More on Scheduling

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More on Scheduling
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Recap of Last Class

• Activity dependencies are shown through
  CPM/PERT Chart.
• Critical path
• Completion date
• Slack time in non-critical path activities
• Activity start and end dates and personnel
  responsibilities shown on Gantt Chart.

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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