17spm_L10
Scheduling, Planning and Tracking
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PERT, Gantt and Earned Value Charts
Scheduling and Tracking
Scheduling decides when to start a particular activity.
Tracking is monitoring where you are and whether you are on
schedule.
Several formal techniques can be used.
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o A PERT chart shows the sequence in which activities take place.
o A Gantt chart shows the start and end date of each activity.
o An Earned Value chart is a graph of elapsed time verses effort.
PERT and Gantt Charts
PERT = Program Evaluation and Review Technique.
o Developed by USA Navy in 1950s
o Also called critical path and network analysis.
Gantt = technique invented by Henry Gantt.
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o American Mechanical Engineer and Management Consultant.
o Developed in 1910s.
o Used for the Hoover Dam and Interstate Highway projects.
PERT Chart
Shows the sequence of tasks and how they relate to other tasks.
Each task may have some earlier tasks that it depends on and other
tasks that depend on it.
Each task also has an elapsed time that it will take.
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The chart is a graph of nodes connected by lines.
The critical path is the shorted time that the project will take.
o All the nodes on the critical path must be done one after the other
with no time gaps between them.
Activities and Milestones
An activity takes a certain amount of time.
A milestone is the endpoint of an important activity and leads to the
start of the next activity.
o Must have a measurable outcome that is either true or false and can
be ticked off.
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be ticked off.
A deliverable is delivered to a customer who may be an internal
customer.
o Are usually milestones.
o Can be documents such as requirements spec.
o Can be software component or working system.
Resources
People are the most important resource.
o Must be enough people with specialist skills.
Too few specialist can make it difficult to:
o Carry out sufficient activities in parallel.
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o
o Cause a bottleneck for certain aspects such as testing.
Training in the early part of a project may be an important activity.
o Deliverable is trained members of the team.
Project Planning
Divide into separate activities.
o Define the activity.
o Identify milestone that will show that it has ended.
o Estimate the effort required.
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o
o Estimate the minimum elapsed time required.
Determine the dependencies between activities.
o Which activities must be finished before the next can start.
Find the critical path(s).
o Activities that must stick to their schedules.
Find activities that have some slack time.
o Not on the critical path.
PERT
Used to find the critical path(s).
Find the minimum time for the whole project based on:
o Minimum times for each activities.
o Dependencies between activities.
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o
Critical activities and those with some slack are revealed.
Two forms of PERT chart.Both record the same information.
o Activity as a Node.I will use this style.
o Activity as an Arc
The effort required for each activity is not needed to determine the
critical path.Just the elapsed time is important.
It is useful for resource planning.
Example: PERT Chart Initial Information
Task Elapsed Dependencies
A 4
B 3
C 5
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D 1 C
E 4 B, D
F 5 A, E
G 5 B, D
H 6 C
Forward Pass
Find the earliest time Ei that each activity can finish.
Start from the beginning and follow all routes through the graph.
The earliest time Ei for an activity to finish is the earliest time that the
previous activity could finish + the length of this activity.
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If there is more than one route to get to the activity, take the maximum
value of the various Ei values.
Record this in the activity.
Example: PERT Chart Forward Pass
Task Elapsed Dependencies Earliest Finish
A 4 4
B 3 3
C 5 5
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D 1 C 6
E 4 B, D 10 (max 7, 10)
F 5 A, E 15 (max 9, 15)
G 5 B, D 11 (max 8, 11)
H 6 C 11
Backward Pass
Find the latest time Li that an activity can finish.
Find the maximum finishing time for all activities.
Start from the end and follow the graph backwards towards the start.
The earliest finishing time for an activity is the earliest finishing time
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of the activity it leads to, minus the length of this activity.
If more than one path leads from an activity, choose the smallest of the
Li values.
Record this in the activity.
A dependency graph helps at this stage.
Dependency Graph
A F
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E
G
H
DC
B
Example: PERT Chart Backward Pass
Task Elapsed Dependencies Earliest Finish Latest Finish
A 4 4 10 (from F)
B 3 3 6 (from E, G)
C 5 5 5 (from D)
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D 1 C 6 6 (from E, G)
E 4 B, D 10 (max 7, 10) 10 (from F)
F 5 A, E 15 (max 9, 15) 15
G 5 B, D 11 (max 8, 11) 15
H 6 C 11 15
Slack Time
The slack time Si for each activity = Li Ei.
If the slack time Si = 0 then the activity is on the critical path.
The critical path(s) are all paths connecting the critical activities.
If any critical task is delayed then the project as a whole will be
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delayed.
Free Float = amount of time an activity can be delayed without
affecting any of the other activities.
Total float = amount of time an activity can be delayed without
delaying the project as a whole.
o Some other non critical activities may also be delayed.
Slack time can also be used to spread an activity out longer than its
minimum time.
Example: PERT Chart Backward Pass
Task Elapsed Dependenci
es
Earliest Finish Latest
Finish
Slack Time
A 4 4 10 (from F) 6
B 3 3 6 (from E,
G)
3
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G)
C 5 5 5 (from D) 0
D 1 C 6 6 (from E,
G)
0
E 4 B, D 10 (max 7, 10) 10 (from F) 0
F 5 A, E 15 (max 9, 15) 15 0
G 5 B, D 11 (max 8, 11) 15 4
H 6 C 11 15 4
Dependency Graph: Critical Path
A F
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E
G
H
DC
B
Recording Information
A node for an activity contains:
Description:
Duration:
Earliest Start:
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Latest Start:
Earliest Finish: from earliest start and duration
Latest Finish: from latest start and duration
Float:
Activity Span: actual duration, can be longer if non-critical.
PERT Chart for MSc SD
Prog, DTA, SN, SPM, ECS: stand alone.
AP, ADS depend on Prog.
TeamProj depends on Prog, DTA, SPM.
SE depends on SPM.
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2 options: stand alone.
Exams depend on all above.
Summer project depends on Prog and Exams.
Elapsed time: 3 months for each activity.
Effort: 10 hours per credit.
Gantt Chart
The x-axis is time.
Each different activity is listed on the y-axis
Activities are long rectangles, with the critical path in black.
Milestones appear as diamonds.
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Activities not on the critical path can be shifted and lengthened, using
up the slack.
o They cant be shortened.
We can record the effort and staff required for each activity.
o Get an idea of employment over time.
Gantt Chart: MSc SD | IT
Scheduling by semesters.
Milestones:
o End December with option to switch to IT.
o End of exams with option to take resits, extend the program.
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o
o End of resits with option to take Diploma.
Earned Value Chart
The x-axis is the elapsed time.
The y-axis is the effort expended.
The planned project work is one line on this graph.
The actual progress is plotted as another line on the graph.
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The difference between the two lines will show:
o Difference in effort expended
o Difference in elapsed time.
Used to estimate actual completion time and cost.
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