in the original COCOMO
model), and suggests to use functional points for inception phase, and

SLOC for later, more accurate phases. In fact, COCOMO II reduces
controversy of what project metrics to use  SLOC or functional points

making the new model more flexible.
Comparing to classical COCOMO 81, COCOMO II introduces five scale
factors, at least three
of them are directly related to PM activities, and,
thus, raises the role of project management in reducing project costs:
Takes into account process maturity in the organization (CMM
levels)
•
Takes into account the degree to which project architecture
exists and is stabilized before construction phase
•
Takes into account relationships perspective: team cohesion,
relations with stockholder
•
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/>Now, I will demonstrate basic estimation steps in COCOMO II model.
To make actual estimates, Ill use the
source code for this project that
can be downloaded from here.
If you have project source code, and some project details, this is all
you need to make a simple cost estimate. Surely, you dont have a

source code before starting your project, and this approach is more
like post-mortem analysis. OK, this is my intention! By doing so,
some chronological accuracy will be lost, but real cost estimate will be
more correct.
Counting SLOC in the Project
To
make actual estimations, you need at first to figure out SLOC count
for each of the components and use these counts in COCOMO model.
To put it simple, SLOC (single line of code) is a physical line of code in
your program except comments. Of course, you can use your favorite
IDE and look onto the status bar in order to see how much line the
code contains. It might be acceptable as a first-
time estimate of SLOC.
To be more accurate, you need to exclude comments and blank lines.
Albeit, it is an easy procedure for a small project; for a larger project
with many thousands of SLOC and multiple files, the choice of
automated SLOC counting tool would be a more natural option.
I decided to use for these estimates the CodeCounter program that
has a friendly UI, and can count SLOC in many languages including
Java, C/C++, SQL (and flavors), HTML/XML. The CodeCounter
program can be downloaded for 30-day evaluation from here.
The case study source project files reflect four tasks accomplished
during this project:
Create PostgreSQL database, indexes, write pgSQL (close to
PL/SQL) stored procedures.
•
Build a Java component (composed of multiple JavaBeans) that
encapsulates an applications basic logic, and serves as
database provider.
•

Build a servlet, considered as a separate component, to dispatch
UI calls to the core Java component.
•
Write simple HTML pages to test database provider. •
In other words, the sample project source files correspond to four
ingredients written in SQL, Java, and HTML/XML. It is convenient
before counting to make separate folders corresponding to the project
components and place there files to count.
The result of separate SLOC count in all project folders is the
following:
Folder Total SLOC
1 SQL Files 414
2 Java DB Provider Files 345
3 Java Servlet 156
4 Web Files 113
Table 1.
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/>COCOMO generally recommends using standard SLOC counting
programs that can perform line counting for code written in different
languages. One of these programs is C-based CodeCount (command-
line program without UI). You can download its source from Center for
Software Engineering (you need to compile it by yourself too!), and
count SLOC in C, C++, Java, and other languages. The benefit of
CodeCount is that it is free, and was used for many years by many

companies for code counting.
Making COCOMO II estimates Using Costar
Estimation Tool
Of course, you can use COCOMO II as it is: choose model, formulas,
figure out the values for parameters, and manually calculate project
costs. I believe it is a matter what tool you prefer in every spring,
filling out tax forms  just simple calculator or automated software
tools. Allegedly, you prefer (you can opt to skip this section if Im
wrong!) the latter choice, and therefore, I would cover in this section
one of the specific tools for making COCOMO II estimates.
Ive selected Costar 7.0 COCOMO II tool since it has a convenient
interface and concise help. The program is licensed to over than one
million customers. Costar 7.0 30-day demo can be downloaded from
here.
Generally, you create a main component and subcomponents
corresponding to separate tasks of your project. The main component
serves basically as the Costar project root for all other components,
and is a place to summarize all estimates. It is not supposed to be
associated with your project files. You need to create subcomponents
for every project
task, and type manually total SLOC count for the task
from the SLOC counting program.
For this sample project (see Costars costar_dbprovider.cst project
file for this project in cocomo2.zip), Ive created the main (root)
component and four subcomponents:
db_provider
1.
servlet
2.
database_scripts

