Four scheduling experts, all deeply experienced in the critical path method (CPM) that uses math to draw network diagrams of a project schedule, met recently in a restaurant just outside Philadelphia. The purpose was to discuss a new unit at the Project Management Institute, in Newtown Square, Pa. The College of Scheduling they have launched would promote "the fundamentals of project management" and encourage "a free exchange of ideas."

One of the reasons for starting the college is disconcerting. What is described as a CPM schedule these days sometimes isn't one at all, the four experts claim. If that claim is true, it says a lot about how personal computers have transformed scheduling and what could be in store as technology reshapes other phases of the construction process.

At the meeting, the four experts lamented the state of scheduling. They say they see widespread abuses of powerful software to produce badly flawed or deliberately deceptive schedules that look good but lack mathematical coherence or common sense about the way the industry works. The result is confusion, delayed projects and lawsuits.

How did this happen? PCs have popularized and democratized CPM schedule writing, which first took hold in construction in the early 1960s, but it has also put scheduling in the hands of many inexperienced and poorly trained practitioners. When they do the work, critics say the basic principals of CPM are sometimes neglected or watered down.

The four men, three of whom are directors of PMI's College of Scheduling, reserved some of their most pointed comments for Primavera Systems Inc., the Bala Cynwyd, Pa.-based company that is the dominant supplier of construction project management and scheduling software. The four men say Primavera puts features in its popular scheduling programs that provide flexibility but are open to abuse.

Primavera's headquarters is about 10 miles from where the meeting took place and its president, Richard K. Faris, is active in industry affairs and is a board member of the new College of Scheduling. Significantly, he had not been invited to the meeting. Faris says the implication is dead wrong that Primavera can control the way its software is used. The company makes a robust and versatile product geared to the needs of its users, he says. Primavera can't be responsible for abuses any more than a spreadsheet company is responsible for those who use its product to draw up faulty or deceptive reports, he contends.

New Way Overshadows Old
Arrow Diagramming Method (ADM)
A once-popular but disappearing method of representing project activities with arrows, with a node shown as a circle, representing events at the ends of the arrows. The tail of the arrow is the beginning and the head represents the completion. While it is less flexible than PDM, it has the advantage of defining the logical relationships between activities entirely by the activity numbers.
Precedence Diagramming Method (PDM)
Developed in the early 1960s into current form by H.B. Zachry in cooperation with IBM, this popular and flexible technique avoids using the dummy activities to maintain logic relationships needed in ADM. It represents activities as boxes that are assigned properties of the activities they represent. Includes the four types of lag relationships: finish-to-start, finish-to-finish, start-to-start and start-to-finish.

These critics "would like us to put in things that make people use the program in a certain way, but people don't want to buy a tool like that," says Faris, who founded the company with partner Joel Koppelman 20 years ago after they had both worked in the construction industry. "People want tools that are flexible, and if they are flexible they can be abused."

With annual sales of $77 million, 85% of it in scheduling software, Primavera is the biggest player in its market niche. Its P3 product, which sells for about $4,000 per concurrent license, is complemented by a simpler $500-per-user product called SureTrak. Competitors include Microsoft Corp., whose product is in the lower range. Meridian Project Systems also acquired technology in 2001 and began offering a CPM scheduling program.

With what it claims is 300,000 scheduling users around the world, Primavera is now answerable to a marketplace far wider than the handful of innovators at universities and corporate labs who gave birth to CPM scheduling. The software company also shapes the way the industry works through its popular product.

In its first decades, critical path method scheduling was the near-exclusive province of full-time project management consultants and construction managers. No longer. Thousands of contractors and many firms in other industries now are using low-cost scheduling software. Calculations that once needed mainframes routinely are performed on desktops.

TOOLS Faris says Primavera provides what users want.
(Photo by Michael Goodman for ENR)

To prevent errors by inexperienced users, one construction manager centralizes planning and scheduling within each company unit. "The new versions that are out are relatively inexpensive and relatively easy to learn, and that leads to the temptation to have relatively inexperienced people doing some of the scheduling," says Dennis K. Bryan, director of scheduling for St. Louis-based McCarthy Co. In doing the work, fundamentals of CPM can be ignored, he says.

"Scheduling has moved away from the priests of scheduling to the common man and there are less knowledgeable people doing it," says Faris. He says training is therefore vital.

