Big data applications routinely involve diverse datasets: relations flat or nested, complex-structure graphs, documents, poorly structured logs, or even text data. To handle the data, application designers usually rely on several data stores used side-by-side, each capable of handling one or a few data models, and each very efficient for some, but not all, kinds of processing on the data. A current limitation is that applications are written taking into account which part of the data is stored in which store and how. This fails to take advantage of (i) possible redundancy, when the same data may be accessible (with different performance) from distinct data stores; (ii) partial query results (in the style of materialized views) which may be available in the stores. We present ESTOCADA, a novel approach connecting applications to the potentially heterogeneous systems where their input data resides. ESTOCADA can be used in a polystore setting to transparently enable each query to benefit from the best combination of stored data and available processing capabilities. ESTOCADA leverages recent advances in the area of view-based query rewriting under constraints, which we use to describe the various data models and stored data. Our experiments illustrate the significant performance gains achieved by ESTOCADA.

Data management goes through interesting times1, as the number of currently available data management systems (DMSs in short) is probably higher than ever before. This leads to unique opportunities for data-intensive applications, as some systems provide excellent performance on certain data processing operations. Yet, it also raises great challenges, as a system efficient on some tasks may perform poorly or not support other tasks, making it impossible to use a single DMS for a given application. It is thus desirable to use different DMSs side by side in order to take advantage of their best performance, as advocated under terms such as hybrid or poly-stores. We present ESTOCADA, a novel system capable of exploiting side-by-side a practically unbound variety of DMSs, all the while guaranteeing the soundness and completeness of the store, and striving to extract the best performance out of the various DMSs. Our system leverages recent advances in the area of query rewriting under constraints, which we use to capture the various data models and describe the fragments each DMS stores.

RDF is an increasingly popular data model for many practical applications, leading to large volumes of RDF data; efficient RDF data management methods are crucial to allow applications to scale. We propose to demonstrate CliqueSquare, an RDF data management system built on top of a MapReduce-like infrastructure. The main technical novelty of CliqueSquare resides in its logical query optimization algorithm, guaranteed to find a logical plan as flat as possible for a given query, meaning: a plan having the smallest possible number of join operators on top of each other. CliqueSquare's ability to build flat plans allows it to take advantage of a parallel processing framework in order to shorten response times. We demonstrate loading and querying the data, with a particular focus on query optimization, and on the performance benefits of CliqueSquare's flat plans.

As increasing volumes of RDF data are being produced and analyzed, many massively distributed architectures have been proposed for storing and querying this data. These architectures are characterized first, by their RDF partitioning and storage method, and second, by their approach for distributed query optimization, i.e., determining which operations to execute on each node in order to compute the query answers. We present CliqueSquare, a novel optimization approach for evaluating conjunctive RDF queries in a massively parallel environment. We focus on reducing query response time, and thus seek to build flat plans, where the number of joins encountered on a root-to-leaf path in the plan is minimized. We present a family of optimization algorithms, relying on n-ary (star) equality joins to build flat plans, and compare their ability to find the flattest possibles. We have deployed our algorithms in a MapReduce-based RDF platform and demonstrate experimentally the interest of the flat plans built by our best algorithms.

Fact checking and data journalism are currently strong trends. The sheer amount of data at hand makes it difficult even for trained professionals to spot biased, outdated or simply incorrect information. We propose to demonstrate FactMinder, a fact checking and analysis assistance application. SIGMOD attendees will be able to analyze documents using FactMinder and experience how background knowledge and open data repositories help build insightful overviews of current topics.