3.
ui_web_testing
4.
Now, when initial state of components is set up in the Costar project,
we can start making actual COCOMO II estimates. Albeit the total cost
of the project in COCOMO models is largely determined by total SLOC
count, adjustment and scaling parameters for a real project can vary
project costs in hundreds of times. As was mentioned above,
there are
two sets of additional parameters that are used to make COCOMO II
estimates more accurate. The first set, 17 cost drivers, are largely
inherited
from COCOMO 81 model, and the second set, 5 scale drivers,
are new in COCOMO II model.
The method of setting these parameters in a real project is rather
straightforward. As a project manager, you need to gather information
about most important sides of your project such as required product
characteristics,
required schedule, required product quality, experience
and capability of project team, project infrastructure readiness and
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/>maturity. Next comes the delicate part of making assumptions about
the values of COCOMO II parameters that correspond to the
information collected.

Since my aim is to make an
introduction to COCOMO II techniques and
terminology based on real project, I will only briefly describe
assumptions that I made for the case study project. All COCOMO II
parameters not mentioned below are set to their nominal value equal
to 1. The project was characterized by:
Scaling factors and product characteristics
Accomplished inception phase, but the
major lack of documented
architecture since stockholders considered this project as rather
small and not made elaboration phase as a separate phase.
(
RESL
scale factor is very low).
•
The development team was familiar with basic concepts of
software development methodology, but the software process
maturity was close to initial CMM stages (
PMAT
scale factor,
describing CMM level, is low).
•
Medium-size database backend (~1 GB) with about 20 tables
and 100 indexes (
DATA
cost driver is very high).
•
Schedule and personnel
The project
schedule was characterized by fixed time limitations,

limited time for new
team members to accommodate themselves
to the environment and tasks, which
means that schedule can be
considered as tough (
SCED
scheduling parameter is high).
•
Team members were experienced more than average in
programming languages such as C/C++, but were new to Java
development (
PCAP
, programmer capabilities is high, and
LTEX
,
language/tool experience, cost driver is low).
•
Team members were experienced more than average in
Windows environments, but were not especially experienced in
the latest Linux developments (
PLEX
, platform experience, cost
driver is low).
•
Interestingly, COCOMO II predicts that selection of highly
capable development team albeit not particularly experienced in
language, tools, and platform justifies itself for a project:
Collapse Copy Code
PCAP
[high=0.88]x

LTEX
[low=1.09]x
PLEX
[low=1.09] =1.04 ~ 1
There was no separate role for an analyst. This factor decreases
teams analytical capabilities. This is not a standard situation in
COCOMO model, which has
ACAP
parameter to account for
analyst capabilities. It seems possible to take into account not
filled analyst position in COCOMO II by setting analyst
capabilities parameter to lower value (
ACAP
, analyst capabilities
is low).
•
Finally, the pictures 2 and 3 taken from Costar project show all
COCOMO II cost drivers and scale factors along with their values:
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/>Picture 2.
Picture 3.
Notice that Costar lets you see equations that were used for final cost
estimates, as on picture 4:
Picture 4.

Summary of Cost Estimation Results
The overall result of COCOMO II estimates demonstrated in the report
obtained from Costar project:
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/>Picture 5.
The report says that project cost is
$23,000 and project duration is 4.6
months ($5000 was taken as an average monthly developer salary).
Conclusion
This brief article shows how to make cost estimates for a sample
project, and outlines basic steps, terms, and tools used. In a
smallsize or even intermediatesize project, there is a temptation to
cut off traditional sides of development that were widely accepted in
the nineties and actively used now. Obviously, ad hoc estimates are
prone to error. Cost estimation tools make it easy for you to
clarify not
only an expected project cost and duration, but also prompt you to
verify all basic sides of a software project by providing clear, compact,
and concise terms, methodology, which are tested on a wide range of
real-life projects, and, thus, reduce essentially project risks, and
provide reasonable grounds for communication with a project
stockholder.
References
Software Cost Estimation With COCOMO II, Prentice Hall,

