Other Scheduling Methods - Construction Project Scheduling and Control - page 324

restraints), the early finish may be later than the early start plus duration.
Many software products assume that a project manager will not deploy
resources until they may be used continuously and without interruption
and, therefore, that the software will recalculate the early start as being
equal to the early finish minus the stipulated duration. When this is done,
and is not understood by the user of the software, issues will occur when
such an activity is connected to yet another by a SS (start-to-start) restraint,
which will be based upon the new, delayed early start. While this mode
of calculation may be shut off by a system setting in some software, the
choice really should be on an activity-by-activity basis. A third option is to
recalculate the duration as being EF − ES and adjusting resource usage by
DUR old /DUR new .
c. M/R/P (Modified/Retained/ProgressOverride Logic): Where an activity
has been performed out of sequence, there have (in some software prod-
ucts) been two options for how to calculate the schedule of started-but-
not-finished and subsequent activities. The first option is named retained
logic . Here, the original logic is used to schedule the remaining work on the
started activity. Therefore, continued work on the started activity may not
occur until after all predecessors of this activity have been completed. The
second, named progress override , is to assume that if an activity has started
out of sequence, it will most likely continue through the completion and
that subsequent activities may also then continue without regard to the
uncompleted predecessors of the out-of-sequence activity. Current software
offerings either lock into one of these two calculation models or provide
a system option for all activities. RDM provides the choice of option for
each activity and also provides a third option (which is the default setting).
This third option is called modified logic , which schedules the continuation
of the started-but-not-finished activity on the data date but creates a FF
(finish-to-finish) restraint on the finish of the activity from the finish of all
predecessors to that activity (similarly to the retained logic option).
d. Calendar—Shift/Hourly—RDM recognizes that a shift is a discrete time
unit and not merely (any) 8 hours. An activity of original duration of
10 days reported 35% complete will calculate a remaining duration of 7
days and not 6-1/2 days. Similarly, an activity with 5 days duration but
on a two-shifts-per-day calendar, will then push a successor activity on a
one-shift-per-day calendar to start at the beginning of the third day.
3. Restraint types : RDM recognizes several additional restraint types to the stan-
dard PDM choices of FS, SS, FF, and SF (finish-to-start, start-to-start,
finish-to-finish, and start-to-finish, respectively). These include a PS
(progressed-to-start) and FR (finish-to-remainder) restraint, as well as
several other specialty restraints beyond the discussion of RDM in this text.
RDM recognizes a distinction between a restraint measuring time elapsed
from the calculated or reported start of an activity to the start of another