Many data analysis and knowledge mining tasks require a basic understanding of the content of a dataset prior to any data access. In this demo, we showcase how data descriptions---a set of compact, readable and insightful formulas of boolean predicates---can be used to guide users in understanding datasets. Finding the best description for a dataset is, unfortunately, both computationally hard and task-specific. This demo shows that not only we can generate descriptions at interactive speed, but also that diverse user needs---from anomaly detection to data exploration---can be accommodated through a user-driven process exploiting dynamic programming in concert with a set of heuristics.

The huge diversity of database technologies in use inside organizations pose today new challenges of data management and integration. Polystores provide a solution to this scenario based on a loosely coupled integration of data sources and the direct access, with the local language, to each storage engine for exploiting its distinctive features. However, given the absence of a global schema, it is hard to know if a query to one system can be satisfied with data stored elsewhere in the polystore. We address this issue by introducing query augmentation, a data manipulation operator for polystores based on the automatic enrichment of the answer to a local query with related data in the rest of the polystore. Augmentation can be used to implement two effective methods for data access in polystores: augmented search and augmented exploration. We show that they provide effective tools for information discovery in polystores that avoid middleware layers, abstract query languages, and shared data models. We also illustrate the design of QUEPA, a system that fully implements our approach in an efficient way. A comprehensive campaign of experiments done with QUEPA shows that our approach is feasible and, unlike other approaches, scales nicely as the polystore grows in the number of stores and size of databases.

Paddling in a data lake is strenuous for a data scientist. Being a loosely-structured collection of raw data with little or no meta-information available, the difficulties of extracting insights from a data lake start from the initial phases of data analysis. Indeed, data preparation, which involves many complex operations (such as source and feature selection, exploratory analysis, data profiling, and data curation), is a long and involved activity for navigating the lake before getting precious insights at the finish line. In this framework, we demonstrate KAYAK, a framework that supports data preparation in a data lake with ad-hoc primitives and allows data scientists to cross the finish line sooner. KAYAK takes into account the tolerance of the user in waiting for the primitives' results and it uses incremental execution strategies to produce informative previews of these results. The framework is based on a wise management of metadata and on features that limit human intervention, thus scaling smoothly when the data lake evolves.

The detection of communities in social networks is a challenging task. A rigorous way to model communities considers maximal cliques, that is, maximal subgraphs in which each pair of nodes is connected by an edge. State-of-the-art strategies for finding maximal cliques in very large networks decompose the network in blocks and then perform a distributed computation. These approaches exhibit a trade-off between efficiency and completeness: decreasing the size of the blocks has been shown to improve efficiency but some cliques may remain undetected since high-degree nodes, also called hubs, may not fit with all their neighborhood into a small block. In this paper, we present a distributed approach that, by suitably handling hub nodes, is able to detect maximal cliques in large networks meeting both completeness and efficiency. The approach relies on a two-level decomposition process. The first level aims at recursively identifying and isolating tractable portions of the network. The second level further decomposes the tractable portions into small blocks. We demonstrate that this process is able to correctly detect all maximal cliques, provided that the sparsity of the network is bounded, as it is the case of real-world social networks. An extensive campaign of experiments confirms the effectiveness, efficiency, and scalability of our solution and shows that, if hub nodes were neglected, significant cliques would be undetected.

One of the most common operations on graph databases is graph pattern matching (e.g., graph isomorphism and more general types of "subgraph pattern matching"). In fact, in some graph query languages every single query is expressed as a graph matching operation. Consequently, there has been a significant amount of research effort in optimizing graph matching operations in graph database systems. As graph databases have scaled in recent years, so too has recent work on scaling graph matching operations. However, the performance of recent proposals for scaling graph pattern matching is limited by the presence of high-degree nodes. These high-degree nodes result in an explosion of intermediate result sizes during query execution, and therefore significant performance bottlenecks. In this paper we present a dedensification technique that losslessly compresses the neighborhood around high-degree nodes. Furthermore, we introduce a query processing technique that enables direct operation of graph query processing operations over the compressed data, without ever having to decompress the data. For pattern matching operations, we show how this technique can be implemented as a layer above existing graph database systems, so that the end-user can benefit from this technique without requiring modifications to the core graph database engine code. Our technique reduces the size of the intermediate result sets during query processing, and thereby improves query performance.

Polystore systems (or simply polystores) have been recently proposed to support a common scenario in which enterprise data are stored in a variety of database technologies relying on different data models and languages. Polystores provide a loosely coupled integration of data sources and support the direct access, with the local language, to each specific storage engine to exploit its distinctive features. Given the absence of a global schema, new challenges for accessing data arise in these environments. In fact, it is usually hard to know in advance if a query to a specific data store can be satisfied with data stored elsewhere in the polystore. QUEPA addresses these issues by introducing augmented search and augmented exploration in a polystore, two access methods based on the automatic enrichment of the result of a query over a storage system with related data in the rest of the polystore. These features do not impact on the applications running on top of the polystore and are compatible with the most common database systems. QUEPA implements in this way a lightweight mechanism for data integration in the polystore and operates in a plug-and-play mode, thus reducing the need for ad-hoc configurations and for middleware layers involving standard APIs, unified query languages or shared data models. In our demonstration audience can experience with the augmentation construct by using the native query languages of the database systems available in the polystore.

The pervasiveness of graphs on the Web is growing; however, the difficulty of managing complex graph structures curbs the development of web-oriented applications that embed network data. The open source project, L evel G raph , aims to overcome the obstacles that web developers face with graph data management. L evel G raph is an easy-to-use graph database layer for web applications. To demonstrate various capabilities of the system, we developed a web-based application that utilizes a graph database of a tourist network in New Delhi. The application allows users to move around the city while L evel G raph executes graph queries on the underlying database. In this demonstration, we show how L evel G raph 's features facilitate development and maintainance of web applications that embed graph data.