Among the four critics who attended the Philadelphia meeting was at least one who qualifies as a scheduling priest. James J. O'Brien, an engineer and CPM pioneer, was the co-founder of O'Brien Kreitzberg (subsequently acquired by URS Corp.). The firm was the oldest and largest specializing in program and construction management. He was joined by Fredric L. Plotnick, an attorney, engineer and consultant who co-authored with O'Brien the latest edition of CPM in Construction Management (McGraw-Hill, 1999). The two other critics were Jon M. Wickwire, a Vienna, Va.-based attorney and consultant who has written extensively on CPM, and Stuart Ockman, a project management consultant based in Wallingford, Pa.

What they have seen they have sometimes described as rotten bananas in a software paradise: flawed schedules produced with powerful new tools.

In particular, the current method of CPM scheduling, Precedence Diagramming Method (PDM) (see chart), which became the de facto standard in the U.S. in the mid-1990s, is open to manipulation and deception, they say. For example, PDM allows users to assign different calendars to different activities, which means if those activities are on the same logic path they won't show up with the same amount of float, the cushion of days in a schedule before a delay can hold up the entire job.

"That's like saying the grass is not green anymore to a classically trained scheduler from the 60s, 70s and maybe early 80s," says Ockman. Although he doesn't blame Primavera, he says, "The fact is that the primary de facto standard has prevented CPM from being practiced the way the inventors created it."

Faris answers that multiple calenders make scheduling more complicated but that users say they want them to match up with the different types of workweeks common today.


O'Brien sent out an alarm to colleagues in 1997. "It appears that Primavera is trying (apparently with great success) to eradicate CPM as we know it," O'Brien wrote. Later, he added, "I have a sci-fi feeling that computers are being used to steal control of the art of planning and scheduling."

That feeling still lingers for O'Brien. "Some people want to wipe out the part of scheduling we grew up with, saying it's all almost can't get a program on ADM, and it's frustrating," O'Brien says. As if to underscore the issue, the latest edition of O'Brien's book comes with a Primavera CD.

Under PDM, activities on a network diagram can be connected from either the activity's start or finish, and lag and lead factors can be used, allowing what some say is a cleaner, clearer diagram. But the logic behind the schedule then is not apparent on its face, as it is with ADM, and that's a step backward, says O'Brien.

Not everyone is displeased. "I think PDM is a much clearer representation of the logic of the schedule" and flow of work, says James L. Jenkins, assistant professor in the Dept. of Building Construction Management at Purdue University, West Lafayette, Indiana. "You know exactly once you finish an activity which activities can start."

One possible disadvantage of PDM involves the display of the time that elapses before the next activity. With PDM's time-scaled display, the information can be hard to read, says Scott Kramer, associate professor in the Building Science Dept. at Auburn University, Auburn, Ala. With time-scaled PDM, the display can start to look like "a plate of spaghetti," and so people often suppress the logic arrows and use the easy-to-read bar chart. "That's what I like about Primavera," says Kramer, who teaches both ADM and PDM.

Nothing epitomizes the changes in CPM scheduling more than the reappearance of bar charts as graphic summaries of the schedules. For many schedule experts raised on ADM, the critical path can't be as readily identified in a bar chart, and its return is one of O'Brien's biggest disappointments. During the recent meeting, he picked up a hand-drawn ADM diagram, something that is little seen any more.

There are other concerns. Instead of being a trustworthy planning tool, some of the new schedules are minefields, say the critics. Wickwire and Plotnick are especially concerned about the options in the software to override or retain logic or impose or remove restraints. One of the problems they see in PDM is automatically making an activity or string of activities critical that may not belong on the critical path, a practice that they claim is anathema to well-trained CPM users.

"The point is, we lose the intellectual rigor and discipline required to properly go ahead and to properly utilize the technique," says Wickwire. A law book he co-authored, Construction Scheduling: Preparation, Liability, and Claims (Aspen Publishers, 2003), is full of examples of schedules being written or altered improperly. In one example from a few years ago, a contractor simply shortened the duration of activities in the later stages of a project when work fell behind on the early phases. But good scheduling practices require monthly updates including performing forward or backward passes through the entire project.

As for the software, all that's needed in some instances are asterisks to draw attention to places where the logic has been overridden, says Plotnick. "Its not the software's fault, but the software company should have something in there so the engineer is given a warning when somebody is misusing it," he says.

