Now showing 1 - 10 of 19
No Thumbnail Available
Publication

Explainable production planning under partial observability in high-precision manufacturing

2023-10 , Weichert, Dorina , Kister, Alexander , Volbach, Peter , Houben, Sebastian , Trost, Marcus , Wrobel, Stefan

Conceptually, high-precision manufacturing is a sequence of production and measurement steps, where both kinds of steps require to use non-deterministic models to represent production and measurement tolerances. This paper demonstrates how to effectively represent these manufacturing processes as Partially Observable Markov Decision Processes (POMDP) and derive an offline strategy with state-of-the-art Monte Carlo Tree Search (MCTS) approaches. In doing so, we face two challenges: a continuous observation space and explainability requirements from the side of the process engineers. As a result, we find that a tradeoff between the quantitative performance of the solution and its explainability is required. In a nutshell, the paper elucidates the entire process of explainable production planning: We design and validate a white-box simulation from expert knowledge, examine state-of-the-art POMDP solvers, and discuss our results from both the perspective of machine learning research and as an illustration for high-precision manufacturing practitioners.

No Thumbnail Available
Publication

A generalized Weisfeiler-Lehman graph kernel

2022-04-27 , Schulz, Till Hendrik , Horvath, Tamas , Welke, Pascal , Wrobel, Stefan

After more than one decade, Weisfeiler-Lehman graph kernels are still among the most prevalent graph kernels due to their remarkable predictive performance and time complexity. They are based on a fast iterative partitioning of vertices, originally designed for deciding graph isomorphism with one-sided error. The Weisfeiler-Lehman graph kernels retain this idea and compare such labels with respect to equality. This binary valued comparison is, however, arguably too rigid for defining suitable graph kernels for certain graph classes. To overcome this limitation, we propose a generalization of Weisfeiler-Lehman graph kernels which takes into account a more natural and finer grade of similarity between Weisfeiler-Lehman labels than equality. We show that the proposed similarity can be calculated efficiently by means of the Wasserstein distance between certain vectors representing Weisfeiler-Lehman labels. This and other facts give rise to the natural choice of partitioning the vertices with the Wasserstein k-means algorithm. We empirically demonstrate on the Weisfeiler-Lehman subtree kernel, which is one of the most prominent Weisfeiler-Lehman graph kernels, that our generalization significantly outperforms this and other state-of-the-art graph kernels in terms of predictive performance on datasets which contain structurally more complex graphs beyond the typically considered molecular graphs.

No Thumbnail Available
Publication

Constructing Spaces and Times for Tactical Analysis in Football

2021 , Andrienko, Gennady , Andrienko, Natalia , Anzer, Gabriel , Bauer, Pascal , Budziak, Guido , Fuchs, Georg , Hecker, Dirk , Weber, Hendrik , Wrobel, Stefan

A possible objective in analyzing trajectories of multiple simultaneously moving objects, such as football players during a game, is to extract and understand the general patterns of coordinated movement in different classes of situations as they develop. For achieving this objective, we propose an approach that includes a combination of query techniques for flexible selection of episodes of situation development, a method for dynamic aggregation of data from selected groups of episodes, and a data structure for representing the aggregates that enables their exploration and use in further analysis. The aggregation, which is meant to abstract general movement patterns, involves construction of new time-homomorphic reference systems owing to iterative application of aggregation operators to a sequence of data selections. As similar patterns may occur at different spatial locations, we also propose constructing new spatial reference systems for aligning and matching movements irrespective of their absolute locations. The approach was tested in application to tracking data from two Bundesliga games of the 2018/2019 season. It enabled detection of interesting and meaningful general patterns of team behaviors in three classes of situations defined by football experts. The experts found the approach and the underlying concepts worth implementing in tools for football analysts.

No Thumbnail Available
Publication

Big Data, Big Opportunities

2015 , Wrobel, Stefan , Voß, Hans , Köhler, Joachim , Beyer, Uwe , Auer, Sören

Angetrieben von den technischen Innovationen in der Informatik stehen in allen Bereichen von Wirtschaft, Gesellschaft und Privatleben heute immer mehr Daten zur Verfügung, die potenziell übertragen, gespeichert und analysiert werden könnten, um daraus nützliche Informationen als Grundlage für neue Dienste zu gewinnen. Technische Neuerungen wie die verteilte oder speicherresidente Verarbeitung von Daten haben dazu geführt, dass unsere Analysefähigkeiten so stark gewachsen sind, dass eine neue Klasse von Anwendungen möglich erscheint. Unter dem Schlagwort ,,Big Data"" scheint sich daher zurzeit eine Revolution bei der Nutzung von Daten in allen Bereichen anzukündigen. Der vorliegende Artikel versucht angesichts aktueller Studien zur Nutzung von Big Data-Ansätzen zu beleuchten, inwieweit die großen öffentlichen Erwartungen sich tatsächlich schon im praktischen Ansatz insbesondere in Unternehmen niederschlagen. Er identifiziert darüber hinaus auf Basis allgemeiner und in den Studien zu beobachtender Trends die wichtigsten Herausforderungen, denen sich das Thema Big Data in den nächsten Jahren stellen muss, wenn es die hohen aktuellen Erwartungen auch längerfristig einlösen will.

