Scheduling WorkScheduling Work

I love deadlines.

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

What is the purpose of a project schedule?

1. Coordinate What to do and When?

2. Monitor Are we on time? Are problems starting to occur?

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)

1. Determine dependencies of activities. Major Activities are listed in the WBS. Leverage past projects to determine dependencies. Surprises are very bad.

2. Use dependencies to build activity network diagram (e.g. PERT chart).

3. Determine critical path.

4. Map network to a timeline (e.g. Gantt chart) using the effort estimates.

Use a software tool to help do this work.

Dependency Types

External Dependency Other projects Stakeholders Sub-Contractors

Internal Dependency Audits (design, testing, documentation, …) Sign-Offs at end of phase

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 testing

is done

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

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

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

CPM ExampleCPM Example

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

PERT ExamplePERT Example

Example Activity Network – Activity on Node

T1

T2

T3

T4 T6

T5

T7

T8 T9

1wk

2wks

4wks

3wks

1wks

1wk

3wks

2wks 1wk

Questions:1. Minimum time to complete the project?2. Critical Path?3. For T2, what are the earliest start time, latest start, earliest finish, latest finish?

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

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

Advanced Scheduling TopicsAdvanced Scheduling Topics

Using Milestones

Managing Uncertainty in the Timeline

PERT confusion

Resource Leveling

Using Scheduling Tools

Milestones

Why must you schedule milestones, such as reviews, throughout the project?

Managing Uncertainty

Q:Q: How confident can we be in our milestone dates and the delivery date?

Q:Q: Can we calculate the confidence level?

A:A: Using confidence values and Statistics1. for each task, determine pessimistic and optimistic times

2. if PT-OT is small for all tasks, then great!!!

3. compute average PT-OT, and std dev

4. 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 Problem

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

Pert Problem cont…

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

Pert Problem cont…

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

Pert Problem cont…

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

Dashed line is a dummy activity.

3

4521

KL

M N

Pert Problem cont…

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

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

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?

A3wks

B2wk

E2wks

C2wks

F5wks

G3wks

H3wks

I2wks

D2wks

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

And finally…And finally…