Estimation and scheduling

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Estimation and scheduling
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Estimating --

• An iterative process
• Done in the planning and budgeting stage
• After Conceptualization Definition, 50-100 off
• At the end of Planning Budgeting, 10-25 off
• A good WBS is absolutely essential to do
  estimating

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Estimating Techniques

• Professional Judgment
• History (database)
• Formulas

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When is Estimating Done??

• Outside of the four stages
• In Project Portfolio Design
• Lots of projects
• These projects must be estimated in terms of
  duration and cost
• These projects must be prioritized
• These projects must be sequenced

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Rough-cut Estimation

• WAGs Wild ________ Guesses
• SWAGs Scientific Wild ______ Guesses
• You want to err on the high side
• If you set your estimates as to duration and cost
  too high, your project may not be chosen

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Project Selection

• In the absence of dependency constraints,
  projects get prioritized in terms of benefit/cost
• Projects with the highest benefit/cost ratio will
  get performed first, assuming no dependencies
  between projects

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Use of Professional Judgment

• Based on WBS, an expert judgment estimate is made
  for each work package
• The person assigned to the work package also
  estimates the time required to complete it
• The person assigned to the work package will make
  every effort to complete the task in the time he
  estimated it would take
• Amazingly accurate when experts are available
• Often, however experts arent available

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Why do you think .

• Estimates based on Expert Judgment are so
  Accurate (according to one author)?

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Use of History Database

• For this to work, your firm must keep a history
  database
• The database should record how long each task
  took and who did the task
• Break new projects up into tasks that have a
  history database
• 8 to 1 productivity ratio between fastest and
  slowest professional

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Consider the Waterfall Model for Software
Development

• Definition Phase
• Analysis Phase
• Design Phase
• Construction (Coding) Phase
• Testing Phase
• Conversion/Cutover Phase
• Training Phase
• Operation Phase

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Consider Just the Testing Phase

• Module testing
• Integration testing
• System testing
• Beta testing
• Final acceptance test

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How much time should be devoted to testing??

• In any technology product context?

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Questions, Contd

• How much of the total time does Brooks devote to
  Definition, Analysis and Design?
• 1/3
• How much time to coding?
• 1/6 to Coding
• How much time to testing?
• 1/4 to component test and early system test
• 1/4 to total system test

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In other words,

• Half of the total time should be devoted to
  testing, especially if it is a brand new product

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Use of Formulas

• COCOMO--project cost, effort, schedule, staffing
  for each of the phases
• Preliminary design
• Detailed design
• Code and unit test
• System test
• COCOMO was developed by Barry Boehm in
  1981--COnstructive COst MOdel

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Inputs to COCOMO

• Monthly cost of staff involved
• Factors indicating the general level of
  complexity of the software
• Programming practices and tools used
• Experience of staff
• Lines of LOSC--rendering COCOMO unusable

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Function Points

• A user input
• User display
• Peripheral I/O
• Restructuring data
• Condition checking
• Calculation
• Branching

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Function point approach--BEFORE YOU LEAP

• Vendor is Gordon Group
• It must know how many Source Lines of Code (SLOC)
  are required for each function point.
• It calculates total SLOC based on function points
  it knows about and feeds this into the COCOMO
  algorithm

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Estimacs from CA (Computer Associates)

• Can take into account modern code generation
  tools
• Determines effort, but also
• Hardware required
• financial break-even analysis
• risk analysis
• maintenance costs
• Expensive gt 20K

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Estimating using Function Points

• D C ( G J)
• D is the task duration in person-days
• C is the complexity of the task
• G is the assigned persons general experience
• J is the assigned professionals job knowledge
  factor

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Complexity

• Must break task down into its smallest possible
  repeatable functions
• Then add up the complexity of each function
• User input, user display, peripheral I/O,
  restructuring data, condition checking,
  calculation, etc.
• Repeatable functions are called function points.
• Function points are graded as SIMPLE, COMPLEX and
  VERY COMPLEX

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Productivity

• Your average project player gets a productivity
  factor of 1 for G
• Slower players get factors gt 1
• Faster players get factors lt 1

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Formula method conclusions

• Will work if you develop accurate factors
• Can be used for any task from building a house to
  developing software
• Depends on how well you granularize

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This breaks down to

• PLAN -- 40
• BUILD -- 20
• TEST -- 40
• The point is . allocate lots of time to testing

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Another Rule of Thumb

• The time to design, document and code a module
• equals the time to debug it
• According to Gildersleeve

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Can you use RATIOS for Forecasting?

• Suppose you found that it took 20 days to do
  Planning.
• How long, based on ratios will it take to do the
  project?

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Conclusions to Estimating

• Our weakest talent
• Estimating is iterative
• Estimating is still an art

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Scheduling --

• Also assists with estimating, especially when PM
  software is used

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PM software supports

• WBS
• Gantt
• PERT
• Calendar(s)
• Resources and their assignments

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Networks

• Use activity on node approach
• doesnt require dummy activities
• Understand what float is--it is slack
• Critical path is the longest path
• shows precedent activities, relationships
• doesnt show what will be done when, by whom

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Resource allocation

• Assign tasks to individuals whose skill level
  suits the task
• Assign similar tasks to the same person
• Assign time-critical tasks to your most reliable
  people
• Assign tasks that communicate to the same
  individual to minimize peoples interaction
• Dont assign too many different tasks to any one
  individual

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Reducing task duration by adding manpower

• Add 20 direct time for each additional member on
  a professional team
• If it takes 10 person days for one person, it
  will take 12 person days for two people, 14.4
  person days for three people, etc.

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Cost effects of adding resources

• More resources, gets the project done sooner,
  USUALLY
• But it also costs more
• The PM must come up with the best balance,
  depending on the priorities set by management or
  the user

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Shortening the duration of projects

• Fast tracking
• Crashing
• Adding resources to the critical path
• Allowing your current CP teams members to work
  overtime

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Crashing projects

• Crash tasks on the critical path only, only as
  long as no other path becomes critical
• If other paths become critical, the analyst must
  crash those as well

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Gantt Chart

• a time bar chart
• Invented by Henry Gantt in 1910
• Determine the units of time
• Mark all known calendar events at bottom
• Schedule each activity from PERT

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Conclusions to Scheduling

• Use PM software--worth every penny
• Do at least one PERT and one GANTT manually, just
  to get a feel for the process