Relationship Diagramming Proposed as New CPM Idea

6/5/2006 By Paul Levin in Orlando

The Project Management Institute College of Scheduling held its third annual conference and it appears that the college has evolved into an impromptu think-tank for further product development.

	Plotnick

At the college’s first conference in Montreal two years ago, project planner Scott Herold introduced a multiple float-path software plug-in that Primavera Systems Inc. incorporated into its critical path method scheduling software the following year (ENR 5/17/04 p. 22). At this year’s event, held April 23-26 in Orlando, the college’s technical course director, Fredric L. Plotnick, introduced the concept of the Relationship Diagramming Method (RDM) of CPM scheduling. In the current Precedence Diagramming Method (PDM) approach, certain relationship types between activities can introduce situational inaccuracies and uncertain results in schedule output, he says. For example, there may be a difference between saying, “Activity B may start seven days after the start of Activity A” and saying, “Activity B may start when seven days (or 70%) of Activity A has been completed.” This would be especially true if Activity A were to stall after a reported start date.

Plotnick, who is an engineer and attorney, demonstrated how new relationship-specific elements can be incorporated into the software to more accurately model how activities interact on a construction project, resulting in more meaningful CPM schedules. One major improvement he suggests is to code each restraint as being physical (planning) or resource (scheduling) based, allowing the software to assist in alternate resource allocation.

“In addition to clarifying activity interactions, another advantage RDM provides over PDM is a reduction in time to develop recovery schedules through the use of ‘smart’ relationships,” says Plotnick. Primavera co-founder and Chief Technology Officer Richard K. Faris has committed to incorporating Plotnick’s enhancements into upcoming versions of Primavera Engineering and Construction, perhaps as early as the end of this year.

Atlanta-based cost engineer and software developer Ron Winter also presented his algorithm to extract the as-built critical path of a completed project at the college’s annual conference. By providing a straightforward mathematical process that only requires spreadsheet software and Primavera, he formulated a reproducible method for independently calculating an as-built critical path.

This model could help settle delay claims that routinely result in costly legal battles between owners and contractors and each side’s experts. Many schedule analyses rely on a contemporaneous review of schedule status and events, and delay is most often measured against what was critical at the time of the delay.

Another consultant, Richmond, Texas-based Mike Stone, proposed a simplified schedule specification that relies on mandatory schedule collaboration by owner and contractor. The new method is meant to eliminate some of the longer specifications that protect owners.

(Photo by Michael Goodman for ENR)