Modeling Event Stream Hierarchies with Hierarchical Event Models

Compositional scheduling analysis couples local scheduling analysis via event streams. While local analysis has successfully been extended to include hierarchical scheduling strategies, event streams are still flat. In this paper, we generalize the concept of a stream hierarchy to embed different types of streams in a higher level structure. We explain why this extension is a natural match to model streams generated by communication stacks that are ubiquitous in networked embedded systems. We formally define the hierarchical event model and give operations to encode, combine, and extract stream properties that can be used in flat or hierarchical local scheduling analysis. Finally, we give an example and demonstrate that the proposed model enables superior analysis results.