Scheduling Work

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Scheduling Work

• I love deadlines.
• I love the sound they make as they fly by.
• -- Douglas Adams

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Why is software late?

• Under-Estimate of effort.
• Unrealistic deadlines imposed by outsiders.
• Changing requirements.
• Risks that were not considered.
• Technical problems that could not be foreseen.
• Failure to recognized that the project is falling
  behind schedule and lack of action to correct the
  problem.
• Software Engineering A Practitioners Approach
  by Pressman

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How to build a schedule

• Determine dependencies of activities found in
  WBS.
• Use dependencies to build activity network
  diagram (eg PERT).
• Determine critical path.
• Map network to a timeline (eg Gantt Chart) using
  the effort estimates.
• Use a software tool to help do this work.

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Why Determine Dependencies?

• Dependencies determine deadlines and when work
  can begin.
• The WBS shows hierarchy, not dependency.
• Planners must find all dependencies.
• Surprises are very bad!

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Dependency Types

• External Dependency
• Other projects
• Stakeholders
• Sub-Contractors
• Internal Dependency
• Audits (design, testing, documentation, )
• Sign-Offs at end of phase

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Dependency Types

• Start Finish
• FS - T2 cannot start until T1 is finished.
• coding must wait on design to be finished
• SS - T1 and T2 must start at same time.
• documentation and coding start together
• FF - T1 and T2 finish at same time.
• configuration management ends when coding is done

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Dependency Types

• Lag T2 cannot start until a given amount of
  time after T1 is done.
• Start on-site training one week after final demo
  to customer management group.
• Soft T2 should start after T1, but it is not
  completely essential that T1 be finished.
• Populate the new database after the database has
  been built. If the new database is not
  completely finished we can still populate the few
  finished tables.

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Activity Networks

• CPM Critical Path Method
• activities are graph nodes (circles)
• single estimate for duration of tasks
• PERT Program Evaluation and Review Technique
• activities are graph arcs (lines)
• activity times are ranges and include
  probabilities

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http//www.cs.unc.edu/stotts/COMP145/homes/map/im
ages/pert.gif
10
http//www.mckinnonsc.vic.edu.au/la/it/ipmnotes/ga
nttpert/pert_chart.gif
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Example Activity Network Activity on Node
1wks
2wks
T5
T2
1wk
3wks
1wk
2wks
1wk
T1
T4
T6
T8
T9
4wks
T3
3wks
T7

• Questions
• Minimum time to complete the project?
• Critical Path?
• Earliest start time, latest start, earliest
  finish, latest finish?
• For T2 ? es2ndwk ls4thwk ef3rdwk
  lf5thwk

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Resulting Gantt Chart
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Next Time

• Making Good PERT charts
• Resource Leveling
• Matching to the Calendar and External Resources
• Correcting Misinterpretations
• Managing Uncertainty
• Automated Tools