Computing and data intensive applications in physics, medicine, biology, graphics, and business intelligence require large and distributed infrastructures to address today's and tomorrow's challenges. For example, process mining applications are faced with terrabytes of event data and computationally expensive algorithms. Increasingly, computer grids are used to deal with such challenges. However, despite the availability of many software packages for grid applications, a good conceptual model of the grid is missing. Grid computing is often approached in an ad-hoc and engineering-like manner.