Kuliah 3- Estimation.pdf

8/18/2019 Kuliah 3- Estimation.pdf

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Estimation

Eddy Gunawan, S.T.P, M.T.I


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What is estimation?The project manager must set expectations

about the time required to complete thesoftware among the stakeholders, the team,and the organization’s management.

http://www.stellman-greene.com2

ose expec a ons are no rea s c rom ebeginning of the project, the stakeholders willnot trust the team or the project manager.


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Estimation AccuracyDefinition phase

50-100% inaccurateAnalysis PhaseAccuracy of the estimation is double

-Design

About 10% inaccurate


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Elements of a Sound EstimateTo generate a sound estimate, a projectmanager must have:

A work breakdown structure (WBS), or a list of taskswhich, if completed, will produce the final productAn effort estimate for each task


A list of assumptions which were necessary formaking the estimateConsensus among the project team that theestimate is accurate


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Assumptions Make Estimates MoreAccurate

Team members make assumptions about thework to be done in order to deal withincomplete information

Any time an estimate must be based on a decisionthat has not yet been made, team members canassume the answer for the sake of the estimate


Assumptions must be written down so that if theyprove to be incorrect and cause the estimate to beinaccurate, everyone understands what happenedAssumptions bring the team together very early onin the project so they can make progress onimportant decisions that will affect development


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Estimation Joke


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Work Breakdown StructuresThe key to any plan is breaking the requiredactivities into smaller and smaller pieces.A WBS begins by listing the major components ofthe project.

breaking the project up into the major pieces is tostart with phases of software developmentLower levels of the WBS are obtained bybreaking down each piece at the level above intoits component activities


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WBS Numbering SystemLevel 0 or project title, is 0.0

Each level 1 item is N.0 , ex: 1.0 , 2.0 etcEach level 2 item below level 1 item N.0 isnumbered N.1, N.2, etc.


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WBS Numbering System Example


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When Do You Stop?The lowest level entries are the tasks, or activitiesin the project. You can stop breaking down a taskif the following is true :

1. Some person (or group for a larger project) cantake responsibility for the task.

2. You can get a rough estimate of the effortneeded to perform the activity involved.3. You can schedule the task. Calender duration

and its precedents is clear.4. The task must be small and able to be

completed


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WBS with estimation example


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WBS for Software ImplementationProject


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WBS for Software ImplementationProject (cont’)


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WBS for Software ImplementationProject (cont’)


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WBS for Web Design Project


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WBS for Web Design Project (cont’)


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WBS for Web Design Project (cont’)


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Estimation techniques

Use of professional judgment

Use of historyUse of formulas


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Wideband Delphi Wideband Delphi is a process that a team canuse to generate an estimate

The project manager chooses an estimation team,and gains consensus among that team on theresults


because it consists of a straightforward set of stepsthat can be performed the same way each time


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The Wideband Delphi ProcessStep 1: Choose the team

The project manager selects the estimation teamand a moderator. The team should consist of 3 to 7project team members.

The moderator should be familiar with the Delphi process,but should not have a stake in the outcome of the session if


possible.If possible, the project manager should not be themoderator because he should ideally be part of theestimation team.


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The Wideband Delphi ProcessStep 2: Kickoff Meeting

The project manager must make sure that eachteam member understands the Delphi process, hasread the vision and scope document and any otherdocumentation, and is familiar with the project


background and needs.The team brainstorms and writes downassumptions.The team generates a WBS with 10-20 tasks.The team agrees on a unit of estimation.


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The Wideband Delphi ProcessStep 3: Individual Preparation

Each team member independently generates a setof preparation results.For each task, the team member writes down anestimate for the effort re uired to com lete the task,


and any additional assumptions he needed to makein order to generate the estimate.


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Individual Preparation result


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The Wideband Delphi ProcessStep 4: Estimation Session

During the estimation session, the team comes to aconsensus on the effort required for each task in theWBS.Each team member fills out an estimation form


which contains his estimates.The rest of the estimation session is divided intorounds during which each estimation team memberrevises her estimates based on a group discussion.Individual numbers are not dicsussed.


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The Wideband Delphi Process

Step 4: Estimation Session (continued)The moderator collects the estimation forms andplots the sum of the effort from each form on a line:

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The Wideband Delphi ProcessStep 4: Estimation Session (continued)

The team resolves any issues or disagreements that are brought up.Individual estimate times are not discussed. These disagreements areusually about the tasks themselves. Disagreements are often resolved byadding assumptions.

The estimators all revise their individual estimates. The moderatorupdates the plot with the new total:

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The Wideband Delphi ProcessStep 4: Estimation Session (continued):

The moderator leads the team through several rounds of

estimates to gain consensus on the estimates. The estimationsession continues until the estimates converge or the team isunwilling to revise estimates.

