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Publications

  • Ulrike Kuhl, André Artelt, Barbara Hammer " Let's go to the Alien Zoo: Introducing an experimental framework to study usability of counterfactual explanations for machine learning"

    Introduction
    To foster usefulness and accountability of machine learning (ML), it is essential to explain a model's decisions in addition to evaluating its performance. Accordingly, the field of explainable artificial intelligence (XAI) has resurfaced as a topic of active research, offering approaches to address the “how” and “why” of automated decision-making. Within this domain, counterfactual explanations (CFEs) have gained considerable traction as a psychologically grounded approach to generatepost-hocexplanations. To do so, CFEs highlight what changes to a model's input would have changed its prediction in a particular way. However, despite the introduction of numerous CFE approaches, their usability has yet to be thoroughly validated at the human level.

    Methods
    To advance the field of XAI, we introduce the Alien Zoo, an engaging, web-based and game-inspired experimental framework. The Alien Zoo provides the means to evaluate usability of CFEs for gaining new knowledge from an automated system, targeting novice users in a domain-general context. As a proof of concept, we demonstrate the practical efficacy and feasibility of this approach in a user study.

    Results
    Our results suggest the efficacy of the Alien Zoo framework for empirically investigating aspects of counterfactual explanations in a game-type scenario and a low-knowledge domain. The proof of concept study reveals that users benefit from receiving CFEs compared to no explanation, both in terms of objective performance in the proposed iterative learning task, and subjective usability.

    https://doi.org/10.3389/fcomp.2023.1087929
  • Kleanthis Malialis , Christos G. Panayiotou, Marios M. Polycarpou, "Nonstationary data stream classification with online active learning and siamese neural networks"

    We have witnessed in recent years an ever-growing volume of information becoming available in a streaming manner in various application areas. As a result, there is an emerging need for online learning methods that train predictive models on-the-fly. A series of open challenges, however, hinder their deployment in practice. These are, learning as data arrive in real-time one-by-one, learning from data with limited ground truth information, learning from nonstationary data, and learning from severely imbalanced data, while occupying a limited amount of memory for data storage. We propose the ActiSiamese algorithm, which addresses these challenges by combining online active learning, siamese networks, and a multi-queue memory. It develops a new density-based active learning strategy which considers similarity in the latent (rather than the input) space. We conduct an extensive study that compares the role of different active learning budgets and strategies, the performance with/without memory, the performance with/without ensembling, in both synthetic and real-world datasets, under different data nonstationarity characteristics and class imbalance levels. ActiSiamese outperforms baseline and state-of-the-art algorithms, and is effective under severe imbalance, even only when a fraction of the arriving instances’ labels is available. We publicly release our code to the community.

    https://www.sciencedirect.com/science/article/pii/S0925231222011481
  • Stelios G. Vrachimis; Demetrios G. Eliades; Riccardo Taormina; Zoran Kapelan; Avi Ostfeld; Shuming Liu; Marios Kyriakou; Pavlos Pavlou; Mengning Qiu; and Marios M. Polycarpou, "Battle of the Leakage Detection and Isolation Methods"

    A key challenge in designing algorithms for leakage detection and isolation in drinking water distribution systems is the performance evaluation and comparison between methodologies using benchmarks. For this purpose, the Battle of the Leakage Detection and Isolation Methods (BattLeDIM) competition was organized in 2020 with the aim to objectively compare the performance of methods for the detection and localization of leakage events, relying on supervisory control and data acquisition (SCADA) measurements of flow and pressure sensors installed within a virtual water distribution system. Several teams from academia and the industry submitted their solutions using various techniques including time series analysis, statistical methods, machine learning, mathematical programming, met-heuristics, and engineering judgment, and were evaluated using realistic economic criteria. This paper summarizes the results of the competition and conducts an analysis of the different leakage detection and isolation methods used by the teams. The competition results highlight the need for further development of methods for leakage detection and isolation, and also the need to develop additional open benchmark problems for this purpose.

