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Shashwat Shriparvdwivedishashwat@gmail.comInfinitySoft

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Estimating the cost of a Software product is one of the most difficult and error prone tasks.

Cost estimates can be of two types:1) Top down approach

2) Bottom up approach

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TOP DOWN APPROACH I t focuses on system level cost like computing resources as well as the cost of configuration

management ,quality assurance ,system integration ,training and publications.

I t focuses on system level cost but may overlook

various technical factors.

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BOTTOM UP APPROACH

I t first estimates the cost to develop each module and these cost are combined to arrive at an overall

estimate.

I t emphasizes the cost associated with developing individual system components but fail to account

for system level costs.

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METHODS FOR ESTIMATION

1) Expert Judgment 2) Delphi Cost Estimation

3) Work Breakdown Structures

4) Algorithmic Cost Models

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Compute the estimate cost of the software system as the sum of costs of the modules and the

subsystem that comprises the system.They follow Bottom Up Approach.

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CONSTRUCTIVE COST MODEL

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The following activities are covered by the estimates:

a) Covers estimate through acceptance testing

b) I ncludes the cost of documentation and reviews.

c) I ncludes the cost of Project Manager.

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The cost estimators exclude planning and analysis costs ,installation and training cost and

cost of computer operators , secretaries.The DS I (Delivered Source I nstruction) estimate

includes job control statement and source statements but excludes comments

I t is considered to be one line or card image.

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Following are the assumptions estimated by the

COCOMO concerning the nature of the software:-

1) Careful definition and validation of requirements is performed by a small number of capable people.2) Requirements remain stable throughout the

project 3) Careful definition and validation of architectural

designs is performed by a small number of capable people.

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4) Detailed design ,coding and unit testing are performed in parallel by group of programmers

working in teams.5) I ntegration Testing is based on early test

planning.

6) I nterface errors are found by unit testing and by inspections.

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F ormally there are mainly 10 steps to estimate the cost using COCOMO:-

1) I dentify all the subsystem and modules in the product.

2) Estimate the size of each module and calculate the size of each subsystem and the total system.

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3) Specify the module level multipliers.4) Compute the module effort and the time

estimates for each modules.5) Specify the effort multipliers for each

subsystems.6) F rom Steps 4 and 5 compute the estimated

effort and development time for each subsystems.

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7 ) F rom Step 6 compute the total system effort and development time.

8) Perform sensitivity analysis on the estimate.9) Add other development cost like planning and analysis that are not included in the estimates.

10) Compare this estimate with the one developed by Delphi estimation .I dentify and Rectify the differences in the estimates.

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MODULE LEVEL MULTIPLIERS Product Complexity

Programmers Capability Virtual Machine Experience

Programming Language Experience

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PRODUCT ATTR I BUTES

Required Reliability Data-base Size Product Complexity

COMPUTER ATTR I BUTES

Execution time constraint Main storage Constraint Virtual machine reality

Computer turnaround time

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ADVANTAGES:-o The model can be used to gain insight into the cost

factors.o Systematic techniques of software engineering are

used throughout the development process.o Data can be collected and analyzed ,new factors

can be identified and effort multipliers can be adjusted.

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Shashwat Shriparvdwivedishashwat@gmail.comInfinitySoft