Real-time Stream-based Monitoring

We introduce RTLola, a new stream-based specification language for the description of real-time properties of reactive systems. In real-time applications, data arrives at varying rates and in most cases it is hard to predict the input rate. The integration of sliding windows over real-time intervals with aggregation functions into RTLola allows us to detach fixed-rate output streams from the varying rate input streams. However, the number of input values within a single window instance can grow arbitrarily large disallowing any guarantees on the expected memory consumption. A feature of RTLola is that it allows for an automatic memory analysis that guides the user in identifying the computationally expensive specifications. For specifications using only certain classes of aggregation functions, we can give a precise memory bound. Furthermore, assuming a fixed monitor output rate, we can provide memory guarantees which can be computed statically. To demonstrate the features of RTLola, we evaluate the language and the implementation experimentally.