The invention relates to the modeling of a complex system wherein units such as data and/or products are received, processed and forwarded in event chains of the system. Said modeling uses a defined set of basic types at the lowest description level for representation of the units and in order to describe the interaction therebetween. Each basic type processes data representing values of characteristics of the above-mentioned units. The set of basic types comprises a basic type known as forward, which represents the forwarding of the units, conducts data for the characterization of said units and is provided with an input and an output; a basic type known as merge which represents a combination of units, combines data for the characterization of said units and which has two inputs and one output; and a basic type known as divide which represents a fractionation of units, determines data for the characterization of units which arise from a fractionation from data of a unit that is to be fractionated and has one input and two outputs. Inputs are used to receive data from and outputs are used to transfer data into the respective basic group. Computer-based data-processing models of the system are created by forming a number of basic types and by combining the inputs and outputs of said basic types.