Context-aware systems are widespread in our daily lives, but modeling languages that address the notion of context are rare.
Variable structure systems (VSS) allow for structural and behavioral changes in physical models at runtime (while the simulation is running) based on different situations.
It is desirable to explicitly describe under which contextual situation a specific variant of the simulation model should be used and how to implement the switching between these variants at runtime.
In this case, contexts could be used to control the variability of context-aware systems.
Equation-based modeling languages are suitable for modeling complex multi-domain, multi-physical systems, and among them, Modelica is the state-of-the-art.
Unfortunately, the capabilities for VSS in Modelica are strongly limited.
As a result, several frameworks have been proposed to address this problem by supporting different VSS types.
However, it remains unclear which framework contributes to which VSS type.
Furthermore, approaches have been developed to support VSS, but none can explicitly describe contexts and their transitions.
In this work, we first introduce VSS and its different types.
Then, we provide an overview of which framework targets which VSS type.
Finally, we propose a new language extension based on Modelica, ContextModelica, that provides semantics for the direct context definition, enabling the use of context to control and manage variability.