2000.
1.
Software Engineering Economics by Barry Boehm, Prentice
Hall, 1981.
2.
Appendix A: Cost Drivers
There are multiple factors that effect project cost. COCOMO II model
defines 17 parameters called cost drivers that have a major influence
on project cost.
Project manager can determine
cost drivers based on project specifics,
and use them to adjust first coefficient in formula:
Collapse Copy Code
a = 2.94 x EAF
where EAF (Effort Adjustment Factor) is obtained by multiplication of
17 parameters, which:
All have a nominal value equal to 1.0. •
Most of them can have values: very low, low, nominal, high,
very high (extra low, extra high can be also considered).
•
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/>The range of majority of cost driver values falls between 0.5-
1.5,
and maximum value exceeds minimum value no more than

50%. Two exceptions are product complexity (
CPLX
) and analyst
capability (
ACAP
), where max/min value can be as high as 2.
•
SITE
,
RUSE
,
DOCU
,
PVOL
,
PCON
factors (marked with bold) are
new in COCOMO II, and reflect trends in software development
of late ninetieth, and 2000+ years.
•
The following table provides a list of COCOMO II adjustment factors.
Notice that the second column shows factors for this case study
project.

Cost
Driver
Sample Project
Value
Description
1

DATA
high Database size.
2
CPLX
nominal Product complexity.
3
TIME
nominal Execution time constraint.
4
STOR
nominal Main storage constraint.
5
RUSE
nominal Required reusability.
6
DOCU
nominal
Documentation match to life-cycle
needs.
7
PVOL
nominal Platform volatility.
8
SCED
very high Scheduling factor.
9
RELY
nominal Required reliability.
10
TOOL

nominal Use of software tools.
11
APEX
nominal Application experience.
12
ACAP
low Analyst capability.
13
PCAP
high Programmer capability.
14
PLEX
low Platform experience.
15
LTEX
low Language and tools experience.
16
PCON
nominal Personnel continuity.
17
SITE
nominal Multisite development.
Appendix B: Scale

Factors
Scale factors are new in COCOMO II. They modify second
coefficient in
formula 1 (coefficient
b
). The effect of scale factor is in 1.01  1.26

range. The second column shows factors for this case study project.

Scale
Factor
Sample Project
Value
Description
1
PREC
nominal Precedence.
2
PMAT
CMM Level I (upper) Process maturity.
3
TEAM
nominal Team cohesion.
4
FLEX
nominal Development flexibility.
5
RESL
little (20%)
Architecture and risk
resolution.
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/>License
This article has no explicit license attached to it but
may contain usage
terms in the article text or the download files themselves. If in doubt
please contact the author via the discussion board below.
A list of licenses authors might use can be found here
About the Author
Stan1964


Member

Location: Russian Federation

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Msgs 1 to 11 of 11 (Total in Forum: 11) (Refresh) First Prev Next
inform
boumedian
22:10 23 Apr '06
Re: inform Leonhardt Wille
4:50 2 May '06
Why estimate if the code is
"already" there?
Anonymous
15:05 20 Aug '05
Re: Why estimate if the
code is "already" there?
Stan1964
20:11 20 Aug '05
Re: Why estimate if the
code is "already" there?
blongtq
17:09 16 Jan '06
Commo II and RAD tools Blackboss
9:48 22 May '05
Re: Commo II and RAD

tools
Anonymous
22:33 20 Jun '05
Re: Commo II and RAD
tools
dionisio
2:38 4 Dec '07
Fancy mambo jumbo to
justify cost
Brian Shifrin
10:19 31 Jan '05
Ross' Rule Of Pi
Marc Clifton
1:55 11 Jan '05
Re: Ross' Rule Of Pi Jörgen Sigvardsson
4:18 11 Jan '05
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/>Last Visit: 12:31 13 Nov '09 Last Update: 12:31 13 Nov '09 1
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