NoSQL databases do not enforce a fixed and explicit schema, and thus offer a high level of flexibility in designing a database schema. However, how data is structured has a significant impact on the query and update performance. Selecting an appropriate schema depends not only on the application's conceptual data model but also on data characteristics and workload information. The challenge is to determine the most effective data modeling strategy —referencingordenormalization— to improve the overall workload performance. To this end, we provide an automated temporal schema optimization for NoSQL wide-column stores that improves workload performance by making a good trade-off between denormalization and referencing. Using data characteristics and workload information, we propose a two-step transformation from a temporal conceptual model into a model for the Cassandra wide-column store: (i) mapping a temporal UML class model to a schema design graph (SDG) and (ii) mapping the SDG to a Cassandra schema. In the two mappings, we adopt a cost model to optimize schema design via a trade-off between read and write costs. An experimental evaluation demonstrates that our approach generates schemas that lead to significant performance improvements while remaining workload sensitive. For the most expensive cases, our schema reduces the workload latency by up to three orders of magnitude.

Abstract Food waste is a serious problem in modern society. A specific aspect of food waste concerns meat consumption in gastronomy, where typically only prime cuts of meat are used in the kitchen. To facilitate the usage of all parts of animals and thereby reducing food waste, we present Onfoods , a system that recommends alternative meat cuts in recipes and integrates inventory data to help with the creation of menus. Onfoods uses an ontology and a knowledge graph to model recipes, meat cuts and the relationships between the two, similarity measures to find candidates for alternative meat cuts, and inventory data to track the availability of different meat cuts. An intuitive user interface allows the user on one hand to update the knowledge graph and inventory data, and on the other hand to navigate through recipes and choose alternative meat cuts.

Abstract Temporal information plays a crucial role in many database applications, however support for queries on such data is limited. We present an index structure, termed RD-index , to support range-duration queries over interval timestamped relations, which constrain both the range of the tuples’ positions on the timeline and their duration . RD-index is a grid structure in the two-dimensional space, representing the position on the timeline and the duration of timestamps, respectively. Instead of using a regular grid, we consider the data distribution for the construction of the grid in order to ensure that each grid cell contains approximately the same number of intervals. RD-index features provable bounds on the running time of all the operations, allows for a simple implementation, supports very predictable query performance, and can be constructed and queried in parallel using multithreading. We benchmark our solution on a variety of datasets and query workloads, investigating both the query rate and the behavior of the individual queries. The results show that RD-index performs better than the baselines on range-duration queries, for which it is explicitly designed. Furthermore, it outperforms state of the art indexes also on mixed workloads containing queries that constrain either only the duration or the range along with range-duration queries. Finally, the size of the RD-index is in all settings smaller than the competitors, its construction scales with the number of threads, and parallelization helps improving the runtime of expensive moderate and lowly selective queries.

The Variant Call Format (VCF) and its binary counterpart (BCF) are commonly used in bioinformatics for storing gene sequence data. While VCF files provide compact storage, they require specific tools and scripts for querying, thereby missing the rich functionality arsenal of database management systems and their potential for integration in multiomics pipelines. In this paper, we leverage Relational Database Management Systems (RDBMS) to enhance efficiency and flexibility in storing and querying large-scale genetic datasets. We map the VCF file structure to narrow, wide, and array-based data models that are further refined using JSON data structures, resulting in eight data models. Our experimental evaluation shows that RDBMS provide competitive performance in comparison with specialized state-of-the-art tools while making full-fledged database capabilities available for genetic data analysis.

Time series database systems (TSDBs) are prevalent in many applications ranging from monitoring and IoT devices to scientific research. Those systems are specifically designed to efficiently manage data indexed by time. Because of the variety of workloads, the diversity of time series features, and the sophistication of existing TSDBs, there is no clear way to pick the most suitable system. In this demo, we introduce SEER, an automated, configurable, and interactive toolkit to evaluate TSDBs. SEER is based on TSM-Bench, a benchmark tailored for time series database systems used in monitoring applications. It implements an end-to-end pipeline for database benchmarking from data generation and feature contamination to workload evaluation. Users can define their portfolios by configuring and parameterizing custom queries, specifying their frequencies, controlling the type and level of data features, and indicating the type of workloads. Moreover, they can deploy new systems and/or reconfigure the pre-installed ones. SEER would process users' requests and gracefully recommend the best system on a use-case basis.

This paper presents the extended temporal aligner as a temporal primitive, and proposes a set of reduction rules that employ this primitive to convert a temporal join operator to its non-temporal equivalent. The rules cover all types of temporal joins, including inner join, outer joins, and anti-join. Preliminary experimental results demonstrate that the integration of the extended temporal aligner and the reduction rules can efficiently process temporal join queries.

