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Abstract

Abstract
Early fault detection remains a critical challenge in predictive maintenance (PdM), particularly within critical infrastructure, where undetected failures or delayed interventions can compromise safety and disrupt operations. Traditional anomaly detection methods are typically reactive, relying on real-time sensor data to identify deviations as they occur. This reactive nature often provides insufficient lead time for effective maintenance planning. To address this limitation, we propose a novel two-stage early detection framework that integrates time series forecasting with anomaly detection to anticipate equipment failures several hours in advance. In the first stage, future sensor signal values are predicted using forecasting models; in the second, conventional anomaly detection algorithms are applied directly to the forecasted data. By shifting from real-time to anticipatory detection, the framework aims to deliver actionable early warnings, enabling timely and preventive maintenance. We validate this approach through a case study focused on metro train systems, an environment where early fault detection is crucial for minimizing service disruptions, optimizing maintenance schedules, and ensuring passenger safety. The framework is evaluated across three forecast horizons (1, 3, and 6 hours ahead) using twelve state-of-the-art anomaly detection algorithms from diverse methodological families. Detection performance is assessed using five performance metrics. Results show that anomaly detection remains highly effective at short to medium horizons, with performance at 1-hour and 3-hour forecasts comparable to that of real-time data. Ensemble and deep learning models exhibit strong robustness to forecast uncertainty, maintaining consistent results with real-time data even at 6-hour forecasts. In contrast, distance- and density-based models suffer substantial degradation at longer horizons (6-hours), reflecting their sensitivity to distributional shifts in predicted signals. Overall, the proposed framework offers a practical and extensible solution for enhancing traditional PdM systems with proactive capabilities. By enabling early anomaly detection on forecasted data, it supports improved decision-making, operational resilience, and maintenance planning in industrial environments.

Abstract

Abstract
Context: Software testing is an often used method to ensure software quality, with developers spending a significant amount of time on it. However, software testing education is underrepresented in curricula, particularly with regard to Conceptual Modelling (CM), where model-level validation is important. As a consequence, graduate students are insufficiently prepared for industry-level testing. Objective: We want to understand students' behavioural patterns during model testing and their relationship to testing effectiveness.Method: We use process mining to analyze 554 interaction logs from students using a conceptual model simulation tool.Results: We identify three strategies: the coverage chaser (using feedback iteratively), the problem solver (balancing feedback with requirements focus), and the disconnected tester (avoiding feedback-driven iteration). High-coverage students integrated feedback into test loops; low-coverage students did not. Notably, high and average-coverage students achieved similar grades, suggesting a plateau where systematic testing enables sufficient educational performance without requiring maximum coverage.Conclusions: Our findings highlight the importance of teaching students to systematically use coverage feedback to guide test design in CM contexts.

Abstract