Summary Pure spectrum‐based fault localization (SBFL) is a well‐studied statistical debugging technique that only takes a set of test cases (some failing and some passing) and their code coverage as input and produces a ranked list of suspicious program elements to help the developer identify the location of a bug that causes a failed test case. Studies show that pure SBFL techniques produce good ranked lists for small programs. However, our previous study based on the iBugs benchmark that uses the A spect J repository shows that, for realistic programs, the accuracy of the ranked list is not suitable for human developers. In this paper, we confirm this based on a combined empirical evaluation with the iBugs and the D efects4 J benchmark. Our experiments show that, on average, at most ∼40 % , ∼80 % , and ∼90 % of the bugs can be localized reliably within the first 10, 100, and 1000 ranked lines, respectively, in the D efects4 J benchmark. To reliably localize 90 % of the bugs with the best performing SBFL metric D ∗ , ∼450 lines have to be inspected by the developer. For human developers, this remains unsuitable, although the results improve compared with the results for the A spect J benchmark. Based on this study, we can clearly see the need to go beyond pure SBFL and take other information, such as information from the bug report or from version history of the code lines, into consideration.

In the past, spectrum-based fault localization (SBFL) techniques have been developed to pinpoint a fault location in a program given a set of failing and successful test executions. Most of the algorithms use similarity coefficients and have only been evaluated on established but small benchmark programs from the Software-artifact Infrastructure Repository (SIR). In this paper, we evaluate the feasibility of applying 33 state-of-the-art SBFL techniques to a large real-world project, namely ASPECTJ. From an initial set of 350 faulty version from the iBugs repository of ASPECTJ we manually classified 88 bugs where SBFL techniques are suitable. Notably, only 11 bugs of these bugs can be found after examining the 1000 most suspicious lines and on average 250 source code files need to be inspected per bug. Based on these results, the study showcases the limitations of current SBFL techniques on a larger program.

Mutual information is a well-established and broadly used concept in information theory. It allows to quantify the mutual dependence between two variables -- an essential task in data analysis. For static data, a broad range of techniques addresses the problem of estimating mutual information. However, the assumption of static data is not applicable for today's dynamic data sources such as data streams: In contrast to static approaches, an online estimator must be able to deal with the evolving, changing, and infinite nature of the stream. Furthermore, some tasks require the estimation to be available online while processing the raw data stream. Our proposed solution Mise (Mutual Information Stream Estimation) allows a user to issue mutual information queries in arbitrary time windows. As a key feature, we introduce a novel sampling scheme, which ensures an equal treatment of queries over multiple time scales, e.g., ranging from milliseconds up to decades. We thoroughly analyze the requirements of such a multiscale sampling scheme, and evaluate the resulting quality of Mise in a broad range of experiments.

There exists a variety of traditional outlier models, which measure the deviation of outliers with respect to the full attribute space. However, these techniques fail to detect outliers that deviate only w.r.t. an attribute subset. To address this problem, recent techniques focus on a selection of subspaces that allow: (1) A clear distinction between clustered objects and outliers; (2) a description of outlier reasons by the selected subspaces. However, depending on the outlier model used, different objects in different subspaces have the highest deviation. It is an open research issue to make subspace selection adaptive to the outlier score of each object and flexible w.r.t. the use of different outlier models.

Current mining algorithms for attributed graphs exploit dependencies between attribute information and edge structure, referred to as homophily. However, techniques fail if this assumption does not hold for the full attribute space. In multivariate spaces, some attributes have high dependency with the graph structure while others do not show any dependency. Hence, it is important to select congruent subspaces (i.e., subsets of the node attributes) showing dependencies with the graph structure. In this work, we propose a method for the statistical selection of such congruent subspaces. More specifically, we define a measure which assesses the degree of congruence between a set of attributes and the entire graph. We use it as the core of a statistical test, which congruent subspaces must pass. To illustrate its applicability to common graph mining tasks and in order to evaluate our selection scheme, we apply it to community outlier detection. Our selection of congruent subspaces enhances outlier detection by measuring outlier ness scores in selected subspaces only. Experiments on attributed graphs show that our approach outperforms traditional full space approaches and gives way to better outlier detection.

In many real world applications data is collected in multi-dimensional spaces, with the knowledge hidden in subspaces (i.e., subsets of the dimensions). It is an open research issue to select meaningful subspaces without any prior knowledge about such hidden patterns. Standard approaches, such as pairwise correlation measures, or statistical approaches based on entropy, do not solve this problem; due to their restrictive pairwise analysis and loss of information in discretization they are bound to miss subspaces with potential clusters and outliers. In this paper, we focus on finding subspaces with strong mutual dependency in the selected dimension set. Chosen subspaces should provide a high discrepancy between clusters and outliers and enhance detection of these patterns. To measure this, we propose a novel contrast score that quantifies mutual correlations in subspaces by considering their cumulative distributions—without having to discretize the data. In our experiments, we show that these high contrast subspaces provide enhanced quality in cluster and outlier detection for both synthetic and real world data.

Outlier mining is a major task in data analysis. Outliers are objects that highly deviate from regular objects in their local neighborhood. Density-based outlier ranking methods score each object based on its degree of deviation. In many applications, these ranking methods degenerate to random listings due to low contrast between outliers and regular objects. Outliers do not show up in the scattered full space, they are hidden in multiple high contrast subspace projections of the data. Measuring the contrast of such subspaces for outlier rankings is an open research challenge. In this work, we propose a novel subspace search method that selects high contrast subspaces for density-based outlier ranking. It is designed as pre-processing step to outlier ranking algorithms. It searches for high contrast subspaces with a significant amount of conditional dependence among the subspace dimensions. With our approach, we propose a first measure for the contrast of subspaces. Thus, we enhance the quality of traditional outlier rankings by computing outlier scores in high contrast projections only. The evaluation on real and synthetic data shows that our approach outperforms traditional dimensionality reduction techniques, naive random projections as well as state-of-the-art subspace search techniques and provides enhanced quality for outlier ranking.