Navigational and Rule-Based Languages for Graph Databases

An important step in data analysis is the exploration of data. For traditional relational databases one of the most powerful tools for performing such analysis is the relational database and the aggregates and rankings that they can compute: for instance, simple statistics such as the average number of links between two types of entities (relations) are easily computed using a query on a relational database and may already provide valuable information. However, for the exploration of graph data, relational databases may not be most practical and scalable. For instance, a statistic such as the shortest path between two given nodes cannot be computed by a relational database. Surprisingly, however, tools for querying graph and network databases are much less well developed than for relational data, and only recently an increasing number of studies are devoted to graph or network databases. Our position is that the development of such graph databases is important both to make basic graph mining easier and to prepare data for more complex types of analysis. An important component of such databases is the language that is used to enable aggregating queries, such as shortest path queries.In this paper, we propose an extension to a previously proposed query language. This extension allows for querying and analyzing databases by using aggregates and ranking. A notable feature of our language is that it also supports probabilistic graph queries by conceiving of such queries as aggregating queries. We demonstrate its value on a simple data analysis task.

Graph theory, which is a branch of discrete mathematics, has emerged as a powerful tool in various domains, including database management. This abstract investigates the ways in which ideas and methods from graph theory which can be applied to database systems, offering a thorough synopsis of their benefits. Complex interactions within data can be well-modeled by using the basic concepts of graph theory, such as nodes, edges, and relationships. Because of its capacity to represent and query complex relationships, graph databases have become more and more popular in the field of database administration. Graph databases are well-suited for situations such as social networks, recommendation systems, and interconnected data domains because they are excellent at representing and traversing relationships, in contrast to standard relational databases, which are excellent at managing structured data. The abstract delves into the key graph-based data models, such as property graphs, RDF (Resource Description Framework), explaining how they facilitate the representation of diverse relationships. Furthermore, it explores the efficient storage and retrieval mechanisms that leverage graph traversal algorithms to extract valuable insights from interconnected datasets. The document highlights specific use cases where graph theory contributes to database management, including fraud detection, social network analysis, and recommendation systems. Additionally, it discusses the challenges associated with integrating graph databases into existing infrastructures and proposes solutions to address scalability and performance concerns. The abstract also touches upon the advancements in graph database query languages (Cypher) and SPARQL, showcasing their expressive power in querying complex relationships. The inclusion of graph-based indexing and optimization techniques demonstrates how database systems can efficiently handle queries involving large-scale graph data. As graph databases continue to evolve, this abstract concludes by outlining potential future directions in the intersection of graph theory and database management. It emphasizes the importance of ongoing research in developing scalable and efficient solutions for managing interconnected data, ultimately paving the way for more sophisticated and context-aware database systems relationships. Furthermore, it explores the efficient storage and retrieval mechanisms that leverage graph traversal algorithms to extract valuable insights from interconnected datasets.

Query languages are the foundations of database teaching and education practices. The broad adoption of graph databases contrasts with the limited research into how they are taught. Contrary to relational databases, graph databases allow navigational queries with higher expressivity and lack an a priori schema. In this paper, we design a multi-step exploratory user study investigating these peculiarities and how they impact the student’s learning process. Focusing on the widely used Cypher graph query language, we studied a new taxonomy for classifying the errors around graph queries and conducted an in-depth analysis. Our investigation highlights several learning barriers, including misunderstanding the semantics of language constructs, the confusion between data and schema, and the pattern-matching mechanism. We expect the lessons learned and the derived best teaching practices to have an impact on database education and to influence future generations of students, researchers, and practitioners working on graph database technologies.

In developing NoSQL databases, a major motivation is to achieve better efficient query performance compared with relational databases. The graph database is a NoSQL paradigm where navigation is based on links instead of joining tables. Links can be implemented as pointers, and following a pointer is a constant time operation, whereas joining tables is more complicated and slower, even in the presence of foreign keys. Therefore, link-based navigation has been seen as a more efficient query approach than using join operations on tables. Existing studies strongly support this assumption. However, query complexity has received less attention. For example, in enterprise information systems, queries are usually complex so data need to be collected from several tables or by traversing paths of graph nodes of different types. In the present study, we compared the query performance of a graph-based database system (Neo4j) and relational database systems (MySQL and MariaDB). The effect of different efficiency issues (e.g., indexing and optimization) were included in the comparison in order to investigate the most efficient solutions for different query types. The outcome is that although Neo4j is more efficient for simple queries, MariaDB is essentially more efficient when the complexity of queries increases. The study also highlighted how dramatically the efficiency of relational database has grown during the last decade.

