Point-to-point Versus Traditional Precedence Relations for Modeling Activity Overlapping

Precedence Diagram Method (PDM) has been the prevailing scheduling technique for decades. This popularity is due to its modeling flexibility over other techniques and the easy-to-understand mathematical model behind the technique. However, even this technique has its own limitations; modelling overlapped activities in a proper way seems to be a never-ending debate. The reason of this can be found in the fundamentals of PDM technique; the four precedence relationships, and the activities that are assumed to be continuous with constant production speed. These fundamentals of PDM have their own consequences to scheduling practice and it is more and more apparent among professional planners that activity overlapping cannot be modeled adequately. Different solutions were proposed for solving this problem from the application of negative lag, through the combination of SS and FF relations to activity fragmentation. All these solutions have their shortcomings. Probably the fragmentation technique has led to the development of point-to-point type of relation that can connect any arbitrary points of the dependent activities. The objective of this paper is to analyze the pros and cons of different solutions are in use for modeling overlapped activities. The main finding of the paper is that newly developed point-to-point relations are better from theoretical and practical point of view than the solutions based on traditional precedence relationships, but they still cannot provide theoretically perfect solution.