Step 5: Assemble Tasks


The project manager works with the team to collect theestimates from the team members at the end of the meetingand compiles the final task list, estimates and assumptions.

Step 6: Review ResultsThe project manager reviews the final task list with theestimation team.


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Other Estimation TechniquesPROBE, or Proxy Based Estimating

PROBE is based on the idea that if an engineer is building acomponent similar to one he built previously, then it will take about

the same effort as it did in the past.Individual engineers use a database to maintain a history of the effortthey have put into their past projects.A formula based on linear regression is used to calculate the estimatefor each task from this history.


COCOMO IIIn Constructive Cost Model, or COCOMO, projects are summarizedusing a set of variables that must be provided as input for a modelthat is based on the results of a large number of projects across theindustry.The output of the model is a set of size and effort estimates that can

be developed into a project schedule.


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COCOMO VersionsCO (Constructive) CO (Cost) MO (Model)First version: 1981 by Dr. Barry Boehm

Now known now as “COCOMO 81”

Second version: ADA Cocomo (ADA 87);parameterized exponent reflecting moremodern practices and their economies of

scale.Current Version: Cocomo II (circa 2000)Regression formula, with data taken fromhistorical projects and current projectcharacteristics.

ocomo :


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ocomo :Limitations as years progressed

Software reuse

Application generation programsObject oriented approaches

,translation)Rapid development


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Other Estimation TechniquesThe Planning Game

The Planning Game is the software project planning methodfrom Extreme Programming (XP), a lightweight developmentmethodology developed by Kent Beck in the 1990s atChrysler.It is a full planning process that combines estimation withidentifying the scope of the project and the tasks required to


.

The Planning Game is highly iterative. The scope isestablished by having Development and Business worktogether to interactively write “user stories” written on indexcards to describe the scope. Each story is given an estimate of1, 2 or 3 weeks. This process is repeated continuouslythroughout the project.


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Estimating ProgrammingOne formula approach that has been verysuccessful for estimating the programming phaseis a simplified function point approach

D = C x (G + J)

Where :D is the task durationC is the complexity factorG is the general experience factorJ is the job knowledge factor


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Complexity factorTo derive complexity factor of a task :

Break it down to smallest posible repeatable functionswithin taskAdd up the complexity of each function (function points)

Function points :User input

User displayPeripheral I/ORestructuring dataCondition checkingCalculationBranchingCalling


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Weighting Factors for ProgramComplexity


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Weighting Factors for ProgramComplexity (cont’)


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Productivity FactorsProductivity is influence by :

General years of experienceknowledge of the jobInterest level

Etc


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Factors for Job Knowledge (J)


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ExampleLet us estimate how long it would take to write a particularPASCAL program. The numbers in parenthesis arereferences to lines in the calculation below.(1)T'he program prompts the user for something, (2)readsthe user response,(3)validates it, (4)reads a record from disk. (5)calculates a

,

back to disk, (7)displays the result to the user, and (8)callsanother module (returns).(9)The programmer has two years of experience, is a goodbut average programmerwho has (10)fair knowledge of this particular application,but no knowledge of relatedapplications. (1 1)Some job knowledge is needed to do this

job.


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Function Factor

(1) User display (simple) 2

(2) User input (simple) 2(3) Condition checking (complex) 4

(4) Peripheral input (simple) 4

a cu a on s mp e

(6) Peripheral output (simple) 4

(7) User display (simple) 2

(8) Calling (simple) 3

Total Complexity 23


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General experience G(9) Programmer is average (2 yrs. Exp) G=1.00

Job knowledge J(10) Fair knowledge of application, no knowledge,

= .

Plugging all this into Formula :Duration = 23 x (1.00 + 0.75) = 40.25 person days

It will take particular person 40 days to design,document, code an test this program


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Estimating The Analysis PhaseEstimating analysis is very difficult because it issuch a human oriented activity.


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Analysis Estimating Worksheet

l k h


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Analysis Estimating Worksheet

(cont’)


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Example of Estimating Analysis

E l f E i i A l i


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Example of Estimating Analysis

(cont’)


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Ratio


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Estimating Rule of ThumbNever ask an inexperienced person to estimateEstimate in a group if you can afford themanpowerNever force an estimate on a professional suchas programmer

Never take an average of different estimatesGranularize down to one week or lessAlways add for contingencyAlways quote a range when giving estimates tomanagers or clientUse your ‘gut feel’


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ReferenceAndrew Stellman dan Jennifer Greene (2005),Applied Software Project Management, Edisi ke-1, O’Reilly Media Inc.2. John J. Rakos (1990), Software Project

,

Prentice Hall.


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Tugas 2Melanjutkan tugas 1, dari vision, scope danproject plan dari tugas 1, buatlah :

1. Work breakdown structure project2. Estimasi project

Tugas dikumpulkan pada perkuliahan berikutnya.

Kuliah 3- Estimation.pdf

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