Checking Data Flow Models for Correct Use of Physical Units

For developing embedded (control) software, graphical modeling languages based on the data flow paradigm are increasingly used, primarily due to the similarity with electronic (or electric, hydraulic etc.) circuit design. Here, software modules or functions, respectively, are essentially graphs with nodes representing operations and edges representing signals (data). Signals often denote values of various physical units like current or voltage, but have to be represented by the same elementary signal (or data) type like "real", making automatic detection of mistakes like adding current and voltage or mixing feet and meters impossible at data type level. This paper describes how such errors can be detected in data flow computational models, keeping the additional workload for the model developer to a minimum. An example implementation for Simulink illustrates the usability of the taken approach, which is therefore an important means for verification of safety-critical software.