Temporal information plays a crucial role in many database applications, however support for queries on such data is limited. We present an index structure, termed RD-index, to support range-duration queries over interval timestamped relations, which constrain both the range of the tuples’ positions on the timeline and their duration. RD-index is a grid structure in the two-dimensional space, representing the position on the timeline and the duration of timestamps, respectively. Instead of using a regular grid, we consider the data distribution for the construction of the grid in order to ensure that each grid cell contains approximately the same number of intervals. RD-index features provable bounds on the running time of all the operations, allow for a simple implementation, and supports very predictable query performance. We benchmark our solution on a variety of datasets and query workloads, investigating both the query rate and the behavior of the individual queries. The results show that RD-index performs better than the baselines on range-duration queries, for which it is explicitly designed. Furthermore, it outperforms state of the art indexes also on mixed workloads containing queries that constrain either only the duration or the range along with range-duration queries. Finally, the size of the RD-index is in all settings smaller than the competitors.

Time series databases are essential for the large-scale deployment of many critical industrial applications. In infrastructure monitoring, for instance, a database system should be able to process large amounts of sensor data in real-time, execute continuous queries, and handle complex analytical queries such as anomaly detection or forecasting. Several benchmarks have been proposed to evaluate and understand how existing systems and design choices handle specific use cases and workloads. Unfortunately, none of them fully covers the peculiar requirements of monitoring applications. Furthermore, they fall short of providing an automated way to generate representative real-world data and workloads for testing and evaluating these systems. We present TSM-Bench, a benchmark tailored for time series database systems used in monitoring applications. Our key contributions consist of (1) representative queries that meet the requirements that we collected from a water monitoring use case, and (2) a new scalable data generator method based on Generative Adversarial Networks (GAN) and Locality Sensitive Hashing (LSH). We demonstrate, through an extensive set of experiments, how TSM-Bench provides a comprehensive evaluation of the performance of seven leading time series database systems while offering a detailed characterization of their capabilities and trade-offs.

Matchings between objects from two datasets, domains, or ontologies have to be computed in various application scenarios. One often used meta-approach — which we call bipartite data matching — is to leverage domain knowledge for defining costs between the objects that should be matched, and to then use the classical Hungarian algorithm to compute a minimum cost bipartite matching. In this paper, we introduce and study the problem of enumerating K dissimilar minimum cost bipartite matchings. We formalize this problem, prove that it is NP-hard, and present heuristics based on greedy dynamic programming. The presented enumeration techniques are not only interesting in themselves, but also mitigate an often overlooked shortcoming of bipartite data matching, namely, that it is sensitive w. r. t. the storage order of the input data. Extensive experiments show that our enumeration heuristics clearly outperform existing algorithms in terms of dissimilarity of the obtained matchings, that they are effective at rendering bipartite data matching approaches more robust w. r. t. random storage order, and that they significantly improve the upper bounds of state-of-the art algorithms for graph edit distance computation that are based on bipartite data matching.

Abstract Joins are essential and potentially expensive operations in database management systems. When data is associated with time periods, joins commonly include predicates that require pairs of argument tuples to overlap in order to qualify for the result. Our goal is to enable built-in systems support for such joins. In particular, we present an approach where overlap joins are formulated as unions of range joins, which are more general purpose joins compared to overlap joins, i.e., are useful in their own right, and are supported well by B+-trees. The approach is sufficiently flexible that it also supports joins with additional equality predicates, as well as open, closed, and half-open time periods over discrete and continuous domains, thus offering both generality and simplicity, which is important in a system setting. We provide both a stand-alone solution that performs on par with the state-of-the-art and a DBMS embedded solution that is able to exploit standard indexing and clearly outperforms existing DBMS solutions that depend on specialized indexing techniques. We offer both analytical and empirical evaluations of the proposals. The empirical study includes comparisons with pertinent existing proposals and offers detailed insight into the performance characteristics of the proposals.

Stock market events are hard to model. In recent years, one approach that has been receiving increasing attention is to analyze graphs induced by price correlations of different stock companies. By analyzing the structure of such graphs, it is possible to identify critical events, e.g., market crises. To the best of our knowledge, there are no tools available that offer comprehensive support for such analyses. This paper introduces a novel tool that offers in-depth analysis with the ability of fine tuning parameters with an intuitive user interface. With a proposed workflow to handle time series data, the tool becomes versatile and it can analyze correlation graphs of different semantics: minimum spanning tree, graphs with edge thresholds, and evolving graphs. It also provides a rich set of functions that enable users to explore easily, interactively and systematically the correlation graphs starting from a file of raw time series data. With real-world stock data, we demonstrate how straightforward yet effective it is to accomplish various analytical tasks with the proposed tool.

