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* Property of STI of 10

Software Project Estimation

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Observation on Estimating


Software Sizing

Problem-Based Estimation

Process-Based Estimation

Structure of Estimation Model

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* Property of STIPage 3 of 10


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Variables affecting cost of software and effort:

human technical environment political

Options to achieve reliable cost and effort

estimates: Delay estimation until late in the

project Base estimates on similar projects that

have already been completed Use relatively simple “decomposition

techniques” to generate project cost and effort estimates

Use one or more empirical models for software cost and effort estimation

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Observation on Estimating

Factors affecting Estimation:

Project complexity

Project size

Structural uncertainty

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Software Sizing

Things predicted on software project estimate

accuracy: the degree to which the planner has

properly estimated the size of the product to be built

the ability to translate the size estimate into human effort, calendar time, and money

the degree to which the project plan reflects the abilities of the software team

the stability of product requirements and the environment that supports the software engineering effort

Different approaches to sizing problem: “Fuzzy-logic” sizing Function point sizing Standard component sizing Change sizing

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Problem-Based Estimation

LOC and FP are used in two ways: as an estimation variable that is used to

“size” each element of the software as baseline metrics collected from past

projects and used in conjunction with estimation variables to develop cost and effort projections

When LOC is used as the estimation variable, decomposition is absolutely essential and is often taken to considerable levels of detail.

For FP estimates, each of the information domain characteristics — inputs, outputs, data files, inquiries, and external interfaces are estimated rather than focusing on function.

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Process-Based Estimation

basing the estimate on the process that will be used – the process is decomposed into a relatively small set of tasks and the effort required to complete each task is estimated

starts with a description of software functions acquired from the project scope

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Example of LOC and FP Based Estimation

Estimation table for LOC method

Estimating information domain values

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Structure of Estimation Models

A typical estimation model is derived using regression analysis on data collected from past software projects.

E = A + B x (ev)C

where A, B, and C are empirically derived constants, E is effort in person months, and ev is the estimation variable (either LOC or FP)

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Software Equation

multivariable model that assumes a specific distribution of effort over the life of a software development project

estimation model of the form was derived from productivity data collected for over 4000 contemporary software projects:

E = [LOC x B0.333/P]3 x (1/t4)

where E= effort in person-months or person-

years t = project duration in months or years B= “special skills factor” that

increases slowly as “the need for integration, testing, quality assurance, documentation, and management skills grow”

P= “productivity parameter”

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Automated-Estimation Tools

Generic functions:

Sizing of project deliverables

Selecting project activities

Predicting staffing levels

Predicting software effort

Predicting software cost

Predicting software schedules

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handout 4

Design