    https://ascelibrary.org/doi/full/10.1061/%28ASCE%29WR.1943-5452.0001601
  • Ina Vertommen, Djordje Mitrović, Karel van Laarhoven, Pieter Piens and Maarten Torbeyns: "Optimization of Water Network Topology and Pipe Sizing to Aid Water Utilities in Deciding on a Design Philosophy: A Real Case Study in Belgium"

    Numerical optimization is gradually finding its way into drinking water practice. For successful introduction of optimization into the sector, it is important that researchers and utility experts work together on the problem formulation with the water utility experts. Water utilities heed the solutions provided by optimization techniques only when the underlying approach and performance criteria match their specific goals. In this contribution, we demonstrate the application of numerical optimization on a real-life problem. The Belgian utility De Watergroep is looking to not only reinforce its distribution networks but to also structurally modify the network’s topology to enhance the quality of water delivered in the future. To help the utility explore the possibilities of these far-reaching changes in the most flexible way possible, an optimization problem was formulated to optimize topology and pipe sizing simultaneously for the distribution network of a Belgian city. The objective of the problem is to minimize the volume of the looped network and thereby work towards a situation where most of the customers are fed by branched extremities of the network. This objective is constrained by pressure and fire flow requirements and thresholds on the number of customers on the branched sections. The requirements for continuity of supply under failure scenarios are guaranteed by these constraints, as verified in the final solution. The results of the optimization process show that it is possible to design a network which is 18.5% cheaper than the currently existing network. Moreover, it turns out the—previously completely meshed—topology can be restructured so that 67% of the network length is turned into branched clusters, with a meshed superstructure of 33% of the length remaining.

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  • Lydia Tsiami, Christos Makropoulos and Dragan Savic: "A review on staged design of water distribution networks"

    Water distribution networks (WDNs) evolve continuously over time. Changes in water

    demands and pipe deterioration require construction upgrades to be performed on the

    network during its entire lifecycle. However, strategically planning WDNs, especially for the

    long term, is a challenging task. This is because parameters that are essential for the

    description of WDNs in the future, such as climate, population and demand transitions, are

    characterized by deep uncertainty. To cope with future uncertainty, and avoid overdesign or

    costly unplanned and reactive interventions, research is moving away from the static design

    of WDNs. Dynamic design approaches, aim to make water networks adaptive to changing

    conditions over long planning horizons. A promising, dynamic design approach is the staged

    design of WDNs, in which the planning horizon is divided into construction phases. This

    approach allows short-term interventions to be made, while simultaneously considering the

    expected long-term network growth outcomes. The aim of this paper is to summarize the

    current state of the art in staged design of water distribution networks. To achieve that, we

    critically examined relevant publications and classified them according to their shared key

    characteristics, such as the nature of the design problem (new or existing network design,

    expansion, strengthening, and rehabilitation), problem formulation (objective functions,

    length of planning horizon), optimization method, and uncertainty considerations. In the

    process, we discuss the latest findings in the literature, highlight the major contributions of

    staged design on water distribution networks, and suggest future research directions.

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  • Dragan Savić, Barbara Hammer, Phoebe Koundouri, Marios Polycarpou: " Long term transitioning of water distribution systems"

    The percentage of the world population living in urban settlements is expected to increase to

    70% of 9.7 billion by 2050. Historically, as cities grew, the development of new water

    infrastructures followed as needed. However, these developments had less to do with real

    planning than with reacting to crisis situations and urgent needs, due to the inability of urban

    water planners to consider long-term, deeply uncertain and ambiguous factors affecting urban

    development and water demand. The “Smart Water Futures: Designing the Next Generation of

    Urban Drinking Water Systems” or “Water-Futures” project, which was funded by the

    European Research Council (ERC), aims to develop a new theoretical framework for the

    allocation and development decisions on drinking water infrastructure systems so that they

    are: (i) socially equitable, (ii) economically efficient, and (iii) environmentally resilient, as

    advocated by the UN Agenda 2030, Sustainable Development Goals. The ERC Synergy grant

    project tackles the “wicked problem” of transitioning water distribution systems in a holistic

    manner, involving civil engineering, control engineering, machine learning, decision theory

    and environmental economics expertise. Developing a theoretical foundation for designing

    smart water systems that can deliver optimally robust and resilient decisions for short/long-

    term planning is one of the biggest challenges that future cities will be facing. This paper

    presents an overview of related past research on this topic, the knowledge gaps in terms of

    investigating the problem in a holistic manner, and the key early outcomes of the project.

