1. A method for modeling a change in a complex system using comparison of computer-based, data-processing models of the complex system, the method comprising the following steps: comparing a first model and a second model and determining predefined objects of the first model and the second model, wherein the predefined objects are associated with one another in the first model and the second model, wherein the first model and the second model of the complex system are present, and the models in each case model a system behavior by way of the predefined objects that represent activities and units within the complex system; determining differences in attributes of the predefined objects associated with one another in the first model and the second model; and issuing, by a computer, the determined associations of the predefined objects and differences of the predefined objects to a user; wherein at least two models of a same system exist, the first model represents the complex system in a first condition and the second model represents the complex system in a second condition, and comprising the step of a comparison algorithm determining actions for conveying the complex system from the first condition into the second condition is carried out; wherein the modeling of the change in the complex system on a lowermost description level applies a limited set of the basic types representing the units within the complex system and describing the units within the complex system interaction, wherein each basic type processes data, said data representing values of characteristics of the units mentioned, and wherein the set of the basic types comprises: a basic type “transfer”, which represents a transfer of units, leads through data for characterizing these units, and comprises one input as well as one output, a basic type “merge”, which represents a combining of units, links data for characterizing these units to one another, and comprises two inputs as well as one output, a basic type “split”, which represents a division of units, determines data for characterizing units, which come from a dividing-up from data of a unit to be divided up, and comprises one input as well as two outputs, wherein in each type of the basic types, inputs serve for receiving data into respective basic types and outputs serve for transferring data out of respective basic types, and wherein the computer-based, data-processing models of the complex system are formed by way of forming a Quantity of basic types and by way of linking inputs and outputs of the basic types; thereby modeling the change in the complex system.