Theory of Constraints Handbook - James Cox Iii [18]
Purpose and Organization of the Chapter
The overarching purpose of this chapter is to expose the problems associated with “traditional” project management. Specific solutions are not to be found here, but rather what is provided is a framework for developing a new project management method that uses a systems perspective to address the core problems of traditional project planning, scheduling, and controlling tools. A systems perspective is needed to fully assess the impact of an assumption related to an activity, to resource contention, or to converging paths on the results of a project.
Copyright © 2010 by Ed Walker
To accomplish this task, first the reader will be provided with brief overviews of both Gantt chart scheduling and PERT/CPM. Gantt charts were first developed nearly 100 years ago, while PERT (initially named Program Evaluation Research Task and later changed to Program Evaluation and Review Technique) and CPM (Critical Path Method) began their evolution approximately 50 years ago. Each of these methods has both advantages and disadvantages, which are summarized. Brief reviews of the literature related to the origins of project management and the high failures of projects since its origin, as well as literature related to both single and multiple project networks and resource allocation are then presented. The main body of the chapter is devoted to the development of guidelines that any new project management method must address. This is followed by a brief introduction to Critical Chain Project Management (CCPM) and finally a review of the recent CCPM literature.
Traditional Planning and Control Mechanisms in Project Management
Gantt Charts
A Gantt chart is a horizontal bar chart developed as a production control tool in 1917 by Henry L. Gantt, an American engineer and social scientist. Frequently used in project management, a Gantt chart provides a graphical illustration of a schedule that helps to plan, coordinate, and track specific activities in a project. These charts might be as simple as a hand-drawn image on graph paper, or as complex as purpose-built computer software. A simple Gantt chart used for a project is shown in Fig. 2-1.
The horizontal axis of the chart represents the total time span of the project (broken down into uniform time increments—days, weeks, months, etc.), while the tasks comprising the project are on the vertical axis. Horizontal bars are used to illustrate the start and end dates of individual activities (for example, task A has a duration of y days starting on day 1 and ending on day 5). In its simplest form, the Gantt chart shows all of the activities necessary to complete the project. Some of the activities must be completed in a specified sequence, while others might progress concurrently. Tasks B and C are processed sequentially and tasks B and D can be processed concurrently. One cannot start framing a home before the foundation is laid; but once framing is complete, the plumbing and electrical systems can be installed simultaneously.
More complex Gantt chart scheduling is often based on a work breakdown structure (WBS). To continue the previous example, the installation of the electrical system (the objective) might be broken down into manageable elements such as the installation of the breaker panel, pulling electrical wires through the home, pulling data cables, connecting the electrical wires to the breaker panel, inspection of the system by the building inspector, etc. It is then necessary to determine the start and end dates as well as responsibility for each. In such a chart, percent completion is tracked for each element and the objectives. A vertical line on the chart shows the current date (March 25) while the completed and noncompleted portions of each horizontal bar are shaded differently to allow visual inspection of the project’s progress. For example, task B is late by two days and task D is early by one day.
FIGURE 2-1 Simplified Gantt