Engineering applications are determined by an increasing importance of their software components. The high complexity and demands for safety of current engineering systems require the development of methodologies which put together formal techniques used in the engineering and computer sciences. To meet this requirement, the DFG (German Research Council) has launched the priority programme "Integration of Software Specification Techniques for Applications in Engineering". This abstract describes some results of the project KNOSSOS, one of the fourteen research projects in the programme, and focuses on the integration of the specification languages Petri nets and \sc Troll. The project has two main research directions. The first one is the development of an integrated approach to the modeling of engineering applications using both specification languages. This includes, on the one hand, their integration in the description of the different system views, and on the other hand, finding out the relation between their language constructs. To put the integration approach into a concrete form, a case study has been modeled. The second research direction consists in the development of a meta model which relates the notations and their possible interpretations in the application domain. In this paper, we concentrate on the integration concept and show its application in the modeling of a simplified version of the case study.