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*DEPENDENCY DETERMINATION AND INTEGRATION
Dependencies may be characterized by the following attributes:
mandatory or discretionary, internal or external (as described below):
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*Mandatory dependencies.
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Mandatory dependencies are those that are legally or contractually required or inherent in the nature of the work.
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*Discretionary dependencies.
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Discretionary dependencies are sometimes referred to as preferred logic, preferential logic, or soft logic.
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*External dependencies.
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External dependencies involve a relationship between project activities and non-project activities.
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*Internal dependencies.
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Internal dependencies involve a precedence relationship between project activities and are generally inside the project team's control.
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*LEADS AND LAGS
A lead is the amount of time 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 2 weeks prior to the scheduled punch list completion.
This would be shown as a finish-to-start with a 2-week lead as shown in Figure 6.10. Lead is often represented as a negative value for lag in scheduling software.
A lag is the amount of time a successor activity will be delayed with respect to a predecessor activity.
For example, a technical writing team may begin editing the draft of a large document 15 days after they begin writing it.
This can be shown as a start-to-start relationship with a 15-day lag as shown in Figure 6.10.
Lag can also be represented in project schedule network diagrams as shown in Figure 6.11
in the relationship between activities H and I (as indicated by the nomenclature SS+10
(start-to-start plus 10 days lag) even though the offset is not shown relative to a timescale).