Презентация на тему Software metrics using constructive cost model

and indirect .
Function points as indirect metrics .
Function points

are used to measure the effort of the project
Cost estimation model

Introduction

estimation ?

How are they calculated ?

effort and schedule of a project .
Cost estimation models

give easy ways for risk mitigation and prepare plan for building the project .
They are calculated using cost drivers .
What are cost drivers ?
Cost drivers are critical features that have a direct impact on the project.

the year 1981.
It is an algorithmic cost model.
It is

based on size of the project.
The size of the project may vary depending upon the function points .

CONSTRUCTIVE COST MODEL

.
team size is considered to be small.
Cost drivers

depend upon size of the projects .
Effort E = a * (KDSI) b * EAF Where KDSI is number of thousands of delivered source instructions a and b are constants, may vary depending on size of the project .
schedule S= c * (E) d where E is the Effort and c, d are constants.
EAF is called Effort Adjustment Factor which is 1 for basic cocomo , this value may vary from 1 to 15.

COCOMO MODELS

developed in familiar environment.
There is a proper interaction among

the team members and they coordinate their work.
Bohem observed E=2.4(KDSI)1.05 E in person-months.
And S=2.5(E)0.38.

Classes of software projects

embedded mode in terms of team size.
It consists of

experienced and inexperienced staff.
Team members are unfamiliar with the system under development.
Bohem observed E=3(KDSI)1.12 E in person-months.
S.35=2.5(E)0And

are highly skilled.
Team members are familiar with the

system under development.
Bohem observed E=3.6(KDSI)1.20 E in person-months.
And S=2.5(E)0.32.
 

cost drivers are intermediate to basic and advanced cocomo.
Cost

drivers depend upon product reliability, database size, execution and storage.
Team size is medium.

Advanced COCOMO
It is used for large sized projects.
The cost drivers depend upon requirements, analysis, design, testing and maintenance.
Team size is large.

schedule of the project, starting from the design phase

and till the end of integration phase. For the remaining phases a separate estimation model should be used.
COCOMO is not a perfect realistic model. Assumptions made at the beginning may vary as time progresses in developing the project.
When need arises to revise the cost of the project. A new estimate may show over budget or under budget for the project. This may lead to a partial development of the system, excluding certain requirements.
COCOMO assumes that the requirements are constant throughout the development of the project; any changes in the requirements are not accommodated for calculation of cost of the project.
There is not much difference between basic and intermediate COCOMO, except during the maintenance and development of the software project.
COCOMO is not suitable for non-sequential ,rapid development, reengineering ,reuse cases models.

LIMITATIONS OF COCOMO

in the requirements, staff size, and environment in which

the software is being developed.
The calculation for cost estimation accuracy is given as follows
Absolute error= (Epred - Eactual)
Percentage error= (Epred - Eactual)/Eactual
Relative error= 1/n ∑ (Epred - Eactual)/Eactual
The above results give a more accurate estimation of costs for future projects.The cost estimation model now becomes more realistic .

COST ESTIMATION ACCURACY

limitations of calculating the costs for non-sequential, rapid development,

reengineering and reuse models of software.
It has 3 modules
Application composition: - good for projects with GUI interface for rapid development of project.
Early design: - Prepare a rough picture of what is to be designed. Done before the architecture is designed.
Post architecture: - Prepared after the architecture has been designed.  

COCOMO II

replaced by 5 scale factors.
Effort (E) is calculated

as follows
E = a * (KDSI) sf * π (EM)
Where a is constant, sf is scaling factor, EM is Effort Multiplier (7 for Early design, 17 for Post architecture).

COCOMO II calculation

financial calculations of the project.
Establishes the cost and schedule

of the project under development, this provides a plan for the project.
Provides a more reliable cost and schedule, hence the risk mitigation is easy to accomplish.
It overcomes the problem of reengineering and reuse of software modules.
Develops a process at each level . Hence takes care of the capability maturity model.

COCOMO II USES

Boehm, is the most common and widely used cost

estimation models for most software projects.
The effort and schedule calculated by the model is based on two things, historical information and experience. Thus the reliability on cocomo has been increased.
The website provided by NASA on cocomo, provides a cocomo calculator with cost drivers for a complex project. Cost drivers directly have an impact on the development of the project.

CONCLUSION

http://www2.enel.ucalgary.ca/People/Smith/619.94/prev689/1997.94/reports/farshad.htm
[2]IAN SOMMERVILLE,”

Software Engineering”, published by addision wesley, pg 514- 521.
[3]Seth Bowen, Samuel Lee, Lance Titchkosky,”Software cost estimation”,
http://www.computing.dcu.ie/~renaat/ca421/BLTCostEst.ppt

[4]Barry Boehm, “Cost Estimation With COCOMO II”, http://sunset.usc.edu/classes/cs577a_2002/lectures/19/ec19.pdf
 
[5]Center for Systems and Software engineering, “COCOMO II”, http://sunset.usc.edu/csse/research/COCOMOII/cocomo_main.html.

References