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6 - PROJECT TIME MANAGEMENT

• discretionary dependencies. Discretionary dependencies are sometimes referred to as preferred logic,
preferential logic, or soft logic. Discretionary dependencies are established based on knowledge of best
practices within a particular application area or some unusual aspect of the project where a specific
sequence is desired, even though there may be other acceptable sequences. Discretionary dependencies
should be fully documented since they can create arbitrary total float values and can limit later scheduling
options. When fast tracking techniques are employed, these discretionary dependencies should be
reviewed and considered for modification or removal. The project team determines which dependencies
are discretionary during the process of sequencing the activities.
• External dependencies. External dependencies involve a relationship between project activities and
non-project activities. These dependencies are usually outside the project team’s control. For example,
the testing activity in a software project may be dependent on the delivery of hardware from an external
source, or governmental environmental hearings may need to be held before site preparation can begin
on a construction project. The project management team determines which dependencies are external
during the process of sequencing the activities.
• Internal dependencies. Internal dependencies involve a precedence relationship between project
activities and are generally inside the project team’s control. For example, if the team cannot test a
machine until they assemble it, this is an internal mandatory dependency. The project management team
determines which dependencies are internal during the process of sequencing the activities.

6.3.2.3 Leads and Lags

A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor
activity. For example, on a project to construct a new office building, the landscaping could be scheduled to start
two weeks prior to the scheduled punch list completion. This would be shown as a finish-to-start with a two-week
lead as shown in Figure 6-10. Lead is often represented as a negative value for lag in scheduling software.

Complete Write
Punch List Draft

FS – 2 Weeks (Lead) SS – 15 Days (Lag)

Landscape Edit
Building Lot Draft

Figure 6-10. Examples of Lead and Lag

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