No Thumbnail Available
Publication

Maximal closed set and half-space separations in finite closure systems

2023-09-21 , Seiffarth, Florian , Horvath, Tamas , Wrobel, Stefan

Several concept learning problems can be regarded as special cases of half-space separation in abstract closure systems over finite ground sets. For the typical scenario that the closure system is given via a closure operator, we show that the half-space separation problem is NP-complete. As a first approach to overcome this negative result, we relax the problem to maximal closed set separation, give a simple generic greedy algorithm solving this problem with a linear number of closure operator calls, and show that this bound is sharp. For a second direction, we consider Kakutani closure systems and prove that they are algorithmically characterized by the greedy algorithm. As a first special case of the general problem setting, we consider Kakutani closure systems over graphs and give a sufficient condition for this kind of closure systems in terms of forbidden graph minors. For a second special case, we then focus on closure systems over finite lattices, give an improved adaptation of the generic greedy algorithm, and present an application concerning subsumption lattices.

No Thumbnail Available
Publication

Visual Analytics for Human-Centered Machine Learning

2022-01-25 , Andrienko, Natalia , Andrienko, Gennady , Adilova, Linara , Wrobel, Stefan

We introduce a new research area in visual analytics (VA) aiming to bridge existing gaps between methods of interactive machine learning (ML) and eXplainable Artificial Intelligence (XAI), on one side, and human minds, on the other side. The gaps are, first, a conceptual mismatch between ML/XAI outputs and human mental models and ways of reasoning, and second, a mismatch between the information quantity and level of detail and human capabilities to perceive and understand. A grand challenge is to adapt ML and XAI to human goals, concepts, values, and ways of thinking. Complementing the current efforts in XAI towards solving this challenge, VA can contribute by exploiting the potential of visualization as an effective way of communicating information to humans and a strong trigger of human abstractive perception and thinking. We propose a cross-disciplinary research framework and formulate research directions for VA.

No Thumbnail Available
Publication

Effective approximation of parametrized closure systems over transactional data streams

2020 , Trabold, Daniel , Horvath, Tamas , Wrobel, Stefan

Strongly closed itemsets, defined by a parameterized closure operator, are a generalization of ordinary closed itemsets. Depending on the strength of closedness, the family of strongly closed itemsets typically forms a tiny subfamily of ordinary closed itemsets that is stable against changes in the input. In this paper we consider the problem of mining strongly closed itemsets from transactional data streams. Utilizing their algebraic and algorithmic properties, we propose an algorithm based on reservoir sampling for approximating this type of itemsets in the landmark streaming setting, prove its correctness, and show empirically that it yields a considerable speed-up over a straightforward naive algorithm without any significant loss in precision and recall. We motivate the problem setting considered by two practical applications. In particular, we first experimentally demonstrate that the above properties, i.e., compactness and stability, make strongly closed itemsets an excellent indicator of certain types of concept drifts in transactional data streams. As a second application we consider computer-aided product configuration, a real-world problem raised by an industrial project. For this problem, which is essentially exact concept identification, we propose a learning algorithm based on a certain type of subset queries formed by strongly closed itemsets and show on real-world datasets that it requires significantly less query evaluations than a naive algorithm based on membership queries.

No Thumbnail Available
Publication

Wasserstein Dropout

2022-09-08 , Sicking, Joachim , Akila, Maram , Pintz, Maximilian Alexander , Wirtz, Tim , Wrobel, Stefan , Fischer, Asja

Despite of its importance for safe machine learning, uncertainty quantification for neural networks is far from being solved. State-of-the-art approaches to estimate neural uncertainties are often hybrid, combining parametric models with explicit or implicit (dropout-based) ensembling. We take another pathway and propose a novel approach to uncertainty quantification for regression tasks, Wasserstein dropout, that is purely non-parametric. Technically, it captures aleatoric uncertainty by means of dropout-based sub-network distributions. This is accomplished by a new objective which minimizes the Wasserstein distance between the label distribution and the model distribution. An extensive empirical analysis shows that Wasserstein dropout outperforms state-of-the-art methods, on vanilla test data as well as under distributional shift in terms of producing more accurate and stable uncertainty estimates.

No Thumbnail Available
Publication

A theoretical model for pattern discovery in visual analytics

2021-01-21 , Andrienko, Natalia , Andrienko, Gennady , Miksch, Silvia , Schumann, Heidrun , Wrobel, Stefan

The word 'pattern' frequently appears in the visualisation and visual analytics literature, but what do we mean when we talk about patterns? We propose a practicable definition of the concept of a pattern in a data distribution as a combination of multiple interrelated elements of two or more data components that can be represented and treated as a unified whole. Our theoretical model describes how patterns are made by relationships existing between data elements. Knowing the types of these relationships, it is possible to predict what kinds of patterns may exist. We demonstrate how our model underpins and refines the established fundamental principles of visualisation. The model also suggests a range of interactive analytical operations that can support visual analytics workflows where patterns, once discovered, are explicitly involved in further data analysis.

No Thumbnail Available
Publication

A review of machine learning for the optimization of production processes

2019 , Weichert, Dorina , Link, Patrick , Stoll, Anke , Rüping, Stefan , Ihlenfeldt, Steffen , Wrobel, Stefan

Due to the advances in the digitalization process of the manufacturing industry and the resulting available data, there is tremendous progress and large interest in integrating machine learning and optimization methods on the shop floor in order to improve production processes. Additionally, a shortage of resources leads to increasing acceptance of new approaches, such as machine learning to save energy, time, and resources, and avoid waste. After describing possible occurring data types in the manufacturing world, this study covers the majority of relevant literature from 2008 to 2018 dealing with machine learning and optimization approaches for product quality or process improvement in the manufacturing industry. The review shows that there is hardly any correlation between the used data, the amount of data, the machine learning algorithms, the used optimizers, and the respective problem from the production. The detailed correlations between these criteria and the recent progress made in this area as well as the issues that are still unsolved are discussed in this paper.