The ubiquity of data lakes has created fascinating new challenges for data management research. In this tutorial, we review the state-of-the-art in data management for data lakes. We consider how data lakes are introducing new problems including dataset discovery and how they are changing the requirements for classic problems including data extraction, data cleaning, data integration, data versioning, and metadata management.

Repairing erroneous or conflicting data that violate a set of constraints is an important problem in data management. Many automatic or semi-automatic data-repairing algorithms have been proposed in the last few years, each with its own strengths and weaknesses. Bart is an open-source error-generation system conceived to support thorough experimental evaluations of these data-repairing systems. The demo is centered around three main lessons. To start, we discuss how generating errors in data is a complex problem, with several facets. We introduce the important notions of detectability and repairability of an error, that stand at the core of Bart. Then, we show how, by changing the features of errors, it is possible to influence quite significantly the performance of the tools. Finally, we concretely put to work five data-repairing algorithms on dirty data of various kinds generated using Bart, and discuss their performance.

Integration systems are typically evaluated using a few real-world scenarios (e.g., bibliographical or biological datasets) or using synthetic scenarios (e.g., based on star-schemas or other patterns for schemas and constraints). Reusing such evaluations is a cumbersome task because their focus is usually limited to showcasing a specific feature of an approach. This makes it difficult to compare integration solutions, understand their generality, and understand their performance for different application scenarios. Based on this observation, we demonstrate some of the requirements for developing integration benchmarks. We argue that the major abstractions used for integration problems have converged in the last decade which enables the application of robust empirical methods to integration problems (from schema evolution, to data exchange, to answering queries using views and many more). Specifically, we demonstrate that schema mappings are the main abstraction that now drives most integration solutions and show how a metadata generator can be used to create more credible evaluations of the performance and scalability of data integration systems. We will use the demonstration to evangelize for more robust, shared empirical evaluations of data integration systems.

Given the maturity of the data integration field it is surprising that rigorous empirical evaluations of research ideas are so scarce. We identify a major roadblock for empirical work - the lack of comprehensive metadata generators that can be used to create benchmarks for different integration tasks. This makes it difficult to compare integration solutions, understand their generality, and understand their performance. We present iBench, the first metadata generator that can be used to evaluate a wide-range of integration tasks (data exchange, mapping creation, mapping composition, schema evolution, among many others). iBench permits control over the size and characteristics of the metadata it generates (schemas, constraints, and mappings). Our evaluation demonstrates that iBench can efficiently generate very large, complex, yet realistic scenarios with different characteristics. We also present an evaluation of three mapping creation systems using iBench and show that the intricate control that iBench provides over metadata scenarios can reveal new and important empirical insights. iBench is an open-source, extensible tool that we are providing to the community. We believe it will raise the bar for empirical evaluation and comparison of data integration systems.

We study the problem of introducing errors into clean databases for the purpose of benchmarking data-cleaning algorithms. Our goal is to provide users with the highest possible level of control over the error-generation process, and at the same time develop solutions that scale to large databases. We show in the paper that the error-generation problem is surprisingly challenging, and in fact, NP-complete. To provide a scalable solution, we develop a correct and efficient greedy algorithm that sacrifices completeness, but succeeds under very reasonable assumptions. To scale to millions of tuples, the algorithm relies on several non-trivial optimizations, including a new symmetry property of data quality constraints. The trade-off between control and scalability is the main technical contribution of the paper.

The creation of values to represent incomplete information, often referred to as value invention, is central in data exchange. Within schema mappings, Skolem functions have long been used for value invention as they permit a precise representation of missing information. Recent work on a powerful mapping language called second-order tuple generating dependencies (SO tgds), has drawn attention to the fact that the use of arbitrary Skolem functions can have negative computational and programmatic properties in data exchange. In this paper, we present two techniques for understanding when the Skolem functions needed to represent the correct semantics of incomplete information are computationally well-behaved. Specifically, we consider when the Skolem functions in second-order (SO) mappings have a first-order (FO) semantics and are therefore programmatically and computationally more desirable for use in practice. Our first technique, linearization, significantly extends the Nash, Bernstein and Melnik unskolemization algorithm, by understanding when the sets of arguments of the Skolem functions in a mapping are related by set inclusion. We show that such a linear relationship leads to mappings that have FO semantics and are expressible in popular mapping languages including source-to-target tgds and nested tgds. Our second technique uses source semantics, specifically functional dependencies (including keys), to transform SO mappings into equivalent FO mappings. We show that our algorithms are applicable to a strictly larger class of mappings than previous approaches, but more importantly we present an extensive experimental evaluation that quantifies this difference (about 78% improvement) over an extensive schema mapping benchmark and illustrates the applicability of our results on real mappings.

Schema mapping composition is a fundamental operation in schema management and data exchange. The mapping composition problem has been extensively studied for a number of mapping languages, most notably source-to-target tuple-generating dependencies (s-t tgds). An important class of s-t tgds are local-as-view (LAV) tgds. This class of mappings is prevalent in practical data integration and exchange systems, and recent work by ten Cate and Kolaitis shows that such mappings possess desirable structural properties.

We explore the use of a semantic model to support a group of strategic business analysts in their daily work. In particular, we present a set of modeling constructs for representing goals, events and actors that are relevant to the work of analysts. We also describe a qualitative goal analysis procedure which makes it possible to reason about a goal model under different assumptions. The paper also reports on an incremental document classification scheme that can be used to classify relevant documents with respect to the concepts constituting the semantic model.