1. Method for operating an installation of a basic industry, using a computer system, wherein products assigned to different production orders are produced in the installation, and wherein a production plan is generated using method steps comprising: a) generating an initial production plan from a plurality of production orders; b) generating a sequence of the production orders stored in the production plan while taking into account process-related restrictions to which the installation and the production orders are subject; c) generating an executable production plan that takes into account the process-related restrictions to which the installation is subject; and d) optimizing the executable production plan generated.