Many requirements monitoring approaches have been proposed that check key properties of systems and their interactions at runtime. Some of these approaches also visualize monitoring results and provide details on requirements violations to end users. However, only few studies exist about the usefulness of requirements monitoring tools for practitioners, particularly regarding visualization. In this paper, we present a user study we have conducted with both industrial practitioners and researchers to assess the usefulness of visualization capabilities we have been developing for an event-based requirements monitoring tool. These capabilities allow users to monitor the status of the involved systems, to view trends and statistics, and to inspect the events and data that led to specific violations when diagnosing their root cause. We first performed a walkthrough of the tool using the cognitive dimensions of notations framework from the field of human-computer interaction. We then conducted a user study involving five software engineers of a large company from the automation software domain and four researchers. Using the tool's visualization capabilities all subjects succeeded in monitoring a real-world automation system and in diagnosing violations. Subjects regarded the visualization capabilities as essential for understanding the behavior of a complex system. Based on the study results we derive implications, opportunities, and risks of using visualization in requirements monitoring tools.

Industrial software systems are often systems of systems (SoS) whose full behavior only emerges at runtime. The systems and their interactions thus need to be continuously monitored and checked during operation to determine compliance with requirements. Many requirements monitoring approaches have been proposed. However, only few of these come with tools that present and visualize monitoring results and details on requirements violations to end users such as industrial engineers. In this tool demo paper we present visualization capabilities we have been developing motivated by industrial scenarios. Our tool complements ReMinds, an existing requirements monitoring framework, which supports collecting, aggregating, and analyzing events and event data in architecturally heterogeneous SoS. Our visualizations support a `drill-down' scenario for monitoring and diagnosis: starting from a graphical status overview of the monitored systems and their relations, engineers can view trends and statistics about performed analyses and diagnose the root cause of problems by inspecting the events and event data that led to a specific violation. Initial industry feedback we received confirms the usefulness of our tool support. Demo video: https://youtu.be/iv7kWzeNkdk..