The work presented in this paper targets the software integration on the level of business process models. The goal is to create the behavioural description of an integrated system that is consistent with the behavioural descriptions of the original local systems intended to be integrated. We build the behavioural description from existing models of the local systems by inserting dependencies between them. By this means, simulation and verification of interactions between them is possible and incompatibilities can be identified at an early stage before a new system is introduced. So far, business process modelling languages have mainly focused on a single application system although B2B and enterprise application integration demand on models to express cross organisational communication and inter-process dependencies. In this paper, we investigate commonly used business process languages on their suitability to model inter-process dependencies. The result shows that there is no language which supports all identified dependencies directly and that all languages demand from the modeller to consider their low-level semantics which prevent him from focusing on the design. We propose a set of extensions of UML 2.0 Activity Diagrams to overcome these limits.