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  • Vaquet V., Artelt A., Brinkrolf J. and Hammer B., "Taking Care of Our Drinking Water: Dealing with Sensor Faults in Water Distribution Networks"

    Vaquet V., Artelt A., Brinkrolf J. and Hammer B., "Taking Care of Our Drinking Water: Dealing with Sensor Faults in Water Distribution Networks", ICANN 2022

    The water supply is part of the critical infrastructure as the accessibility of clean drinking water is essential to ensure the health of the people. To guarantee the availability of fresh water, efficient and reliable water distribution networks are crucial. Monitoring these systems is necessary to avoid deterioration in water quality, deal with leakages and prevent cyber-physical attacks. While the installation of a growing amount of sensors is increasing the possibilities to monitor the system, considering the control of the senors becomes another challenge as sensor faults negatively influence the reliability of systems dealing with leakages and monitoring water quality. In this work, we aim to overcome the negative implications induced by sensor faults by using a sensor fault monitoring system based on three steps. First, established residual based fault detection is applied. In a second step, we extend this method to a fault isolation technique and finally propose fault accommodation by standard imputation techniques and different types of virtual sensors.

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  • Jakob J., Artelt A., Hasenjäger M. and Hammer B., "SAM-kNN Regressor for Online Learning in Water Distribution Networks"

    Jakob J., Artelt A., Hasenjäger M. and Hammer B., "SAM-kNN Regressor for Online Learning in Water Distribution Networks", ICANN 2022

    Water distribution networks are a key component of modern infrastructure for housing and industry. They transport and distribute water via widely branched networks from sources to consumers. In order to guarantee a working network at all times, the water supply company continuously monitors the network and takes actions when necessary – e.g. reacting to leakages, sensor faults and drops in water quality. Since real world networks are too large and complex to be monitored by a human, algorithmic monitoring systems have been developed. A popular type of such systems are residual based anomaly detection systems that can detect events such as leakages and sensor faults. For a continuous high quality monitoring, it is necessary for these systems to adapt to changed demands and presence of various anomalies.

    In this work, we propose an adaption of the incremental SAM-kNN classifier for regression to build a residual based anomaly detection system for water distribution networks that is able to adapt to any kind of change.

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  • Artelt A., Vrachimis S., Eliades D., Polycarpou M. and Hammer B., "One Explanation to Rule them All -- Ensemble Consistent Explanations"

    Artelt A., Vrachimis S., Eliades D., Polycarpou M. and Hammer B., "One Explanation to Rule them All -- Ensemble Consistent Explanations", XAI workshop at IJCAI 2022

    Transparency is a major requirement of modern AI based decision making systems deployed in real world. A popular approach for achieving transparency is by means of explanations. A wide variety of different explanations have been proposed for single decision making systems. In practice it is often the case to have a set (i.e. ensemble) of decisions that are used instead of a single decision only, in particular in complex systems. Unfortunately, explanation methods for single decision making systems are not easily applicable to ensembles -- i.e. they would yield an ensemble of individual explanations which are not necessarily consistent, hence less useful and more difficult to understand than a single consistent explanation of all observed phenomena. We propose a novel concept for consistently explaining an ensemble of decisions locally with a single explanation -- we introduce a formal concept, as well as a specific implementation using counterfactual explanations.

