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17spm_L10

Scheduling, Planning and Tracking

SPM 2017 © Ron Poet Lecture 10 1

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.

SPM 2017 © Ron Poet Lecture 10 2

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 1950’s

o Also called critical path and network analysis.

� Gantt = technique invented by Henry Gantt.

SPM 2017 © Ron Poet Lecture 10 3

o American Mechanical Engineer and Management Consultant.

o Developed in 1910’s.

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.

SPM 2017 © Ron Poet Lecture 10 4

� 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.

SPM 2017 © Ron Poet Lecture 10 5

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.

SPM 2017 © Ron Poet Lecture 10 6

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.

SPM 2017 © Ron Poet Lecture 10 7

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.

SPM 2017 © Ron Poet Lecture 10 8

� 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

SPM 2017 © Ron Poet Lecture 10 9

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.

SPM 2017 © Ron Poet Lecture 10 10

� 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

SPM 2017 © Ron Poet Lecture 10 11

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

SPM 2017 © Ron Poet Lecture 10 12

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

SPM 2017 © Ron Poet Lecture 10 13

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)

SPM 2017 © Ron Poet Lecture 10 14

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

SPM 2017 © Ron Poet Lecture 10 15

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)

C 5 5 5 (from D) 0

D 1 C 6 6 (from E,
G)

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

Recording Information

� A node for an activity contains:

� Description:

� Duration:

� Earliest Start:

� 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.

� 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.

� Activities not on the critical path can be shifted and lengthened, using
up the slack.

o They can’t 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.

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.

� 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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