brief explanation of software development projects / products cocomo stages classification examples

1. COCOMO
Constructive Cost Estimation Model
Harshdeep Singh
M.Tech(CE)-PT
11471011

2. Definition
• Predicts the effort and schedule for a software
development projects.
• Based upon inputs:
– Size of the software(KLOC).
– Number of cost drivers
that affect productivity.

3. Class. of S/w Development Projects
• COCOMO was developed by Barry Boehm in 1981
• Barry postulated that any Software Development
Project can be classified on the development
complexity
• Three categories :
– Organic Type
– Semi-detached Type
– Embedded Type

4. Organic
• Development project can be considered of organic
type :
– The project is developed in a familiar, stable
environment
– Size of the development team is reasonably small
– The team members are experienced in developing
similar types of projects.

5. Semi-detached
– Development consists of a mixture of experienced
and inexperienced staff.
– Team members may have limited experience on
related systems
– Unfamiliar with some aspects of the system being
developed

6. Embedded
– Project which is complex in nature
– Eg1. software being developed is strongly coupled
to complex hardware
– Eg2. project characterized by inflexible constraints
and interface requirements.
– An embedded mode project will require a great
deal of innovation.
– Air traffic control system

7. Some assumptions
• Primary cost driver is the Delivered Line Of Code
(LOC)
• COCOMO estimates assume that the project will
enjoy good management by both the developer and
the customer
• Assumes the requirements specification is not
substantially changed after the plans and
requirements phase

8. Stages of COCOMO
• Basic COCOMO
• Intermediate COCOMO
• Complete/Detailed COCOMO

9. Basic COCOMO
• Basic COCOMO is good for quick, early, rough order
of magnitude estimates of software costs(EFFORT &
SCHEDULE)
• Gives a approx. estimate of project parameters

10. Cont..
The basic COCOMO estimation model is given by the
following expressions:
Effort = a1 х (KLOC)a2 PM
Tdev = b1 x (Effort)b2 Months
Where
• KLOC is Kilo Lines of Code (size of project),
• a1, a2, b1, b2 are constants for each category of project,
• Tdev is the estimated time to develop the software,
• Effort expressed in person months (PMs).

11. Person-Month
10 persons should work for 1 month
1 person should be employed for 10 months
•The effort estimation is expressed in units of person-
months (PM).
•It should be carefully noted that an effort of 10 PM
does not imply
•What it means :
 10 person effort typically in 10
months

12. Person-month curve
• person-months (PM) denoted by the area under the
person-month curve

13. Constants of projects
• The values of a1, a2, b1, b2 for different categories of
products :

14. Example
• We have determined our project fits the characteristics
of Semi-Detached mode
• We estimate our project will have 32,000 Delivered
Source Instructions.
• Using the formulas, we can estimate:
– Effort = 3.0*(32)^1.12 = 146 PM
– Schedule = 2.5*(146) ^0.35 = 14 months
– Cost required = 146*15000 = Rs.2,19,000 -
– Average Staffing = 146 PM /14 months = 10

15. Limitation
• Its accuracy is necessarily limited because of its lack
of factors which have a significant influence on
software costs :
– Hardware constraints
– Use of modern tools and techniques. etc
• Assumption that the entire project cost is incurred on
account of the manpower cost alone.

16. Intermediate COCOMO
• Basic COCOMO model assumes that effort and
development time are functions of the
product size alone
• The intermediate COCOMO model refines the
initial estimate obtained using the basic
COCOMO by using a set of 15 cost drivers

17. Cost attributes
• The cost drivers are grouped into four categories :
– Software Product Attributes
– Computer Attributes
– Personnel Attributes
– Project Attributes

18. Cost attributes

19. Cont..
• Consider in expression by term “Effort Adjustment
Factor” (EAF).
• The intermediate Cocomo takes the form.
– E=a1(KLOC)^a2*EAF
• where E:Effort
• KLOC : Kilo lines of code
• EAF : It is the effort adjustment factor

20. Complete/Detailed COCOMO
• Major shortcoming of both the basic and
intermediate COCOMO models is that they consider
a software product as a single homogeneous entity.
• For example, some sub-systems may be considered
as organic type, some semidetached, and some
embedded.
• This approach reduces the margin of error in the final
estimate.

21. Example
• A distributed Management Information System (MIS)
product for an organization have the following sub-
components:
– Database part
– Graphical User Interface (GUI) part
– Communication part
• The costs for these three components can be estimated
separately, and summed up to give the overall cost of the
system

22. Thank You