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  • Pittis N., Koundouri P., Samartzis P., Englezos N. and Papandreou A., "Ambiguity aversion, modern Bayesianism and small worlds"

    Pittis N., Koundouri P., Samartzis P., Englezos N. and Papandreou A., "Ambiguity aversion, modern Bayesianism and small worlds" [version 1; peer review: 2 approved], Open Research Europe 2021, 1:13

    The central question of this paper is whether a rational agent under uncertainty can exhibit ambiguity aversion (AA). The answer to this question depends on the way the agent forms her probabilistic beliefs: classical Bayesianism (CB) vs modern Bayesianism (MB). We revisit Schmeidler's coin-based example and show that a rational MB agent operating in the context of a "small world", cannot exhibit AA. Hence we argue that the motivation of AA based on Schmeidler's coin-based and Ellsberg's classic urn-based examples, is poor, since they correspond to cases of "small worlds". We also argue that MB, not only avoids AA, but also proves to be normatively superior to CB because an MB agent (i) avoids logical inconsistencies akin to the relation between her subjective probability and objective chance, (ii) resolves the problem of "old evidence" and (iii) allows psychological detachment from actual evidence, hence avoiding the problem of "cognitive dissonance". As far as AA is concerned, we claim that it may be thought of as a (potential) property of large worlds, because in such worlds MB is likely to be infeasible.

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  • Alamanos, A.; Koundouri, P.; Papadaki, L.; Pliakou, T.; Toli, E. Water for Tomorrow: A Living Lab on the Creation of the Science-Policy-Stakeholder Interface.

    Alamanos, A.; Koundouri, P.; Papadaki, L.; Pliakou, T.; Toli, E. Water for Tomorrow: A Living Lab on the Creation of the Science-Policy-Stakeholder Interface. Water 2022, 14, 2879.

    The proactive sustainable management of scarce water across vulnerable agricultural areas of South Europe is a timely issue of major importance, especially under the recent challenges affecting complex water systems. The Basin District of Thessaly, Greece’s driest rural region, has a long history of multiple issues of an environmental, planning, economic or administrative nature, as well as a history of conflict. For the first time, the region’s key-stakeholders, including scientists and policymakers, participated in tactical meetings during the 19-month project “Water For Tomorrow”. The goal was to establish a common and holistic understanding of the problems, assess the lessons learned from the failures of the past and co-develop a list of policy recommendations, placing them in the broader context of sustainability. These refer to enhanced and transparent information, data, accountability, cooperation/communication among authorities and stakeholders, capacity building, new technologies and modernization of current practices, reasonable demand and supply management, flexible renewable energy portfolios and circular approaches, among others. This work has significant implications for the integrated water resources management of similar south-European cases, including the Third-Cycle of the River Basin Management Plans and the International Sustainability Agendas.

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  • Stelios Vrachimis, Srimanta Santra, Agathoklis Agathokleous, Pavlos Pavlou, Marios Kyriakou, Michalis Psaras, Demetrios G. Eliades, Marios M. Polycarpou, "WaterSafe: A Water Network Benchmark for Fault Diagnosis Research"

    Currently, in the water distribution systems literature, fault detection methods are typically evaluated on benchmark water networks that do not include real-time experimental data, or on private commercial datasets, which prohibit the reproducibility of the results. Moreover, realistic modeling of faults on hydraulic system components, sensors and actuators is often unavailable. In this work, we provide a framework for the application of fault-diagnosis methodologies on WaterSafe, a water network benchmark for fault diagnosis. The WaterSafe benchmark is a small scale replica of a water transport network constructed using industrial components and devices, while the communications are implemented in a way that resemble a water utility's Supervisory Control and Data Acquisition system. A general problem formulation for fault-diagnosis on water systems is provided, in accordance to the mathematical model of the benchmark. Moreover, we provide a calibrated simulation model including system, sensor and actuator faults, based on observations from the real system. Finally, we provide open access to the datasets generated from the experiments containing the aforementioned faults.

    https://www.sciencedirect.com/science/article/pii/S2405896322005870

The Project

About the Project Concept

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Team

People University of Cyprus (UCY) Bielefeld University Athens Univ. of Economics and Business (AUEB) KWR Water Research Institute (KWR) University of Exeter

This project has received funding from the European Research Council (ERC) under the ERC Synergy Grant Water-Futures (Grant agreement No. 951424).

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