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Response to “What is a Project Schedule?”

We want to thank the authors of “A Call to Action: What is a Project ‘Schedule?’” which appears on MPUG’s websiteand all those who provided comments to it (albeit, we would have preferred input that was in the context of the standard). The extraction of a single term out of the context of a developed document provides at best a stilted perspective. We must point out that the comments below are our own as professionals and don’t reflect any position taken or sanctioned by PMI.

For the most part, we feel your comments are in basic agreement with the intent of the standard. In some cases, there appears to be violent agreement. We’ll endeavor to show the areas of agreement in this response.

First, we feel that we all agree that a model is created and it represents the effort to be performed on a project to accomplish the project’s objectives. We believe that all interested parties agree that a model is being utilized. How to bring the term “model” — or not — into the language of the profession is where the various parties involved in the debate differ. Some suggest “project execution model” while others remove the term “model” altogether (“project schedule”). The term introduced in the PMBOK Guide, 3rd Edition, and used in PMI Standards since the 3rd edition, is “schedule model.”

Second,we also agree that this model is dynamic and constantly changing.

Third,we agree that from this model we produce various reports and presentations that the project team uses to manage the project, communicating its status. The example of due dates that you provide as a “schedule” is really an output of a schedule model — what we call a presentation.

Fourth,we agree that there needs to be a model of various aspects of the project execution and various outputs from that model. The question posed in the article parallels one posted by Mike Mosley on November 19, 2004, “Something Easy — Define “Schedule” in the forum “PMI Practice Standard for Scheduling” at The PMI College of Scheduling Forums. The opening of the 2004 post read:

We are all professionals in project management and scheduling. This is true of PMI, the College of Scheduling (now Scheduling Community of Practice), and other organizations. With a depth of knowledge and experience going back to the founding of the modern profession in the late ’50’s, you would think that defining schedule would be easy and almost unnecessary. Nothing could be further from the truth.There is Webster, the PMBOK Guide glossary, legal interpretation, and common usage, coupled with great passion about what is “right.” Over the last year and especially since July, there has been a lot of dialog and debate about the term and the concepts it is intended to represent.

PMI has been in existence for 35 years and is the preeminent authority on project management. The first Guide to the Project Management Body of Knowledge was published in 1987 and had a definition for schedule. The term was most recently updated in the Guide’s 3rd Edition, just published in October. The evolution of the term has progressed as follows:

1987 PMBOK – “Schedule — A display of PROJECT time allocation.”
1994 PMBOK Guide — “Project Schedule — The planned dates for performing activities and the planned dates for meeting milestones.”
2000 PMBOK Guide — unchanged
PMBOK Guide, 3rd Edition — “Project Schedule {Output/Input}. The planned dates for performing schedule activities and the planned dates for meeting schedule milestones.

In the context of project management and the effective planning and execution of projects, this seemed to be unsupportive and significantly lacking. It essentially related to a train or airline schedule much more than to the planning tool we need. The 3rd Edition partially recognized this weakness and added another term, the “schedule model.”

The history and documentation of the term schedule brings into question what is “old school” and when was a schedule first termed as a model, for the “old school?”

We would like to present an accurate sequence of events regarding the introduction of the term “schedule model. It was, in fact, first introduced in the PMBOK Guide, 3rd Edition (publication 2004) in multiple sections, including section “6.5.2, Schedule Development: Tools and Techniques” and “6.6.3 Schedule Control: Outputs.” The first edition of the Practice Standard for Scheduling was chartered after the publication of the PMBOK Guide, 3rd Edition. The Call to Action articles assertion is that “the idea that the project schedule models the project execution does have its detractors, because the term “schedule model” has invaded the epicenter of project management culture and thought — the PMBOK Guide in its 4th edition, which appeared in 2008. It invaded the PMBOK after the term was first inserted in the first edition of the Practice Standard for Scheduling that was released in 2007.” While we believe that the term “invaded” seems to be inappropriately used and the timeline to be off a little, we agree that a term that offers an opportunity for specificity was needed and is being increasingly used within the industry.

