Software Development Estimation Dark Art or Science? Stefan Kiryazov (Vereo, Wizefish)

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Introduction Target audience Required background skills Senior software developers Technical leaders Project managers High level managers Customers Required background skills Familiarity with the software development process

Causes for Uncertainty Presenting Estimates Estimation Process Contents Causes for Uncertainty Presenting Estimates Estimation Process Corporate Portals, Enterprise Portals, Enterprise Portal Servers

Background Why is estimating important? A foundation for efficient development Estimate too high – Parkinson’s law Estimate too low – inefficient planning Is perfect estimating possible? The software estimating story

Cost Budgeting

Causes for Uncertainty Will the customer want Feature X? Will the customer want the cheap or expensive version of Feature X? If we go for the cheap, will he/she want the expensive one later after all? How will Feature X be designed? How long will it take to fix the bugs in Feature X? How long will it take to integrate Feature X?

Causes for Uncertainty Software development – a process of gradual refinement The perfect estimate is doing the project work itself The earlier, the less precise

Estimate Convergence Graph

“It is the mark of an instructed mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness when only an approximation of the truth is possible …” Nichomachean Ethics, Aristotle

The Schedule Graph

Optimistic Schedule Graph

Avoid overprecise estimates Presenting Estimates Presentation styles Plus/minus Conditions Cases Ranges Avoid overprecise estimates Accuracy vs precision Use coarse periods

Estimation Process Size estimation Effort estimation Schedule estimation

Compare with past projects Size Estimation What is size? Function points Lines of code Custom measurement Compare with past projects Compare with documented data, not personal memory

Derived from size estimate No off-the-cuff estimates! Effort Estimation Derived from size estimate No off-the-cuff estimates! Even with conditions! Estimate at high level of detail Law of large numbers

Don’t omit common tasks Developer based estimates Effort Estimation Don’t omit common tasks Developer based estimates Sanity checking Commitment-based estimates Compare estimates

The Cost Graph

Compression increases cost! Schedule Estimation The nominal schedule Schedule = 3 * Effort1/3 Schcedule – months, Effort - manmonths Schedule compression Compression Factor (CF) = Nominal / Compressed Compression increases cost! Compressed cost = Initial cost / CF

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