Project Scheduling

1
Project Scheduling

• Critical Path Method
• Based on material from Chapter 6 of Project
  Management and Teamwork, by Karl Smith

2
How do you schedule complex projects?

• Make a list of things to do?
• Use an outline?
• Draw a concept map?
• Focus on those things we know how to do first?
• Use project management software?

3
Dinner ConcertHow much time do you need to
prepare and consume the meal?

• Menu consists of soup and baked chicken
• Soup must be boiled 35 minutes and will allow 15
  minutes to serve and consume
• Chicken dish requires 30 minutes to boil rice, 15
  minutes to brown chicken in frying pan, 15
  minutes to bake rice and chicken in baking dish
• Sauce takes 5 minutes to prepare in frying pan
  and 15 minutes to boil peas
• Only have two pots and one frying pan
• Wine takes 5 minutes to uncork and 30 minutes to
  let breath before serving
• Allow 25 minutes to serve and consume entrée and
  wine

4
Meal Planning ExerciseWork Breakdown Structure
Boil Soup (Pot 1)
Eat Soup (Pot 1)
Eat Entree
Boil Peas (Pot 2)
Boil Rice (Pot 2)
Bake Entree
Brown Chicken (Fry Pan)
Prepare Sauce (Fry Pan)
Activity Name (Resource)
Open Wine
Wine Breathes
5
Critical Path Method

• Work breakdown structure ok for simple task with
  few activities
• When number of task large, a systematic solution
  is to use the Critical Path Method (CPM)
• to use CPM must know the duration of each
  activity and the predecessors of each

6
CPM - Forward Pass
Early Start (ES) - Earliest time that each
activity can start - obtained by adding the
earliest start of its latest starting predecessor
to the that predecessors duration - when two or
more activities must be competed before the next
one can start, then the maximum must be
used Early Finish (EF) - Determined by summing
the early start (ES) and duration
7
Meal Planning ExerciseCritical Path Method -
Forward Pass
35
50
0
35
Boil Soup 35
Eat Soup 15
50
75
Eat Entree 25
30
45
Boil Peas 15
0
30
30
45
Boil Rice 30
Bake Entree 15
0
15
15
20
Brown Chicken 15
Prepare Sauce 5
0
5
5
35
ES
EF
Open Wine 5
Wine Breathes 30
Activity Name duration
8
CPM - Backward Pass
Late Start (LS) - Latest possible starting time
that each activity can have - calculated as the
earliest starting successor, less the duration of
the activity under consideration Late Finish (LF)
- The resulting finish time based on late start
(LS)
9
Meal Planning ExerciseCritical Path Method -
Backward Pass
35
50
0
35
Boil Soup 35
Eat Soup 15
50
35
50
75
35
0
Eat Entree 25
30
45
75
50
Boil Peas 15
0
30
30
45
50
35
Boil Rice 30
Bake Entree 15
35
5
50
35
0
15
15
20
Brown Chicken 15
Prepare Sauce 5
30
15
35
30
0
5
5
35
ES
EF
Open Wine 5
Wine Breathes 30
Activity Name duration
20
15
50
20
LF
LS
10
CPM - Critical Path Floats
Critical Path - The path for which activities
cannot be delayed - activities on critical path
will have equal earliest and latest times and are
call critical Floats - The amount the termination
of an activity can be delayed before delaying a
successor is called free float (FF). FFi
(ESi1) min - ESi - Di The amount of slack an
activity has before it would cause the path on
which it lies to become critical is called the
total float (TF). TFi LFi - EFi
11
Meal Planning Exercise
Critical Path
35
50
0
35
Boil Soup 35
Eat Soup 15
50
35
50
75
35
0
Eat Entree 25
30
45
75
50
Boil Peas 15
0
30
30
45
50
35
Boil Rice 30
Bake Entree 15
35
15
50
35
0
15
15
20
Brown Chicken 15
Prepare Sauce 5
FF 50 - 30 - 15 5
30
15
35
30
0
5
5
35
ES
EF
Open Wine 5
Wine Breathes 30
Activity Name duration
20
15
50
20
LF
LS
12
CritPath Programhttp//www.ce.umn.edu/smith

• Allows easy entry of activites
• Provides critical path calculations (ES, EF, LS,
  LF, Float) and algorithm stepper
• Calculates critical path
• Gives associated Gantt Chart - a time-scaled
  network (Gantt Chart does not show
  interdependence)