Faris agrees that leads and lags can be used excessively, but he says assigned constraints and retained logic both have legitimate uses.

One complaint by O'Brien and others is that polished, easy-to-read graphics are being emphasized over process integrity. That complaint, agrees Russell J. Lewton, construction manager for the Weitz Co. LLC, Des Moines, is right on target. "You must be careful not to be sucked in by the fact that it is a polished-looking schedule because computer schedules can be overwhelming (in size and complexity) when they incorporate too great a level of detail," he says. But if not sufficiently detailed, they are meaningless, he adds.

"Among the young guys, computers have made it easy to slap together something that looks right, but there is a thought process that must be involved, and it is hard to tell in many contemporary schedules if the thinking happened or not," Lewton says. Weitz puts the schedule writer together with the project staff to get "the right detail for the application."


Others say cooperation and how a schedule is prepared and used on the project is more important than errors by schedulers made possible by the software. "The most glaring weaknesses in schedules result from a failure to seek adequate buy-in at the front end," says Joe Wathan, a project director for San Mateo, Calif-based Webcor Builders. But he also says that the tools available in scheduling software are running ahead of the training and resources dedicated to using it. "If you take the Lamborghini scheduling tools on a large project without the resources necessary to manage the tool, we still get the student-driver result," he says.

How PDM Schedules are Abused
Excessive leads and lags:
A lag is the number of work periods by which an activity may be delayed. It may fail to show which part of an overlapping activity is critical or to identify how much must be in place before successor starts.
Makes identifying impact of changes difficult.
Multiple calendars:
May lead to difficult and sometimes anomalous results in calculating project status on updates, as well as overall project duration.
Can lead to discontinuous float paths and make it hard to identify the critical path.
Assigned constraints:
Overrides computer calculations at the core of CPM scheduling.
According to one scheduling expert, "If you do this, it's a bar chart" and not a traditional CPM network diagram and schedule. But the problem exists in degrees, and one assigned constraint is not anywhere near as damaging as 500.
Retained logic:
When used for automatically updating out-of-sequence activities, critics claim it makes it impossible to get an accurate update.
If you don't revise logic when work is out of sequence, you will get erroneous remaining durations because there is no way to know, short of spending much time researching the network, which activities are driving the activities that are currently in progress.
Source: Construction Scheduling: Preparation, Liability and Claims, 2nd Edition

Another phenomena worth noting, says Kent D. Pothast, scheduling manager for Portland, Ore.-based Hoffman Construction Co., is that schedules often are anticipated as tools in claims and lawsuits. As a result, what may have started as a pure construction schedule is written to include owner decisions, architect's timely submittal of drawings, approval processes for changes and other data. The common result, whether float is being added or eliminated, is "you are trying to keep somebody off you or put pressure on somebody else," says Pothast.

Some contractors set up schedules in which anyone else's delay of any kind allows them to file for more time and money. Government agencies are wising up, however. At least one agency now specifies how many activities can be within two weeks of the critical path to stop contractors from putting in semi-artificial activities to get rid of float, says Pothast.

The software programs all do the same thing, he says, and once activities, durations and logic are entered "you can trust the software," says Pothast.

Plotnick wants scheduling to be a branch of engineering, like steel design, so that software is used properly and those who would perpetrate deceptions can be penalized. Others say the only solution is to discourage questionable PDM practices, which is exactly why the College of Scheduling exists. O'Brien says he believes Primavera wants to do what's best for the industry and produces an excellent product. "Like the gun industry, their exceptional product can be put to bad purposes," he says.

Primavera's Faris questions whether the software firm has the responsibility to uphold law and order. His answer: "We have the responsibility to provide a tool that provides correct answers."

A turning point came in 1994, when Primavera switched the platform for its programs to the Windows operating system, which Microsoft uses. When it made the change, Primavera stopped supporting the Arrow Diagramming Method (ADM). Most users had already switched to drawing up their schedules using PDM. A similar dilemma exists for other contractors. A "big and complicated" schedule negates its effectiveness, says Allen P. Read, chief scheduler for Salt Lake City-based Layton Construction Co. For that reason, he avoids resource loading, data on work crews and other things needed for the job, unless he must do so because a public works agency requires it. Some government agencies want to see a lot of specifications and milestones and some even limit the duration of project activities. As result, Read may have to break the activities into components, "adding clutter to the schedule."