COCOMO

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COCOMO COCOMO 2.0byDeanna B. Legg Barry
Boehm, Bradford Clark, Ellis Horowitz and Chris
Westland1995

• EEL6887 Software Engineering
• Sirisha Budaty
• February 1st 2006

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Reference Sources

• Textbook Software Engineering Project
  Management, 2nd ed., edited by Thayer and
  Yourdon, IEEE Computer Society, 2000.
• pp230 Synopsis of COCOMO", by Deanna B. Legg
• pp270 Cost Modelsfor Future Software Lifecycle
  Processes COCOMO 2.0, by Barry Boehm, Bradford
  Clark, Ellis Horowitz, Chris Westland, Ray
  Madachy and Richard Selby
• Safe and simple software cost analysis, by
  Boehm, B., Software, IEEEVolume 17,  Issue 5, 
  Sept.-Oct. 2000 Page(s)14 17, Digital Object
  Identifier 10.1109/52.877854
• http//softstarsystems.com/cocomo2.htm
• http//sunset.usc.edu/research/COCOMOII/Docs/mode
  lman.pdf

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What is COCOMO ?

• COCOMO COnstructive COst MOdel
• A software cost estimation method that is based
  on a set of empirically derived equations. The
  equations incorporate a number of variables
  considered to be the major cost drivers of
  software development and maintenance.
• It is based on the classical waterfall model of
  the software life cycle.
• System Feasibility
• Software Plans and Requirements
• Software Design
• Programming
• Integration and Test
• Implementation
• Maintenance

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Waterfall Model of Software life cycle
COCOMO provides effort estimation for the
development phase only.
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Definitions and Assumptions

• DSI (Delivered Source Instructions) is the
  primary cost driver. The term delivered
  excludes non-delivered support software.
• PM (Person-Month) A COCOMO person-month
  consists of 19 days(152hrs) of working time
  (including the average time off due to sick
  leave, holidays, and vacation).
• The development period covered by COCOMO cost
  estimates start at the beginning of the software
  design phase and ends at the end of the
  integration and test phase.
• COCOMO estimates assume that the project will be
  managed well by both the developer and the
  customer.
• COCOMO estimates assume that the requirements
  specification does not significantly change after
  the plans and requirements phase.
• COCOMO should not be used for projects below 2000
  DSI, since differences in personnel will tend to
  dominate all other effects.

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Versions of COCOMO

• Basic, used mostly for rough early estimates.
• Intermediate, is the most commonly used version.
• - Incorporates 15 cost drivers to account for
  software project cost variations that are not
  directly related to project size (i.e., personnel
  capability, use of modern tools, hardware
  constraints etc)
• Detailed, Not used very often
• - accounts for the influence of the different
  factors on individual project phases..
• Development Types
• Organic Type
• Relatively small software teams develop familiar
  types of software in an in-house environment.
• Most of the personnel connected with the project
  have previous experience working with related or
  similar systems in the organizations.
• Embedded Type
• Project may require new technology, unfamiliar
  algorithms or an innovative new method of solving
  a problem.
• Semi-detached Type
• An intermediate stage between organic and
  embedded types (i.e., either a mixture of organic
  and embedded type or an intermediate level of the
  project characteristics).

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Cost Estimation using Basic COCOMO

• Type Effort Schedule
• Organic PM 2.4 (KDSI)1.05 TD 2.5 (PM)0.38
• Semi-Detached PM 3.0 (KDSI)1.12 TD 2.5
  (PM)0.35
• Embedded PM 3.6 (KDSI)1.20 TD 2.5 (PM)0.32
• - PM person-month
• KDSI delivered source instructions, in
  thousands
• TD number of months estimated for software
  development
• EXAMPLE
• Assumption
• Organic Project with estimated size of 128,000
  lines of code.
• Effort PM 2.4 (128)1.05 392 person-months
• Productivity 128,000 DSI/392 PM 327 DSI/PM
• Schedule TD 2.5 (392)0.38 24 months
• Avg. Staffing 392 PM/ 24 months 16 PM/TD

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Cost Estimation using Intermediate COCOMO

• It is a compatible extension to basic COCOMO.
• It provides great accuracy and level of detail
  which makes it more suitable for cost estimations
  in the more detailed stages of software product
  definition.
• The intermediate COCOMO exponents for the three
  software development types are the same as Basic
  COCOMO, but the coefficients are different. The
  Intermediate development schedule is determined
  using the Basic COCOMO schedule equations.
• Type Effort Schedule
• Organic PM 3.2 (KDSI)1.05 TD 2.5 (PM)0.38
• Semi-Detached PM 3.0 (KDSI)1.12 TD 2.5
  (PM)0.35
• Embedded PM 2.8 (KDSI)1.20 TD 2.5 (PM)0.32

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Cost Drivers

• Intermediate COCOMO incorporates 15 predictor
  variables called Cost Drivers
• These are grouped into 4 categories

• - Software Attributes
• Required Software Reliability (RELY)
• Data Base Size (DATA)
• Software Complexity (CPLX)
• - Personnel Attributes
• Analyst Capability (ACAP)
• Applications Experience (AEXP)
• Programmer Capability (PCAP)
• Virtual Machine Experience (VEXP)
• Programming Language Experience (LEXP)

• - Computer Attributes
• Execution Time Constraint (TIME)
• Main Storage Constraint (STOR)
• Virtual Machine Volatility (VIRT)
• Computer Turnaround Time (TURN)
• - Project Attributes
• Use of Modern Programming Practices (MODP)
• Use of Software Tools (TOOL)
• Schedule Constraint (SCED)

Text pp-240 effort calculation chart
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COCOMO 2.0

• COCOMO failed to estimate cost for the new
  processes which include
• Non-sequential and rapid-development process
  model
• Reuse and re-engineering driven approaches
• Object-oriented approaches
• Software process maturity initiatives
• Changes in scaling effects
• Changes in cost drivers
• COCOMO 2.0 was successful in addressing these
  issues
• COCOMO 2.0 is tuned to modern software life
  cycles.
• COCOMO 2.0 targets the software projects of the
  1990s and 2000s.

