||In recent years several new modeling approaches have been published to cope with the increasing complexity of software systems. Thereby model integration was widely neglected, which led to heterogeneous modeling approaches. In this work we define the basic modeling terms and compare research projects in the domain of modeling and model integration. To identify current modeling problems, we carried out a case study using the heterogeneous modeling approach “Processes with User Interfaces and Data Modeling Integration” developed at Software Competence Center Hagenberg GmbH (SCCH). This modeling approach consists of four views and several abstraction levels. The identified issues, however, are not only relevant for this modeling approach but represent general problems like granularity, model consistency, traceability of changes, model integration, versioning, and the selection of modeling tools. These challenges are described and serve as foundation for an ongoing research project at SCCH on modeling and model integration.