In fact, the term Schedule Model is not only introduced in the PMBOK Guide, 3rd Edition, it is also defined in the Standard’s Glossary:

Schedule Model [Tool]. A model used in conjunction with manual methods or project management software to perform schedule network analysis to generate the project schedule for use in managing the execution of a project. See also project schedule.

There may have been some confusion that “The term “schedule model” isn’t actually defined in the exposure draft of the Practice Standard for Scheduling (2nd edition).” A standard’s Glossary is not normally exposed in the PMI public exposure draft (although this could change in the future). The term “schedule model” was defined in both the first edition of the Practice Standard and will appear again the 2nd edition. The committees for both the first and second editions of the practice standard have taken on the challenge to clarify this term and all terms specific to project scheduling.

Although the PMBOK Guide leads us, we have discussed with many practitioners and verified that the differentiation of terms is critical and are an important part of the standard. This is the definition as it appears in the draft of the 2nd edition:

Schedule Model [Tool]. A dynamic representation of the plan for executing the project’s activities developed by the project stakeholders applying the scheduling method to a scheduling tool using project specific data such as activity lists and activity attributes. The schedule model can be processed by a scheduling tool to produce various schedule model instances. (Scheduling Method plus Scheduling Tool plus Project Specific Data equal Schedule Model) SEE ALSO Project Schedule

At the center of the debate surrounding “Schedule Model” is this basic difficulty: Finding a single term that encompasses the range of project documents ranging “from the simplest (activity listing or timetable), to the more comprehensive (bar charts which mesh action with time), to the most complex (network-based schedules, such as CPM, where activities are causally linked.)”

The documented debate began with the PMBOK Guide, 3rd Edition committee (which resulted in a definition), was addressed by both committees for the Practice Standard, and was publicly reviewed in four separate exposure drafts on PMI.org.

We believe, however, that the dialogue and debate regarding “Schedule Model” has moved forward in the profession. We further believe that the term is now part of the language. This is a good example of how the profession is evolving, and its language is evolving.

As a responder to your article stated:

Recently an article in “Project Times” questioned the use of the term “schedule model” instead of just “schedule” or “project schedule” in the Practice Standard for Scheduling. After reviewing the standard, in particular Figure 1.1 and the accompanying text, I believe that the term “model” is used correctly and would have no objections to retaining it in for any future revision of the standard.

Having done mathematical modelling and simulation of complex physical systems for many years earlier in my career, I found that a similar concept appears to have been adopted for the practice standard. That is, the model comprises a set of rules (as embodied in the scheduling method and tool) and a set of data to be manipulated by the rules, that in turn produces the output which is the actual schedule. If the data manipulated by the model changes, the schedule (output) will be different. Similarly, different methods or tools will change the model and, in most cases, the schedule.

The distinction between “schedule model” and “schedule” is quite clear where a sophisticated methodology such as critical path scheduling is being used, since the “model” embodies a fairly complex set of rules operating on a large set of data. Where a much simpler method — e.g. a table of activities and predicted dates pulled out of the air — is used, the distinction is probably moot since any “model” is largely intuitive.

We strongly believe that to revert to a term that was found lacking in its description of a true “schedule,” in all its potential permutations, is a step backward for the profession.

Finally, we believe that the term “schedule model” represents the full range of these potential permutations and better addresses the question, “What is being requested when someone wants to see the schedule” It could be a broad range of products. While some clients or project stakeholders may seek a simple table of due dates, we, as project managers and schedule analysts, usually expect much more.

Written by Charlie Follin

Charles Follin, PMP, is President of ProjectAide based in Decatur, AL. Reach Charlie at ctf@projectaide.com.

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1 Comment
  1. All of my years of experience suggest that virtually all schedules are models since they are a representation of one plan of many. Never does a model and reality directly coincide. As a professional, we understand this intuitively. However, not all users of schedule data are sufficiently experienced in the realities of scheduling and the execution of a plan. I would not be opposed to using the term “schedule model” if for no other reason that to inform the ignorant that is what’s before them. Although it is better today than perhaps 10 years ago, I still work with some project managers that have yet to figure this out.


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