Project Management Processes in Organizations
(PM600-1804B-01)
Scheduling Techniques for
Planning and Executing
Introduction
This lesson examines essential scheduling tools and techniques for planning
and executing the work of a project. This lesson explains the four
predecessor–successor relationships, along with lead time and lag time, used
to model the sequence of activities. Network diagrams are used to
graphically represent the sequence of activities. The critical path method is
applied to the network diagram after durations have been estimated to
discover the critical path in the sequence of activities. The critical chain
method is applied to the critical path network diagram to introduce schedule
buffers to account for uncertainties. The schedule compression techniques of
fast-tracking and crashing the schedule are used for optimizing the schedule
during planning and for keeping the work on schedule during execution.
Learning Materials
Predecessor–Successor Relationships
Every activity in a project schedule must have an activity that proceeds it,
except for the first activity, the start of the project, and every activity in a
project schedule must have a successor activity that follows it, except for the
last activity at the end of the project. Predecessor–successor
relationships are used to model the following four types of dependencies:
Mandatory dependencies are naturally inherent in the work.
For example, before framing a house, the subfloor must be
constructed; thus, the predecessor activity is construct the
subfloor, and the successor is framing.
Discretionary dependenciesrefer to preferred sequences of (Lewis,
activities that have alternative sequences. The preferences 2017)
may be because of accepted best practices of an
application area.
, External dependencies refer to activities or events that are not a part
of the project that affect activities that are part of the project. For
example, needing Environmental Protection Agency approval before
building a section of railroad track could occur.
Internal dependencies refer to the predecessor relationships of
activities within the project.
To fully understand how predecessor relationships work, project managers
must extend their definition of predecessor in the context of scheduling to
mean the driving activity, as demonstrated below. The predecessor–
successor relationships of the four types of dependencies are modeled by
using the following four logical relationships in conjunction with any lead
times or lag times:
Finish-to-Start (FS): “A successor activity cannot start until a
predecessor activity has finished” (Project Management Institute,
2013), as depicted in the first diagram of Figure 1, where Task A is the
predecessor and Task B is the successor. However, in the second
diagram when the lead time is applied, the definition does not hold.
The lead time is indicated by the double red arrow in the second
diagram and represents the amount of lead the start of the successor
has before the finish of the predecessor. Thus, one’s meaning of the
word “predecessor” must be extended to mean the driving activity
because if the finish of Task A is delayed, it drives a late start for Task
B. Likewise, an early Task A finish drives an early Task B start, as shown
in diagrams 3 and 4, respectively, in Figure 1.
Lag time, the interval of time after Task A finishes that Task B would start,
works similarly. This principle of the “driving activity” will now be applied to
the remaining three predecessor relationships.
Finish-to-Finish (FF): “A successor activity cannot finish until a
predecessor activity has finished” (Project Management Institute,
2013). Here again, when lead time is applied to the finish of the
successor, the definition does not hold because clearly the successor
activity can finish before the predecessor activity finishes. More
accurately stated, in the FF relationship, the finish of the predecessor
drives the finish of the successor. See Figure 2
Start-to-Start (SS): “A successor activity cannot start until a
predecessor activity has started” (Project Management Institute,
2013). Here again, when lead time is applied to the start of the
(PM600-1804B-01)
Scheduling Techniques for
Planning and Executing
Introduction
This lesson examines essential scheduling tools and techniques for planning
and executing the work of a project. This lesson explains the four
predecessor–successor relationships, along with lead time and lag time, used
to model the sequence of activities. Network diagrams are used to
graphically represent the sequence of activities. The critical path method is
applied to the network diagram after durations have been estimated to
discover the critical path in the sequence of activities. The critical chain
method is applied to the critical path network diagram to introduce schedule
buffers to account for uncertainties. The schedule compression techniques of
fast-tracking and crashing the schedule are used for optimizing the schedule
during planning and for keeping the work on schedule during execution.
Learning Materials
Predecessor–Successor Relationships
Every activity in a project schedule must have an activity that proceeds it,
except for the first activity, the start of the project, and every activity in a
project schedule must have a successor activity that follows it, except for the
last activity at the end of the project. Predecessor–successor
relationships are used to model the following four types of dependencies:
Mandatory dependencies are naturally inherent in the work.
For example, before framing a house, the subfloor must be
constructed; thus, the predecessor activity is construct the
subfloor, and the successor is framing.
Discretionary dependenciesrefer to preferred sequences of (Lewis,
activities that have alternative sequences. The preferences 2017)
may be because of accepted best practices of an
application area.
, External dependencies refer to activities or events that are not a part
of the project that affect activities that are part of the project. For
example, needing Environmental Protection Agency approval before
building a section of railroad track could occur.
Internal dependencies refer to the predecessor relationships of
activities within the project.
To fully understand how predecessor relationships work, project managers
must extend their definition of predecessor in the context of scheduling to
mean the driving activity, as demonstrated below. The predecessor–
successor relationships of the four types of dependencies are modeled by
using the following four logical relationships in conjunction with any lead
times or lag times:
Finish-to-Start (FS): “A successor activity cannot start until a
predecessor activity has finished” (Project Management Institute,
2013), as depicted in the first diagram of Figure 1, where Task A is the
predecessor and Task B is the successor. However, in the second
diagram when the lead time is applied, the definition does not hold.
The lead time is indicated by the double red arrow in the second
diagram and represents the amount of lead the start of the successor
has before the finish of the predecessor. Thus, one’s meaning of the
word “predecessor” must be extended to mean the driving activity
because if the finish of Task A is delayed, it drives a late start for Task
B. Likewise, an early Task A finish drives an early Task B start, as shown
in diagrams 3 and 4, respectively, in Figure 1.
Lag time, the interval of time after Task A finishes that Task B would start,
works similarly. This principle of the “driving activity” will now be applied to
the remaining three predecessor relationships.
Finish-to-Finish (FF): “A successor activity cannot finish until a
predecessor activity has finished” (Project Management Institute,
2013). Here again, when lead time is applied to the finish of the
successor, the definition does not hold because clearly the successor
activity can finish before the predecessor activity finishes. More
accurately stated, in the FF relationship, the finish of the predecessor
drives the finish of the successor. See Figure 2
Start-to-Start (SS): “A successor activity cannot start until a
predecessor activity has started” (Project Management Institute,
2013). Here again, when lead time is applied to the start of the