Graph Database Systems (GDBs) support efficiently storing and retrieving graph data, and have become a critical component in many important applications. Many widely-used GDBs utilize the Gremlin query language to create, modify, and retrieve data in graph databases, in which developers can assemble a sequence of Gremlin APIs to perform a complex query. However, incorrect implementations and optimizations of GDBs can introduce logic bugs, which can cause Gremlin queries to return incorrect query results, e.g., omitting vertices in a graph database. In this paper, we propose Query Di sassembling (QuDi), an effective testing technique to automatically detect logic bugs in Gremlin-based GDBs. Given a Gremlin query Q, QuDi disassembles Q into a sequence of atomic graph traversals TList, which shares the equivalent execution semantics with Q. If the execution results of Q and TList are different, a logic bug is revealed in the target GDB. We evaluate QuDi on six popular GDBs, and have found 25 logic bugs in these GDBs, 10 of which have been confirmed as previously-unknown bugs by GDB developers.

The Next Generation Linkage Management System (NGLMS) was designed around keeping all data in a graph database. However, this constraint, while easily achievable for greenfield projects and/or new data linkage units, may not be easily met where legacy data exists.
 Objectives and ApproachThe NGLMS was extended to encompassed system where data was held partially or even completely in a relational database. By grouping the data managed by the NGLMS into system metadata, record link data and record data and allowing system metadata and record data to be stored separately and independently in either a relational or a graph database, the NGLMS allows hybrid installations of mixed graph and relational data and, with some loss of functionality, purely relational installations.
 ResultsThe functionality of the NGLMS was expanded to allow review of existing legacy data stored in a relational database system. Through minor changes to the server used by the NGLMS Clerical Review tool (NGLMS-CR) the review tools was able to present the same interface and allow the same integration as project stored completely within the graph database.
 Hybrid projects where link information was stored in a graph could be accommodated with no loss of functionality.Relational-only projects allowed clerical review of identified clusters in a manner identical to the graph-only NGLMS but involved some curtailment of the advanced clustering, time-slicing, compositional and concurrent functionality of the NGLMS due to the loss of the functionality provided by a graph database. They do provide an upgrade pathway to hybrid projects and then graph-only projects.
 Conclusion / ImplicationsAllowing the NGLMS to be configured as a hybrid system enables a gradual adoption of the NGLMS toolset and software.
 
 purely relational data still allows the use of the NGLMS-CR with customisable workpools and workflows
 a hybrid relational/graph system where record data is still kept in a relational store but cluster and linkage information is kept in the graph store allows the use of legacy data without major disruption and provides a pathway to full adoption

Schema mappings establish a correspondence between data stored in two databases, called source and target respectively. Query processing under schema mappings has been investigated extensively in the two cases where each target atom is mapped to a query over the source (called GAV, global-as-view), and where each source atom is mapped to a query over the target (called LAV, local-as-view). The general case, called GLAV, in which queries over the source are mapped to queries over the target, has attracted a lot of attention recently, especially for data exchange. However, query processing for GLAV mappings has been considered only for the basic service of query answering, and mainly in the context of conjunctive queries (CQs) in relational databases. In this paper we study query processing for GLAV mappings in a wider sense, considering not only query answering, but also query rewriting, perfectness (the property of a rewriting to compute exactly the certain answers), and query containment relative to a mapping. We deal both with the relational case, and with graph databases, where the basic querying mechanism is that of regular path queries. Query answering in GLAV can be smoothly reduced to a combination of the LAV and GAV cases, and for CQs this reduction can be exploited also for the remaining query processing tasks. In contrast, as we show, GLAV query processing for graph databases is non-trivial and requires new insights and techniques. We obtain upper bounds for answering, rewriting, and perfectness, and show decidability of relative containment.

Today we have to deal with large amounts of data, and for large amounts of interconnected data, graph databases represent an excellent choice. However, some concepts that are used in relational databases are still not supported in graph databases, and this could hinder their wider use. In this article, how relational database concepts have been successfully transferred into graph databases, including integrity constraint support, inheritance, trigger specification, new visual query languages, etc., is demonstrated.

In recent years, graph database systems have become very popular and been deployed mainly in situations where the relationship between data is significant, such as in social networks. Although they do not require a particular schema design, a data model contributes to their consistency. Designing diagrams is an approach to satisfying this demand for a conceptual data model. While researchers and companies have been developing concepts and notations for graph database modeling, their notations focus on their specific implementations. In this article, the authors propose a diagram to address this lack of a generic and comprehensive notation for graph databases modeling, named GRAPHED (Graph Description Diagram for Graph Databases). The authors verified the effectiveness and compatibility of GRAPHED in two case studies: fraud identification, and a biological network model.

