Dynamic Minimum Lag Relationship - Construction Project Scheduling and Control - page 341

For example, in building construction, this relationship can be used for the series of
four activities: framing, drywall, pasting and taping, and wall painting. In infrastructure
construction, it can be used for trench excavating, subbase, laying pipe, backfilling, and
compaction operations. The DML relationship can have numerous applications in all
types of projects.
The DML relationship eliminates the need for the SS + FF combination rela-
tionship and most of the situations in which a single SS or FF relationship is used. 4
However, there will be a few situations in which a single SS or FF relationship can still
be used (e.g., in the case of a developer who is planning to build an apartment com-
plex on a large piece of land). In this case, the developer needs to “Clear and Grub” a
certain portion of the land where the building will be erected. There is no connection
between the finish “Clear and Grub” and “Excavate,” as shown in Figure 12.7. The
scheduler, in this case, has to make sure that the minimum required percentage of
“Clear and Grub” is completed before the excavation can start. A safer way to depict
that logic is demonstrated in Figure 12.8.
An example of FF relationship dependency that does not require a DML relation-
ship is the situation in Figure 12.9. The Landscape activity's start is independent of
the Parking Lot activity, but you need to finish the Parking Lot activity before you can
finish the Landscape activity.
The DML relationship is a new concept. It may, and most likely will, need more
research and fine-tuning before it is applied commercially.

5

Clear & Grub
20

Excavate
8

Figure 12.7 A situation in which the DML relationship cannot be used in lieu of the SS
relationship

Clear & Grub I
5

Excavate
8

Clear & Grub II
15

Figure 12.8 A better alternative to depict the logic of the network in Figure 12.7

4 As explained earlier, the SS and FF relationships' calculations will be included with the DML calculations but
will not appear to the user because they will be in the background. In other words, the user will only assign a
DML relationship, not a combination relationship.