The invention relates to a system for writing a simulation program for simulating an automation installation. To facilitate the writing of a simulation program for a complex automation installation, the system comprises: means for defining a respective resource object for at least two components of the automation installation, means for defining port data for each port, which define characteristics of the values which can be interchanged on the associated port, means for identifying a first port of a first resource object, which is provided for interchanging values with a second port of a second resource object, on the basis of the port data associated with the first and second ports, means for defining precisely one variable which can be engaged with the values to be interchanged between the first and second ports, and means for integrating the program fragments associated with the first and second resource objects into the simulation program and for engaging the variables with the values to be interchanged between the first and second ports.