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More on Scheduling
Recap of Last ClassRecap 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.
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
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
Common PERT Problems
Missing dependencies
Misinterpretation
Example
K – integration testing L – Install Software M – Write Manual N – Train Users
3 4 521K L M N
Example
K – integration testing L – Install Software M – Write Manual N – Train Users
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…
3 4 521K L M N
Example
K – integration testing L – Install Software M – Write Manual N – Train Users
But wait, the system needs to be installed before we can use it to train people. So…
3
4 5
21K
L
M N
Example
K – integration testing L – Install Software M – Write Manual N – Train Users
But what is that activity between dates 3 and 4? So…
3
4521
KL
M N
Example
K – integration testing L – Install Software M – Write Manual N – Train Users
Dashed line is a dummy activity.
3
4521
KL
M N
Example
Note: dummies not needed with "activity on node" graphs.
K N M
L
K – integration testing L – Install Software M – Write Manual N – Train Users
Resource LevelingResource 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
Example
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?
A3wks
B2wk
E2wks
C2wks
F5wks
G3wks
H3wks
I2wks
D2wks
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.
1. Identify: In order to manage a constraint, it is first necessary to identify it.
2. Exploit: Focus on how to get more production within the existing capacity limitations.
3. Subordinate: Prevent the materials needed next from waiting in a queue at a non-constraint resource.
4. Elevate: If, after fully exploiting this process, it still cannot produce enough products to meet market demand, find other ways to increase capacity.
5. Go back to Step 1.
Scheduling Tools
Gantt Chart producers MS Project
Web access Supports multiple projects Dependencies Billing support Resources leveling Gantt charts, activity network, …
MS Project
Open WorkBench
ATC Professional
