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Software Quality ManagementModule 6

K. MohananResearch Scholar, CUSAT

(Scientist E, NPOL)

Software Quality ManagementModule 7K. MohananResearch Scholar, CUSAT

(Scientist E, NPOL)

SOFTWARE PROJECT

COST ESTIMATION

Akhil ChandranLecturer in IT

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02 / 12Software Project Management (SPM)

Major Issues in

Software Cost Estimation

Companies and/or Projects do not collect Project Cost Data on past projects

Precision of estimate is far greater than its accuracy

Estimates are usually based on LOC, which itself is an estimate

Software cost estimates are hard to justify

Cost models are not perceived to be very reliable.therefore, they are not used with any degree of regularity.

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03 / 12Software Project Management (SPM)

Why are Software Estimations so unreliable ?

Lack of historical data from past projects.

First-of-a-kind system. Past history on similar projects do not exist.

Lack of expertise by the estimator in making estimates.

Things left out. There are often large pieces that just never get put on thelist of things to do; and they are discovered later

Premature Estimation. Estimates must be given before a proper understandingof the project is available or developed.

Productive time is not 40 hours per week, yet many schedules are built as if itwere.

Failure to update estimates when the project or environment changes.

Undue optimism on the part of the developers.

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04 / 12Software Project Management (SPM)

Cost estimation techniques

Algorithmic Models :Algorithms for producing a software cost estimate. Eg. COCOMO

Rules of thumb :Guidelines that have evolved over time

Expert Judgment :Consulting one or more experts. Eg. Dephi Technique

Estimation by Analogy :Comparisons with completed projects

Design to cost :Product is matched to the cost available.

Price-to-win estimating :Price believed to be necessary to win the job (not a cost estimate)

Top-Down Estimating :Overall estimate derived from global properties. Eg. Intrmedt COCOMO

Bottom-Up Estimating :Each component is separately estimated and the results aggregated

(WBS is a useful tool for this).

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05 / 12Software Project Management (SPM)

Software Cost Estimation

Two basic classes of Estimates

Experience based may be flawed due to obsolescence of the historical data used estimators memories of the past data are flawed

Parameter based Parametric models typically have a perspective. Some clearly fit a military std dev process. Eg. MIL-STD-498 Some others fit commercial dev procedures Estimators must choose models suited to their project environment.

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06 / 12Software Project Management (SPM)

COCOMO

COnstructive COst estimation MOdel. Software cost estimation method that is based ona set of empirically derived equations.

SystemFeasibility

S/w Plans &Reqmnts

SoftwareDesign

Programming

Integration& Test

Implementation

Maintenance

Waterfall model of the software life cycle

Separate Estimation

No coverage

COCOMO coverage

Installation

Plans,

Activities,Training

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08 / 12Software Project Management (SPM)

COCOMO : 3 Development types

Organic Relatively small software teams Familiar types of software In-house environment

Project personnel have previous experience

Semi-detached Between organic and embedded

Intermediate level of project characteristics or mix of organic andembedded

Embedded

New technology Unfamiliar algorithms Innovative new method of solving a problem. need to operate within tight constraints

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09 / 12Software Project Management (SPM)

COCOMO versions

Three Versions of COCOMO

Basic For rough early estimates.

Intermediate Most commonly used version. 15 different factors to account for.

Detailed (Complete) Accounts for different factors on individual project phases. Not used very often.

Ada COCOMO Includes Incremental Software Development

COCOMO 2.0 Includes Object Points Includes Object-Oriented Development, COTS etc.

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10 / 12Software Project Management (SPM)

Basic COCOMO

Type Effort ScheduleOrganic PM = 2.4 (KDSI) TD = 2.5 (PM)

Semi-Detached PM = 3.0 (KDSI) TD = 2.5 (PM)

Embedded PM = 3.6 (KDSI) TD = 2.5 (PM)

1.05

1.12

1.20

0.38

0.35

0.32

PM = Person Month

KDSI = Delivered Source Instructionsin Thousands

ORKLOC = Lines of Code in Thousands

TD = No of months estimated for

Software DevelopmentExample :

Organic Project. Estimated size 1,28,000 DSI.

Semi-detached Project. Estimated size 1,28,000 DSI.

Embedded Project. Estimated size 1,28,000 DSI.

Effort = PM = 2.4 (128) raised to 1.05 = 392 person months.Productivity = 1,28,000 DSI / 392 PM = 327 DSI / PMSchedule TD = 2.5 (392) raised to 0.38 = 24 Months

Avg Staffing = 392 PM / 24 Months = 16 FSP (Full-time-equivalent Staff Personnel)

Effort = PM = 3.0 (128) raised to 1.12 = 687 person months.Productivity = 1,28,000 DSI / 687 PM = 186 DSI / PMSchedule TD = 2.5 (687) raised to 0.35 = 25 MonthsAvg Staffing = 687 PM / 25 Months = 27 FSP (Full-time-equivalent Staff Personnel)

Effort = PM = 3.6 (128) raised to 1.20 = 1216 person months.Productivity = 1,28,000 DSI / 1216 PM = 105 DSI / PMSchedule TD = 2.5 (1216) raised to 0.32 = 24 MonthsAvg Staffing = 1216 PM / 24 Months = 51 FSP (Full-time-equivalent Staff Personnel)

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Basic COCOMO for Maintenance

Example :Organic Project. Estimated size 1,28,000 DSI, Development effort 392 PM.Assume project had 8000 DSI added and 3400 DSI modified during its first year of maintenance.

ACT = (8000 + 3400) / 128000 = 0.09

Annual maintenance effort = (PM)AM = (0.09)(392) = 35 PMThe number of FSP required to maintain the software is

(FSP)M = 35/12 = 3 FSP.

Definition :S/w maintenance is defined as the modification of existing softwarewhile leaving its primary functions intact

Assumption :The definition does not include major redesign and redevelopment

resulting in greater than 50 percent new code.COCOMO estimate for Annual Software Maintenance:Annual Change Traffic (ACT) :

Defined as the fraction of the software products source instructionswhich undergoes change during a typical year. The changes maybe through addition or modification.

COCOMO maintenance equations are :ACT = (Added DSI + Modified DSI) / Total DSI(PM)AM = (ACT) (PM)DEV

(FSP)M = (PM)AM / 12

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Intermediate COCOMO

Basic COCOMO assumes that effort and dvpmnt time are funs of the productsize alone.

but there are some other parameters besides the product size thataffects effort and devpmnt time.

Intermediate COCOMO consider these parameters also Uses 15 cost drivers (multipliers) for cost estimation. For e.g., if modern pgming practices are used, initial estimates arescaled down by multiplying with a cost driver having a value less that 1.

if there are stringent reliablity reqs, initial estimates are scaledupwards.

Rate these15 cost drivers for a particular pjt on a scale of 1 to 3.

Depending on these ratings , pjt manager suggests appropriate cost drivervalues. i.e., multipliers of the initial estimates by basic COCOMO.

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Intermediate COCOMO

Cost drivers may be from the following items.

1) ProductProduct characteristics include

inherent complexity of the product, reliability reqs of the product, etc.

2) ComputerComputer characteristics include execution speed reqd, storage space reqd, etc.

3) PersonnelPersonnel characteristics include

experience level of personnel, programming capability, analysiscapability, etc.

4) Development environmentAvailability of CASE tools, etc.

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