Estimation I: Delphi and Function Points

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Estimation IDelphi andFunction Points

• CSSE 372 - Software Project Management
• Don Bagert, Rose-Hulman Institute of Technology
• December 8, 2005
• Thanks to Mark Ardis for most of the slides
  included.

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Outline

• Estimation Accuracy
• Delphi method of estimation
• Function Points
• Function Point Wizard Demo

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Accuracy of Estimates Over Time
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Suggested Variances
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One Schedule Rule of Thumb

• Schedule months
• 3.0 (person-months 1/3)
• Schedule months How long the project will last
  in actual months

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Delphi Method of Estimation

• Encourage experts to converge on one estimate
• Works by encouraging outliers to change their
  estimates

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Basic Delphi Method

• Ask a group of experts to estimate a quantity.
• Distribute their estimates to one another.
• Ask for estimates again.
• Distribute estimates again.
• Repeat until this converges.

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Do Delphi Exercises 1 through 6
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Wideband Delphi

• Ask a group of experts to estimate a quantity.
• Distribute their estimates to one another, and
  allow them to discuss their reasoning.
• Ask for estimates again.
• Distribute with discussion again.
• Repeat until this converges.

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Do Delphi Exercises 7 though 12
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Discussion of Delphi Exercise

• What were your results?
• Why?

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Function Points
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Function Points in Pictures
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Function Point Variables

• External Inputs (EI)
• External Outputs (EO)
• External Inquiries (EQ)
• Internal Logical Files (ILF)
• External Interface Files (EIF)
• each is multiplied by a complexity factor

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How to Count Inputs

• Logical collection of data moved into application
  by a transaction
• Examples
• Input screen
• Interactive input
• Hardware input
• Batch input

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How to Count Outputs

• Logical collection of data moved out of an
  application by a transaction
• Examples
• Screen report
• Printed report
• Media outputs

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How to Count Inquiries

• Unique request/response that retrieves data from
  the application
• Examples
• Database query
• Menus
• Context-sensitive help

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How to Count Logical Files

• User-identifiable group of logically related data
  or control information maintained by the
  application
• Examples
• Data tables
• Database files

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How to Count External Interfaces

• User-identifiable group of logically related data
  or control information maintained by another
  application
• Examples
• Databases
• Fixed messages
• Shared files

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Unadjusted Function Points

• Sum of function point variables with complexity
  multipliers
• Assumes that no Value Adjustment Factors (VAFs)
  are needed

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Complexity Multipliers
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Backfiring

• What if you have a legacy system?
• Count lines of code
• Use correlation between lines of code and
  function points to estimate function points

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Value Adjustment Factors (VAFs)

• Data communication
• Distributed data processing
• Performance
• Heavily used configuration
• Transaction rate
• On-line data entry
• End-user efficiency

• On-line update
• Complex processing
• Reusability
• Installation ease
• Operational ease
• Multiple sites
• Facilitate change
• each multiplied by degree of influence(0-5)

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Data Communication

• 0 Batch
• 1 Remote printing or data entry
• 2 Remote printing and data entry
• 3 Teleprocessing front end
• 4 Significant teleprocessing
• 5 Dominantly teleprocessing

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Distributed Processing

• 0 Monolithic (single processor)
• 1 Prepare data for other components
• 2 A few components
• 3 More components
• 4 Many components
• 5 Dynamically performed on many components

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Adjusted Function Points

• Unadjusted FP (? VAFs / 100 0.65)
• Example
• 300 (25 / 100 0.65)
• 300 (0.25 0.65)
• 300 (0.90) 270

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Caper Jones's Estimate of Schedule Months
Raise function-point total to power in table
below
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FP ? Lines of Code

• Average correlation between function points and
  lines of code

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Function Point Wizard - Demo