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Scheduling Work. I love deadlines. I love the sound they make as they fly by. -- Douglas Adams. What is the purpose of a project schedule?. Coordinate What to do and When? Monitor Are we on time? Are problems starting to occur? . Reminder : Why is software late?.

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scheduling work

Scheduling Work

I love deadlines.

I love the sound they make as they fly by.

-- Douglas Adams

what is the purpose of a project schedule
What is the purpose of a project schedule?
  • Coordinate
    • What to do and When?
  • Monitor
    • Are we on time?
    • Are problems starting to occur?
reminder why is software late
Reminder: 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 Practitioner’s Approach by Pressman

how to build a schedule which you already learned in csci 475 476
How to build a schedule(which you already learned in CSCI 475/476)
  • Determine dependencies of activities.
    • Major Activities are listed in the WBS.
    • Leverage past projects to determine dependencies.
    • Surprises are very bad.
  • Use dependencies to build activity network diagram (e.g. PERT chart).
  • Determine critical path.
  • Map network to a timeline (e.g. Gantt chart) using the effort estimates.
  • Use a software tool to help do this work.
dependency types
Dependency Types
  • External Dependency
    • Other projects
    • Stakeholders
    • Sub-Contractors
  • Internal Dependency
    • Audits (design, testing, documentation, …)
    • Sign-Offs at end of phase
dependency types1
Dependency Types

StartFinish

  • 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 testing is done
dependency types2
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.
activity networks
Activity Networks
  • CPM – Critical Path Method
    • activities are graph nodes (circles or squares)
    • single estimate for duration of tasks
  • PERT – Program Evaluation and Review Technique
    • activities are graph arcs (lines)
    • activity times are ranges and include probabilities
slide9

CPM Example

http://www.cs.unc.edu/~stotts/COMP145/homes/map/images/pert.gif

slide10

PERT Example

http://www.mckinnonsc.vic.edu.au/la/it/ipmnotes/ganttpert/pert_chart.gif

example activity network activity on node
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?

es=2ndwk ls=4thwk ef=3rdwk lf=5thwk

advanced scheduling topics
Advanced Scheduling Topics
  • Using Milestones
  • Managing Uncertainty in the Timeline
  • PERT confusion
  • Resource Leveling
  • Using Scheduling Tools
milestones
Milestones
  • Why must you schedule milestones, such as reviews, throughout the project?
managing uncertainty
Managing Uncertainty
  • Q: How confident can we be in our milestone dates and the delivery date?
  • Q: Can we calculate the confidence level?
  • A: Using confidence values 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 uncertainty1
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 problem
Common PERT Problem
  • K – integration testing
  • L – Install Software
  • M – Write Manual
  • N – Train Users

L

K

M

N

1

2

3

4

5

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…

pert problem cont
Pert Problem cont…
  • K – integration testing
  • L – Install Software
  • M – Write Manual
  • N – Train Users

L

3

K

1

2

M

N

4

5

But wait, the system needs to be installed before we can use it to train people. So…

pert problem cont1
Pert Problem cont…
  • K – integration testing
  • L – Install Software
  • M – Write Manual
  • N – Train Users

L

3

K

1

2

5

M

N

4

But what is that activity between dates 3 and 4? So…

pert problem cont2
Pert Problem cont…
  • K – integration testing
  • L – Install Software
  • M – Write Manual
  • N – Train Users

L

3

K

1

2

5

M

N

4

Dashed line is a dummy activity.

pert problem cont3
Pert Problem cont…
  • 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.

resource leveling
Resource Leveling
  • Leveling usually yields longer projects
  • Activity Shifting
    • to avoid using resources during a peak time.
    • use slack in start and end dates
  • Activity Splitting
    • to shorten duration
    • break long activity into pieces when more resources are available
  • Optimize the System, not individual tasks
leveling example
Leveling Example
  • What is the completion time?
  • Since F is so long, what would be the completion time if we break F into two parallel parts of 2wks and 3wks?

B

2wk

C

2wks

D

2wks

H

3wks

I

2wks

A

3wks

E

2wks

F

5wks

G

3wks

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