Enforcing model composability in Modelica

Modelica provides intuitive constructs to create and group model definitions. However, models themselves do not compose. In other words, the connection of type-compatible and locally balanced submodels does not generally yield a valid (e.g., balanced, structurally non-singular) model. Starting from simple examples of such invalid models (resulting from commonly encountered situations when using Modelica), this paper explains how those problems could be avoided by introducing a safer notion of physical connector, similar in some aspects to the VHDL-AMS notion of terminal. An extension of the notion of connection is also presented, providing new opportunities to make efficient use of ideal models in Modelica.