Overview Planning and scheduling as we know it today has been around since the early 1900’s. Henry Gantt introduced the first bar chart in 1910, and in the late 1950’s, Kelley and Walker…
Under the Hood: A revolutionary scheduling algorithm.
The Graphical Path Method is an innovative scheduling algorithm that serves as an alternative to the Critical Path Method. GPM's unique framework promotes rapid, collaborative, and informed project planning; allows schedules to be created more naturally and intuitively; and introduces previously undefined concepts that improve schedule optimization and analysis. These and several other innovations are what make GPM uniquely suited for a variety of project management applications.
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Discover GPM Features
Image: a network being updated as an activity is moved. Highlighted in blue: durations, link gaps, and total floats.
Real-time Calculations
When an activity is moved within a network, the logic of its relationships breaks down. GPM heals these relationships in real-time by propagating the change throughout the network. This automatic correction is known as ‘self-healing’ and the result is real-time preservation of logic. In addition, since GPM doesn’t rely on a database-driven scheduling engine, dates, durations, float attributes, the critical path, and resource profiles all continuously refresh as the network is modified. These real-time calculations provide invaluable information as schedules are built.
Planned-Dates
GPM omits the early start bias inherent in CPM networks, permitting activities to be scheduled anywhere within their total float range, without constraining float. GPM accomplishes this with the introduction of Drift: the number of time units an activity can gain before advancing the start of the project. In a GPM network, Drift plus GPM Float is equivalent to CPM total float. This new flexibility in planning unlocks possibilities not previously available in CPM. With the ability to plan from either end of the project, a schedule can come together more naturally and intuitively.
Image: Ext. Mason Walls shown in between early dates and late dates without a constraint. Highlighted in blue: link gaps, total floats, & drift and float.
Image: Joists & Desk completed with 1 day of forensic float. Highlighted in blue: link gaps, total floats, & forensic total float.
Forensic Float
In CPM, the ability to calculate floats is lost when actual dates are entered. Not only does GPM retain this ability, but it’s inherent to the GPM algorithm. Once activities are actually completed, floats are interpreted as hypothetical: how much could the activity have been delayed? In GPM, this value is referred to as forensic float, and it continues to update even as activities are modified to the right of the data date. This can be particularly useful when analyzing a schedule for delays after the project has started or finished.
Compare Scheduling Methods↑
| Features | Critical Path Method | Graphical Path Method |
| Diagramming Method | Precedence Diagramming Method | Logic Diagramming Method |
| Activity Placement | CPM Early Dates | Early or Planned Dates |
| Link Leeway Calculation | None | Gap |
| Activity Early Dates | Calculated from Forward Pass | Current Dates Less Drift |
| Activity Late Dates | Calculated from Backward Pass | Current Dates Plus Float |
| Activity Free Float | CPM Free Float | GPM Buffer and Drift-Buffer |
| Can Activity Float Forward? | If Activity Total Float is > Zero | If Activity Float is > Zero |
| Can Activity Float Back? | No, Activity Drift Does Not Exist | If Activity Drift is > Zero |
| Floating by Delaying Start | Reduces Total Float | Does Not Reduce Total Float |
| Float Governing Technique | Through Mandatory Constraints | Benchmarks as Fixed Events |
| Total Floats Left of Data Date | Cannot be Determined (Always = Zero) | Recalculated if Schedule Changes |
| Software Data Structure | Database | Objectbase |
| Scheduling Algorithm | CPM Block Scheduling Algorithm | Step-wise Algorithm |
| Software User Interface | Batch (Multiple Engines) | Interactive, Real-time |
This comparison table is an excerpt from the CPM to GPM Bridge presentation. You can read about and download this presentation here.
Explore GPM Resources↑
CPM to GPM - Easing the Transition
What are the differences between GPM and CPM terminology?
GPM and CPM share some similar concepts. However, some of these concepts are referenced by different terms in one framework vs. the other. Continue reading to view a table that highlights the different…
GPM and Forensic Total Float
In this paper, presented at the 2010 PMI Global Congress Conference, PMA Consultants’s Dr. Gui Ponce de Leon weighs the advantages and disadvantages between CPM and GPM’s use as an analytical tool in Forensic…