We address the problem of compactly approximating multidimensional range counts with a guaranteed maximum error and propose a novel histogram-based summary structure, termed SliceHist. The key idea is to operate a grid histogram in an approximately rank-transformed space, where the data points are more uniformly distributed and each grid slice contains only a small number of points. Then, the points of each slice are summarised again using the same technique. As each query box partially intersects only few slices and each grid slice has few data points, the summary is able to achieve tight error guarantees. In experiments and through analysis of non-asymptotic formulas we show that SliceHist is not only competitive with existing heuristics in terms of performance, but additionally offers tight error guarantees.

Abstract We develop a family of efficient plane-sweeping interval join algorithms for evaluating a wide range of interval predicates such as Allen’s relationships and parameterized relationships. Our technique is based on a framework, components of which can be flexibly combined in different manners to support the required interval relation. In temporal databases, our algorithms can exploit a well-known and flexible access method, the Timeline Index, thus expanding the set of operations it supports even further. Additionally, employing a compact data structure, the gapless hash map, we utilize the CPU cache efficiently. In an experimental evaluation, we show that our approach is several times faster and scales better than state-of-the-art techniques, while being much better suited for real-time event processing.

Today, most commercial database systems provide some support for the management of temporal data, but the index support for efficiently accessing such data is rather limited. Existing access paths neglect the fact that time intervals are located on the timeline and have a duration, two important pieces of information for querying temporal data.

With the ever increasing amount and complexity of data, visual analysis becomes a fundamental tool to spot correlations and other relationships in data. Most of the previous techniques (e.g., scatter plots or heatmaps) focus on point data, i.e., data with point measures, such as prices or volumes. In this demo paper, we focus on data with interval measures, that is data where measures consist of an interval or range of values, such as price ranges or time intervals. We present a tool, termed HotPeriods, which allows to visualize correlations between two interval measures in the two-dimensional space, where the two measures represent a rectangle. To visualize such data, we first perform a rectangle aggregation. The result of this aggregation is a density matrix, where each cell stores the number of rectangles that cover the corresponding points in space. For the visualization of the density matrix, color-coding is used to represent different density values similar to heatmaps. We illustrate the usefulness of HotPeriods for the analysis of stock market data and tourism data, both of which show interval measures.

Snapshot semantics is widely used for evaluating queries over temporal data: temporal relations are seen as sequences of snapshot relations, and queries are evaluated at each snapshot. In this work, we demonstrate that current approaches for snapshot semantics over interval-timestamped multiset relations are subject to two bugs regarding snapshot aggregation and bag difference. We introduce a novel temporal data model based on K -relations that overcomes these bugs and prove it to correctly encode snapshot semantics. Furthermore, we present an efficient implementation of our model as a database middleware and demonstrate experimentally that our approach is competitive with native implementations.

Time series data is ubiquitous but often incomplete, e.g., due to sensor failures and transmission errors. Since many applications require complete data, missing values must be imputed before further data processing is possible. We propose Top-k Case Matching (TKCM) to impute missing values in streams of time series data. TKCM defines for each time series a set of reference time series and exploits similar historical situations in the reference time series for the imputation. A situation is characterized by the anchor point of a pattern that consists of l consecutive measurements over the reference time series. A missing value in a time series s is derived from the values of s at the anchor points of the k most similar patterns. We show that TKCM imputes missing values consistently if the reference time series pattern-determine time series s, i.e., the pattern of length l at time tn is repeated at least k times in the reference time series and the corresponding values of s at the anchor time points are similar to each other. In contrast to previous work, we support time series that are not linearly correlated but, e.g., phase shifted. TKCM is resilient to consecutively missing values, and the accuracy of the imputed values does not decrease if blocks of values are missing. The results of an exhaustive experimental evaluation using real-world and synthetic data shows that we outperform the state-of-the-art solutions.

In this paper, we present the VISOR tool, which helps the user to explore data and their summary structures by visualizing the relationships between the size k of a data summary and the induced error. Given an ordered dataset, VISOR allows to vary the size k of a data summary and to immediately see the effect on the induced error, by visualizing the error and its dependency on k in an ϵ-graph and Δ-graph, respectively. The user can easily explore different values of k and determine the best value for the summary size. VISOR allows also to compare different summarization methods, such as piecewise constant approximation, piecewise aggregation approximation or V-optimal histograms. We show several demonstration scenarios, including how to determine an appropriate value for the summary size and comparing different summarization techniques.

