Creating Useful Models

Consider if you were planning a trip for yourself only and you wanted to create a schedule. Your schedule for such a project is simply a list of tasks that should be accomplished in a particular order. There would be no need for you to create a CPM schedule because you only need to coordinate the project with three people (i.e. me, myself, and I). To make sure you packed and planned properly you may need to consider using a “to-do” list. When explaining your trip to others you may use simple communication tools such as an itinerary.

As the project moves from your personal road-trip to a few friends or a family group planning a vacation trip across country, the types of communication you need to do becomes more difficult. For small groups with simple projects, a calendar may be combined with a to-do list to identify tasks that must be accomplished by a given time. In such projects, once the overall goal is agreed upon it is often left to each individual to complete the tasks assigned to them. Following the assignment of specific tasks prior to the trip, only limited coordination on key milestones, such as airline tickets purchases, need be coordinated. Given the “hard milestone” of getting on the plane, you might assume that each member of the party must have their own bag packed prior to that boarding. Unless you are responsible for children, you will only generally track the progress of other members of your party as they pack. In this type of project there are multiple parallel activities, completed by different “resources”.

Unless the members of your travel party are notorious procrastinators or you encounter major illness or weather events, building projects will generally be much more difficult to plan, communicate, and complete than the projects considered above. To transform empty space into designers’ vision of an engineered environment that may meet an owner’s functional and ascetic requirements groups of trades must move through space and time in sequence to complete their appointed tasks. The schedule must clearly communicate with all parties, from owner to tradesman, what is to be accomplished at what time. Given the differences in the span of control, and overall understanding of the project of each of these diverse parties, you will need to have a schedule that – from the start – is able to identify those aspects of the projects meaningful to each party.

As noted at the start of this tutorial, an effective scheduling technique address both sequence and duration. The specific techniques you have mastered in previous sections of the tutorial provide the techniques of CPM scheduling that describe sequence and duration. Unless you have extensive experience running construction projects, you are unlikely to immediately understand how these techniques are most effectively used to run projects. The sections of this chapter will illustrate ways to use the techniques of CPM scheduling to greatest effect. This chapter begins to hint at the "art" of scheduling that needs to be employed above and beyond the "science" of the CPM technique itself.

Professor Box, a famous statistics professor and author, stated that "all models are wrong, some models are useful." CPM techniques are criticized as being unable to correctly reflect the complexity of the construction site - i.e." wrong". As with Professor Box's statistical models, or any other model, CPM schedules are never meant to exactly predict every event on a jobsite. CPM models may, nonetheless, make models that are extremely useful to all project stakeholders.