Schedule Updating and Project Control - Construction Project Scheduling and Control - page 181

only authorized professionals should be able to do so. This guarantees accuracy of the
data and consistency in holding on to the organization's policy. This also limits the
liability for the integrity of the data before upper management executives. This author
recommends one of two approaches:
1. Project managers and other project management team members can view but
not edit the schedule. Editing must be exclusively the responsibility of the
scheduler.
2. Any project manager can view any project schedule but can edit only his or her
schedule. The scheduler must review all projects, however.
Schedule Comparisons: Some commercial software programs on the market
compare two schedules. For example, Claim Digger (originated by HST Software,
Simpsonville, South Carolina, and later acquired by Primavera Systems) can com-
pare two Oracle Primavera P6 schedules. In this case, you can compare the current
update with the previous (or another) update and summarize changes that happened
between the two updates. You can select all or certain criteria for comparison, such
as added activities, deleted activities, added relationships, deleted relationships, per-
cent complete, used resources, budget, constraints, and so forth. Comparison with the
baseline schedule is still important. It tells you where you stand currently compared
with where you are supposed to be (the baseline), which is—contractually—the bot-
tom line. Nevertheless, comparisons with the previous update are important because
they show whether you are moving in the proper direction.
Sometimes, after step 2 in the updating process (explained earlier) has been com-
pleted, negative total float values appear on the schedule for certain activities. This is a
red flag that must be addressed. A negative float for an activity means that the activity
is behind schedule by a number of days equal to the float amount. There could be one
of two reasons for this:
1. The entire project (primarily, the critical path) is behind schedule. If the nega-
tive float values vary—say, one activity has a total float ( TF )=−12 and another
has a TF =−8, the critical path is the path with the most negative float. 6 This
is the definition of the critical path (the longest path). You may argue that the
activity with TF =−8 is “critical” as well. Oracle Primavera P6 even allows you
to change the definition of critical activities. This issue is discussed further in
Chapter 8.
2. One particular activity is behind its constrained start or finish date. The entire
project may still be meeting its expected completion date. For example, you
could have the milestone Building Dry-in with an early finish constraint date
of 13 OCT 14. If the calculated early finish date is 16 OCT 14, you will have
TF =−3 for this activity. Note that there will be activities with similar negative
float on a continuous path, starting from the data date until that activity.
6 Mathematicians consider −4 greater than −8, but using this notion in construction may be confusing. In
this topic, if we say the “larger” negative float, we mean in terms of absolute value.