We propose DigitHist, a histogram summary for selectivity estimation on multi-dimensional data with tight error bounds. By combining multi-dimensional and one-dimensional histograms along regular grids of different resolutions, DigitHist provides an accurate and reliable histogram approach for multi-dimensional data. To achieve a compact summary, we use a sparse representation combined with a novel histogram compression technique that chooses a higher resolution in dense regions and a lower resolution elsewhere. For the construction of DigitHist, we propose a new error measure, termed u -error, which minimizes the width between the guaranteed upper and lower bounds of the selectivity estimate. The construction algorithm performs a single data scan and has linear time complexity. An in-depth experimental evaluation shows that DigitHist delivers superior precision and error bounds than state-of-the-art competitors at a comparable query time.

We develop an algorithm for efficiently joining relations on interval-based attributes with overlap predicates, which, for example, are commonly found in temporal databases. Using a new data structure and a lazy evaluation technique, we are able to achieve impressive performance gains by optimizing memory accesses exploiting features of modern CPU architectures. In an experimental evaluation with real-world datasets our algorithm is able to outperform the state-of-the-art by an order of magnitude.

Many databases contain temporal, or time-referenced, data and use intervals to capture the temporal aspect. While SQL-based database management systems (DBMSs) are capable of supporting the management of interval data, the support they offer can be improved considerably. A range of proposed temporal data models and query languages offer ample evidence to this effect. Natural queries that are very difficult to formulate in SQL are easy to formulate in these temporal query languages. The increased focus on analytics over historical data where queries are generally more complex exacerbates the difficulties and thus the potential benefits of a temporal query language. Commercial DBMSs have recently started to offer limited temporal functionality in a step-by-step manner, focusing on the representation of intervals and neglecting the implementation of the query evaluation engine. This article demonstrates how it is possible to extend the relational database engine to achieve a full-fledged, industrial-strength implementation of sequenced temporal queries, which intuitively are queries that are evaluated at each time point. Our approach reduces temporal queries to nontemporal queries over data with adjusted intervals, and it leaves the processing of nontemporal queries unaffected. Specifically, the approach hinges on three concepts: interval adjustment , timestamp propagation , and attribute scaling . Interval adjustment is enabled by introducing two new relational operators, a temporal normalizer and a temporal aligner, and the latter two concepts are enabled by the replication of timestamp attributes and the use of so-called scaling functions. By providing a set of reduction rules, we can transform any temporal query, expressed in terms of temporal relational operators, to a query expressed in terms of relational operators and the two new operators. We prove that the size of a transformed query is linear in the number of temporal operators in the original query. An integration of the new operators and the transformation rules, along with query optimization rules, into the kernel of PostgreSQL is reported. Empirical studies with the resulting temporal DBMS are covered that offer insights into pertinent design properties of the article's proposal. The new system is available as open-source software.

Each tuple in a valid-time relation includes an interval attribute T that represents the tuple's valid time. The overlap join between two valid-time relations determines all pairs of tuples with overlapping intervals. Although overlap joins are common, existing partitioning and indexing schemes are inefficient if the data includes long-lived tuples or if intervals intersect partition boundaries.

In valid-time databases with interval timestamping each tuple is associated with a time interval over which the recorded fact is true in the modeled reality. The adjustment of these intervals is an essential part of processing interval timestamped data. Some attribute values remain valid if the associated interval changes, whereas others have to be scaled along with the time interval. For example, attributes that record total (cumulative) quantities over time, such as project budgets, total sales or total costs, often must be scaled if the timestamp is adjusted. The goal of this demo is to show how to support the scaling of attribute values in SQL at query time.

In order to process interval timestamped data, the sequenced semantics has been proposed. This paper presents a relational algebra solution that provides native support for the three properties of the sequenced semantics: snapshot reducibility, extended snapshot reducibility, and change preservation. We introduce two temporal primitives, temporal splitter and temporal aligner, and define rules that use these primitives to reduce the operators of a temporal algebra to their nontemporal counterparts. Our solution supports the three properties of the sequenced semantics through interval adjustment and timestamp propagation. We have implemented the temporal primitives and reduction rules in the kernel of PostgreSQL to get native database support for processing interval timestamped data. The support is comprehensive and includes outer joins, antijoins, and aggregations with predicates and functions over the time intervals of argument relations. The implementation and empirical evaluation confirms effectiveness and scalability of our solution that leverages existing database query optimization techniques.