Computing and data-intensive applications in physics, medicine, biology, graphics, and business intelligence require large and distributed infrastructures to address the challenges of the present and the future. For example, process mining applications are faced with terrabytes of event data and computationally expensive algorithms. Computer grids are increasingly being used to deal with such challenges. However, grid computing is often approached in an ad hoc and engineering-like manner. Despite the availability of many software packages for grid applications, a good conceptual model of the grid is missing. This paper provides a formal description of the grid in terms of a colored Petri net (CPN). This CPN can be seen as a reference model ...