the art and science of estimating software development cost glenn briskin partner, sierra systems...
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The Art and Science of Estimating Software Development Cost
Glenn BriskinPartner, Sierra Systems Group
A. Nicklas MalikTechnical Architect
Certified Function Point Specialist
Agenda Sierra Systems Intro Estimating Software Development Project Management Point of View
– Key concepts for creating and managing estimates Technical Architect Point of View
– Estimating Size (using Function Points)– Estimating Cost (using Historical Data)
Sierra Systems Intro A full service systems integration company Emphasis on business solutions Over 900 consultants, 300 in PNW
– Vancouver and Victoria– Bellevue and Olympia
Olympia office since 2000 serving over 25 state agencies EGovernment, Health, Justice, Enterprise Solutions Strong methodology and technology expertise
Managing Estimates What’s an estimate? What goes into an estimate? What happens once you make an estimate? How can you make it work for you, not against you?
What’s an Estimate? An estimate predicts what something will cost and how long
it will take to deliver– Numbers– Confidence Level
What goes into an Estimate? Your understanding about what you want Your experience in doing that before The more you know about each, the easier it will be to
estimate
Understanding and Experience Understanding
– What problem will be solved? (Objectives)– What capabilities will solve it? (Functionality)– How will you do it? (Tasks)– What assumptions and constraints do you have?
Understanding and Experience Experience
– What has it taken for you or others to do this?– What historical information do you have?– What expert experience can you draw on?– What is your confidence level in the applicability of your
information?– What do you know about your possible resources?
Estimating Process
Functionality
Tasks/Resources
History
Assumptions and Constraints
Estimating Tools and Processes
Estimates of Costs and
Time
Confidence Level
How much of this comprises your estimate?
Functionality
Tasks/Resources
History
Assumptions and Constraints
Estimating Tools and Processes
Estimates of Costs and
Time
All of it!
Confidence Level
What Happens when you make an Estimate?
Set expectations– Cost, Time, Scope– People see what they are looking for
Create a baseline– Cost, Time, Scope– Assumptions, Constraints, Confidence
Making the Estimate Work for You
When any part of the estimate changes…– Functionality– Tasks– Assumptions/Constraints– Cost and Time Estimates– Confidence Level
Then the entire estimate has changed Adjust expectations and show variance to the baseline Negotiate changes to expectations
Estimating Models – A case for Function Points
‘And then magic happens…’ Your inputs vary in quality and completeness Characteristics of a useful estimating model
– Consistently applied to the information available– Usable early with accuracy– Easily updateable – responsive to changes– Applicable to historical projects– Adjustable with experience
Estimating Tools and Processes
Top down vs. Bottom Up
Project charter
Iteration PlanHigh Level
RequirementsProject
Planning Detailed
Project Plan
Determine size
Calc. Cost Estimate
Historicaldata
Determine tasks
Estimate task durations
Experience
Assign resources
Calc. Cost Estimate
Top-downestimate
Bottom-upestimate
Top-down Cost Estimation First estimate the size.
– Count function points.– Estimate total lines of code (KLOC)
Apply Measured Productivity– Hours / Function Point or Hours / KLOC– Calibrate using local history or industry averages
Cost = size * productivity
Ease into measurement On a couple of projects, count the function points at the
beginning, and at every major release. At each point, take the effort expended and calculate
productivity (hours per function point delivered). Store for future use in estimating.
Other benefits of measurement Measurement can lead to improving:
– Cost performance– Methodology– Client Satisfaction– Credibility
The more weknow, the betterwe can do.
Functions
Goals
Quality
TasksPeople
Features
Plan
TimeScope
Any measurement should be: Simple Consistent Not technology or
platform dependent Not company dependent Useful at different points in
software lifecycle
The generic application
Application
Store and Update data
Push information in
Simple lookup
Produce report
Pull information in
Relative Difficulty Each function gets a number of “points” reflecting how
“hard” the function is to write. Each of these five functions can be complex, average, or
simple. To be consistent, there is a whole set of rules to decide
what function to use, and what level of complexity to measure it as.
Complexity Depending on requirements, some systems are harder to
write… that needs to be taken into account. Complexity factors are multiplied against the total of the
function points… causes the final number to range from 65% to 135%
Demo: Counting Tool Excel spreadsheet Pages for types of “files” (ILF, EIF) One page for all transaction types (EI, EO, EQ) Summary and Productivity pages Record of counter notes, constraints, use case notes, data
dictionary, any other pertinent information
Estimating Cost Start with a size measurement Multiply by productivity
– Dependent on platform, language, environment (IT shop vs. Outsource), project requirements (documentation, reviews, testing), etc.
Heavily dependent on historical performance
Demo: Productivity Calculations
Guidance on what industry or local averages are. Room for applying variances to averages + justifications Calculations by Rational Unified Process Workflow
Summary Measure size using simple
constructs, easy to understand Multiply size by productivity Requires measurement of past
projects to calibrate productivity As requirements improve, estimates improve
Software Estimation Resources International Function Point User’s Group
( www.ifpug.org ) – Certification – Counting Practices Manual
“Software Assessments, Benchmarks and Best Practices” by Capers Jones
“Software Cost Estimation with COCOMO2”by Barry Boehm, et. al.
Where to Get More InformationGlenn Briskin
Partner, Sierra Systems Group
360 570 4531
A. Nicklas Malik
Technical Architect
Certified Function Point Specialist
360 570 4546