Other Scheduling Methods - Construction Project Scheduling and Control - page 318

for example, MATLAB ® , can be set up manually to perform calculations and draw
linear schedule diagrams that can be updated during the project's execution.
Graphical Path Method (GPM) 8
The graphical path method (GPM) was developed by Dr. Gui Ponce de Leon as
an alternative to database-driven CPM models. Rooted in robust mathematics,
GPM algorithms enable graphical, synchronous, and interactive tools that facilitate
hands-on, real-time scheduling. A GPM application lets users plan and schedule
simultaneously, allowing them to carry out resource leveling, schedule optimization,
and time/cost trade-offs as the network is built and the schedule is generated.
The goal of GPM is to transform conventional planning and scheduling into an
engaging, planning-dominated experience for project stakeholders. This method
posits a number of new concepts: planned dates, float, drift, gap, buffer, proportional
link offsets ,and forensic total float . They are briefly introduced in this summary.
In GPM, planning proceeds by drawing a graph of logically related, dated objects
( activities , milestones ,and benchmarks ) into a time-scaled project network model. At
the core of this model is LDM (logic diagramming method), a blend of both PDM
(precedence diagramming method) and ADM (arrow diagramming method). In a
way, LDM resembles a time-scaled version of ADM that allows for PDM overlapping
logic. Start-to-start (SS), finish-to-finish (FF), and start-to-finish (SF) logic is accepted
through embedded nodes , placed in between or directly on an activity's start or finish
nodes. Figure 11.21 shows an LDM schedule for a sample project.
From links and object dates, GPM continually calculates gaps for all links and float
attributes for dated objects. GPM allows activities to be placed on any date between
their early and late dates, and this date is referred to as a planned date .Gapsarethen
calculated from the dates of the two connected activities, and floats, drifts, and total
floats are algorithmically calculated from gaps. An activity that slips and/or extends to
later dates without causing an overrun of project completion (or deadline) has float.
An activity that backslides and/or extends to early dates without causing an earlier
project start (or interim release date) has preceding float, or drift . An activity that has
neither float nor drift is critical . For every object, float plus drift is a constant equal to
CPM total float. In other words:
• Float measures the extent that a positive-drift activity may be delayed beyond
planned dates while not extending the project completion date or an interim
required completion date, and is equal to (Late finish date - Planned finish
date).
• Drift measures the extent that an activity may gain schedule while not forcing
an earlier project start or interim release date, and is equal to (Planned start
date - Early start date).
8 This section was mainly written by the method developer, Dr. Gui Ponce de Leon.