Geospatial information has been indispensable for many application fields, including traffic planning, urban planning, and energy management. Geospatial data are mainly stored in relational databases that have been developed over several decades, and most geographic information applications are desktop applications. With the arrival of big data, geospatial information applications are also being modified into, e.g., mobile platforms and Geospatial Web Services, which require changeable data schemas, faster query response times, and more flexible scalability than traditional spatial relational databases currently have. To respond to these new requirements, NoSQL (Not only SQL) databases are now being adopted for geospatial data storage, management, and queries. This paper reviews state-of-the-art geospatial data processing in the 10 most popular NoSQL databases. We summarize the supported geometry objects, main geometry functions, spatial indexes, query languages, and data formats of these 10 NoSQL databases. Moreover, the pros and cons of these NoSQL databases are analyzed in terms of geospatial data processing. A literature review and analysis showed that current document databases may be more suitable for massive geospatial data processing than are other NoSQL databases due to their comprehensive support for geometry objects and data formats and their performance, geospatial functions, index methods, and academic development. However, depending on the application scenarios, graph databases, key-value, and wide column databases have their own advantages.

Graph databases such as neo4j are designed to handle and integrate big data from heterogeneous sources. For flexibility and performance they do not ensure data quality through schemata but leave it to the application level. In this paper, we present a model-driven approach for data integration through graph databases with data sources in relational databases. We model query and update operations in neo4j by triple graph grammars and map these to Gremlin code for execution. In this way we provide a model-based approach to data integration that is both visual and formal while providing the data quality assurances of a schema-based solution.

The importance of big data, one of the most popular and researched topics of today, has been a subject of constant debate. Big data appear in almost every aspect of our lives, such as healthcare, education, shopping, social media, and industry; however, its storage and processing is not very efficient when using traditional methods. Therefore, the aim of this study is to obtain big data using a novel social shopping application that collects data from its users. The application is designed to collect information about people, products, and friendships among people, as well as product relationships, and post creations, and also enables setting up various options to mark products, such as like, buy, have, or help. The data gathered by the system is analyzed using both relational and non-relational databases, and the performance of these databases is then compared using specific queries, to reveal the model which performs better and more efficiently. Three different database models were designed and implemented for the system; a relational database, a document database, and a graph database. As a result of the experiments, there is no single model that is superior to the others as all three databases have their advantages and disadvantages. Therefore, the database selection should be decided based on the application domain.

The article presents a study of the tasks that determine the features of power-loaded networks, and tasks that are solved using graph models for power-loaded networks. The tasks that determine the features of power-loaded networks are communication check, isolation of network components and components, combinatorial tasks on graphs, calculation of flow distribution, graph simplification, optimal impact on the power grid, and determination of power proportions. This article presents the high-level architecture of Neo4j. Neo4j is an open-source graph database management system implemented in Java and is considered the most comprehensive and promising graph database management system. In comparison with modelling a graph database using a relational database management system, this approach allows applying additional optimization in the case of data with a more complex and loaded structure. The article proposes a model of an energy-loaded network, because it is a system of interaction of a large number of loads or consumers, active sources, communication lines. The declarative query language for graph databases Cypher was used for implementation. A graph database of an electrical network with a description of analytical data processing using a mathematical algorithm and software specifics of the work of queries in a multi-relational database environment has been built. When a query is executed for a user-specified network segment, a connectivity component is allocated; then for the selected elements of the network graph, correspondence is made with the elements of the network itself.

Several scientific domains operate on mesh data structures. Computations on meshes share a set of basic abstractions which relates to topological and geometric structure of meshes. Due to the complexity of modeling and querying meshes, the database community has neglected the need for a dedicated mesh database and in particular a high-level mesh query language. Currently, such computations is done by using general-purpose programming languages. Such implementations are tightly coupled with dataset characteristics and thus are less reusable, their maintenance cost is high, and their performance is limited to the memory size. In this paper, we describe syntax and semantic of a high-level query language for scientific meshes (called MQuery) with a level of abstraction that can express queries based on topological and geometric navigations. The language is build on top of a graph-based conceptual mesh data model. We report our results comparing two implementations of the language on top of relational and graph databases with a mesh library.

We propose a query language for a secure interoperable multi-granular provenance framework. The proposed language is independent of the underlying provenance representation and supports different types of provenance queries. We have implemented the query language into our provenance framework which is integrated with CRIS - a real world system for managing scientific data. We have also evaluated our provenance queries based on relational and graph databases.