Extending RTLola with External Data Queries

Summary

Stream-based monitoring enables the concise specification of complex temporal properties. However, existing stream-based monitors are limited when dealing with large external data sources, a task that is better handled by specialized data management systems. We address these limitations by extending stream-based monitors with the ability to query external data sources. We implement this approach in RTLola and investigate challenges such as handling delayed responses, type checking of returned data, and runtime error management. A unified interface enables the seamless integration of existing systems into our approach, such as static databases or dynamic endpoints, e.g., a weather API. Our evaluation shows that accessing data through custom data structures is beneficial, as it results in improved runtime performance. Our extension decouples the specification from the underlying data representation, allowing the data structure to be optimized independently of the specification.