RaM: Causally-Connected and Requirements-Aware Runtime Models using Bayesian Learning

Abstract

[Context/Motivation] A model at runtime can be defined as an abstract representation of a system, including its structure and behaviour, which exist alongside with the running system. Runtime models provide support for decision-making and reasoning based on design-time knowledge but, also based on information that may emerge at runtime and which was not foreseen before execution. [Questions/Problems] A challenge that persists is the update of runtime models during the execution to support up-to-date information for reasoning and decision-making. New techniques based on machine learning (ML) and Bayesian Learning offer great potential to support the update of runtime models during execution. Runtime models can be updated using these new techniques to, therefore, offer better-informed decision-making based on evidence collected at runtime. The techniques we use in this paper are based on a novel implementation of Partially Observable Markov Decision Processes (POMDPs). [Contribution] In this paper, we demonstrate how given the requirements specification, a Requirements-aware runtime model based on POMDPs (RaM-POMDP) is defined. We study in detail the nature of such runtime models coupled with consideration of the Bayesian inference algorithms and tools that provide evidence of unexpected/surprising changes in the environment. We show how the RaM-POMDPs and the MAPE-K loop offer the basis of the software architecture presented and how the required casual connection of runtime models is realized. Specifically, we demonstrate how according to evidence of changes in the systems, collected by the monitoring infrastructure and using Bayesian inference, the runtime models are updated and inferred (i.e. the first aspect of the causal connection). We also demonstrate how the running system changes its runtime model, producing therefore the corresponding self-adaptations. These self-adaptations are reflected on the managed system (i.e. the second aspect of the causal connection) to better satisfice the requirements specifications and improve conformance to its service level agreements (SLAs). The experiments have been applied to a real case study for the networking application domain.