Scheduling%20Work

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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
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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?
• For T2, what are the earliest start time, latest
  start, earliest finish, latest finish?
• es2ndwk ls4thwk ef3rdwk lf5thwk

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Resulting Gantt Chart
1 2 3 4 5 6 7 8 9 10 11 12 13 14
T1
T2
T3
T4
T5
T6
T7
T8
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Managing Uncertainty

• Q How confident can we be in our milestone dates
  and the delivery date?
• A Using confidence and Statistics
• for each task, determine pessimistic and
  optimistic times
• if PT-OT is small for all tasks, then great!!!
• compute average PT-OT, and std dev
• if a task's PT-OT is outside the std dev, worry
  about that task

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Managing Uncertainty

• Q Where do we schedule uncertainty time?
• A1 spread it out by bumping each milestone.
• used by Critical Path
• A2 lump it together as one activity at end.
• used by Critical Chain

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Common PERT Problems

• Missing dependencies
• Misinterpretation

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Example

• K integration testing
• L Install Software
• M Write Manual
• N Train Users

L
K
M
N
3
4
5
2
1
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Example

• K integration testing
• L Install Software
• M Write Manual
• N Train Users

L
K
M
N
3
4
5
2
1
But wait, we can shorten the project if we write
the manual right after testing is finished. (L
and M can be done in parallel.) So
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Example

• K integration testing
• L Install Software
• M Write Manual
• N Train Users

L
3
K
2
1
M
N
4
5
But wait, the system needs to be installed
before we can use it to train people. So
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Example

• K integration testing
• L Install Software
• M Write Manual
• N Train Users

L
3
K
2
1
5
M
N
4
But what is that activity between dates 3 and 4?
So
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Example

• K integration testing
• L Install Software
• M Write Manual
• N Train Users

L
3
K
2
1
5
M
N
4
Dashed line is a dummy activity.
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Example

• K integration testing
• L Install Software
• M Write Manual
• N Train Users

L
K
N
M
Note dummies not needed with "activity on node"
graphs.
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Resource Leveling

• Activity Shifting
• to avoid using resources during a peak time.
• use slack in start and end dates
• Activity Splitting
• to shorten duration
• break activity into pieces when more resources
  are available
• Optimize the System, not individual tasks
• Leveling usually yields longer projects

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Example
B 2wk
C 2wks
D 2wks
H 3wks
I 2wks
A 3wks
E 2wks
F 5wks
G 3wks

• What is the completion time?
• Since F is so long, what would be the completion
  time if we break it into two parallel parts of
  2wks and 3wks?

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Theory of Constraints

• The Goal by Goldratt in 1997
• Traditional approach is to divide and divide into
  manageable parts, then optimize these parts.
• TOC looks at the whole system.
• Identify In order to manage a constraint, it is
  first necessary to identify it.
• Exploit Focus on how to get more production
  within the existing capacity limitations.
• Subordinate Prevent the materials needed next
  from waiting in a queue at a non-constraint
  resource.
• Elevate If, after fully exploiting this process,
  it still cannot produce enough products to meet
  market demand, find other ways to increase
  capacity.
• Go back to Step 1.

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Scheduling Tools

• Gantt Chart producers
• MS Project
• Web access
• Supports multiple projects
• Dependencies
• Billing support
• Resources leveling
• Gantt charts, activity network,

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MS Project
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Open WorkBench
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ATC Professional
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And finally