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COCOMO 2.0 Objectives

• To develop a software cost and schedule
  estimation model tuned to the life cycle
  practices of the 1990s and 2000s
• To develop software cost database and tool
  support capabilities for continuous model
  improvement
• To provide a quantitative analytic framework
• These objective support
• Project Planning and scheduling
• Project staffing
• Estimates-to-complete
• Project preparation
• Preplanning and rescheduling
• Project tracking
• Contract negotiation
• Proposal evaluation
• Resource leveling
• Concept exploration
• Design evaluation and
• Bid/on-bid decisions

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COCOMO 2.0 Models

• Suitable for projects built with modern
  GUI-builder tools.
• Based on new Object Points.

• Suitable to get rough estimates of a project's
  cost and duration before its entire architecture
  is determined.

• Used after the projects overall architecture is
  developed.

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COCOMO 2.0 Cost Factors Sizing

• COCOMO 2 Sizing quantities
• Object Points
• Function Points
• Object Point Estimation Procedure
• Estimates the effort involved in Application
  Composition and prototyping projects.
• Definitions of terms
• NOP New Object Points
• srvr number of server/mainframe data tables
  used in conjunction with the screen or Report
• Clnt number of client/personal workstation data
  tables used in conjunction with the Screen and
  Report
• reuse the percentage of screens, reports, and
  3GL modules reused from previous applications.
• OBJECT in Object Points defines screens,
  reports, and 3GL modules as objects.

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Object Point Estimation Procedure
Algorithm

• Step1 Assess Object-Counts by estimating the
  number of screens, reports and 3GL components of
  an application.
• Step2 Classify each object instances into
  simple, medium and difficult
• Step3 Weight the number in each cell using the
  following schema

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Object Point Estimation Procedure contd.

• Step4 Determine object point by adding all the
  weighted object instances.
• Step5 Compute NOP (Object-Points) (100 -
  reuse)/100.
• Step6 Compute Estimated Person-Month
• This process of person-month calculation is
  followed for the entire software application and
  for each of the components comprising that
  application.

PM NOP / PROD
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Cost Estimation using Object Points

• For each component and for the entire software,
  estimate the average man-power cost (K/PM)
• Compute the dollar cost for each component and
  for the entire software as a whole using the
  following formula
• Add up the software development costs of the
  components and compare it with the cost of the
  entire software application already obtained.
• If the difference between the two costs is
  greater than a certain threshold, the whole
  process is redone.

K PM (K / PM)
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Function Points

• COCOMO 2.0 model uses Function Points as the
  basic for measuring size for the Early Design
  stage.

Please refer Presentation Slides of Software
System Size Estimation by Shamik Sengupta.
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COCOMO 2.0 Reuse Model

• COCOMO 2.0 reuse model is different from original
  COCOMO
• ESLOC Equivalent source lines of code
• ASLOC adapted source lines of code
• DM percentage of design modification
• CM percentage of code modification
• IM percentage of original integration effort
  required for integrating the reused software.
• AA percentage of reuse effort due to Assessment
  and Assimilation
• SU percentage of reuse effort due to Software
  Understanding

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COCOMO 2 Cost Factors Scaling

• Software cost estimation models often have
  exponential factor to account for the relative
  economies or diseconomies of scale encountered as
  a software project increase its size.
• Effort A (Size)B
• The value of coefficient A is provisionally set
  at 3.0 for COCOMO 2.0
• The scaling factor (B) adds two factors
  precedentedness and flexibility, to account for
  the mode effects in the original COCOMO.
• Also adds Team Cohesiveness factor to account for
  the diseconomy-of-scale effects on software
  projects.
• A projects numerical ratings Wi are summed
  across all the factors, and used to determine a
  scale exponent B
• B 0.91 0.01 Sum (Wi)

From Ref4
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Tools

• Leading COCOMO 2.0 based Software Cost-Estimation
  Tools
• These URLs provide descriptions of leading
  software cost-estimation tools. Each tool cited
  has been backed by a lot of effort to relate the
  tool to a wide variety of software project
  experiences.
• COSTAR (Softstar Systems) www.softstarsystems.com
  
• - Software project managers use Costar to produce
  estimates of a project's duration, staffing
  levels, effort, and cost .
• CostXpert (Marotz, Inc.) www.costxpert.com
• Cost Xpert is a cost estimating software
  development process tool.
• COCOTS is a model complementary to COCOMO 2.0

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Summary

• Software cost estimation
• Performed at the beginning of the projects
• performed by project managers
• Project manager should go through extensive
  training
• Methods to support cost estimation
• basic COCOMO
• Intermediate COCOMO
• COCOMO 2.0
• COCOMO 2.0 more successful for processes tuned to
  the life cycle practices of the 1990s and 2000s
• Cost estimation method supported by COCOMO 2.0
  applies directly to CMM level 2