Exchange-Repairs: Managing Inconsistency in Data Exchange

In a data exchange setting with target constraints, it is often the case that a given source instance has no solutions. In such cases, the semantics of target queries trivialize. The aim of this paper is to introduce and explore a new framework that gives meaningful semantics in such cases by using the notion of exchange-repairs. Informally, an exchange-repair of a source instance is another source instance that differs minimally from the first, but has a solution. Exchange-repairs give rise to a natural notion of exchange-repair certain answers (XR-certain answers) for target queries. We show that for schema mappings specified by source-to-target GAV dependencies and target equality-generating dependencies (egds), the XR-certain answers of a target conjunctive query can be rewritten as the consistent answers (in the sense of standard database repairs) of a union of conjunctive queries over the source schema with respect to a set of egds over the source schema, making it possible to use a consistent query-answering system to compute XR-certain answers in data exchange. We then examine the general case of schema mappings specified by source-to-target GLAV constraints, a weakly acyclic set of target tgds and a set of target egds. The main result asserts that, for such settings, the XR-certain answers of conjunctive queries can be rewritten as the certain answers of a union of conjunctive queries with respect to the stable models of a disjunctive logic program over a suitable expansion of the source schema.Comment: 29 pages, 13 figures, submitted to the Journal on Data Semantic

Scalability challenges in healthcare blockchain system - a systematic review

Blockchain technology is a private, secure, trustworthy, and transparent information exchange performed in a decentralised manner. In this case, the coordination and validation efforts are simplified as the records are designed to update regularly and there is no difference in the two databases. This review focuses on how the blockchain addresses scalability challenges and provides solutions in the healthcare field through the implementation of blockchain technology. Accordingly, 16 solutions fell under two main areas, namely storage optimization and redesign of blockchain. However, limitations persist, including block size, high volume of data, transactions, number of nodes, and protocol challenges. This review consists of six stages, namely identification of research question, procedures of research, screening of relevant articles, keywording based on the abstract, data extraction, and mapping process. Through Atlas.ti software, the selected keywords were used to analyse through the relevant articles. As a result, 48 codes and 403 quotations were compiled. Manual coding was performed to categorise the quotations. The codes were then mapped onto the network as a mapping process. Notably, 16 solutions fell under two main areas, namely storage optimization and redesign of blockchain. Basically, there are 3 solutions compiled for storage optimization and 13 solutions for the redesign of the blockchain, namely blockchain modelling, read mechanism, write mechanism, and bi-directional network

Relational to RDF Data Exchange in Presence of a Shape Expression Schema

International audienceWe study the relational to RDF data exchange problem, where the target constraints are specified using Shape Expression schema (ShEx). We investigate two fundamental problems: 1) consistency which is checking for a given data exchange setting whether there always exists a solution for any source instance, and 2) constructing a universal solution which is a solution that represents the space of all solutions. We propose to use typed IRI constructors in source-to-target tuple generating dependencies to create the IRIs of the RDF graph from the values in the relational instance, and we translate ShEx into a set of target dependencies. We also identify data exchange settings that are key covered, a property that is decidable and guarantees consistency. Furthermore, we show that this property is a sufficient and necessary condition for the existence of universal solutions for a practical subclass of weakly-recursive ShEx

Algorithms for Core Computation in Data Exchange

We describe the state of the art in the area of core computation for data exchange. Two main approaches are considered: post-processing core computation, applied to a canonical universal solution constructed by chasing a given schema mapping, and direct core computation, where the mapping is first rewritten in order to create core universal solutions by chasing it

Novel information and data exchange within power systems using enhanced blockchain technologies

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonCurrent energy systems are primarily designed for centralized power generation and supplying bulk electricity to users with stable and predictable usage patterns. However, with the increasing penetration of renewable energy sources (RES), future energy systems will require greater flexibility and wider distribution of both demand and supply. Integrating RES on a large scale poses challenges to the hosting capacity of distribution systems. To address these challenges, the digitalization of energy systems through novel Information and Communication Technologies (ICT) infrastructure is essential. The shift from centralized to highly distributed systems necessitates increased coordination and communication efforts. This is because a distributed system is composed of multiple independent entities that need to communicate and collaborate effectively to accomplish a shared objective. Coordination and communication are necessary to ensure that the system is operating efficiently and effectively. Traditional centralized cloud-based data exchange schemes depend on a single trusted third party, this may lead to single-point failure and lack of data privacy and access control. To overcome these issues, a novel approach is proposed for exchanging data within power systems using blockchain technology. This approach enables users to securely exchange data while maintaining ownership. The experiments conducted demonstrate that the proposed approach can handle more users and enables information and data exchange within power systems. Secondly, this thesis proposes an Artificial Neural Network (ANN) based prediction model to optimize the performance of the blockchain-enabled data exchange approach. A use case for exchanging data within the power system is implemented on the proposed platform using various performance metrics. The results of the proposed approach are compared to two other schemes: the baseline scheme and an optimized scheme. The evaluation results indicate that the proposed approach can enhance network performance when compared to the baseline and optimized schemes. In summary, the proposed novel approach to ICT infrastructure for successfully exchanging information and data within power systems entities. The performance of the novel approach is evaluated based on the ability to handle multiple users, scalability, reliability, and security

Data Exchange: Query Answering for Incomplete Data Sources

Data exchange is the problem of transforming data struc-tured under a schema, called the source schema, into data structured under another schema, called the target schema. Existing work on data exchange considers settings where the source instance does not contain incomplete information. In this paper we study semantics and address algorithmic issues for data exchange settings where the source instance may contain incomplete data. We investigate the query answer-ing problem in such data exchange settings. First we give two different meaningful semantics to certain answers: One via the certain answers in the corresponding complete data exchange problems and the other via the set of all solutions of the corresponding complete data exchange problems. We use the chase to compute a universal instance which is ma-terialized over the target schema and is used to compute the certain answers to unions of conjunctive queries. We prove that computing certain answers (under both semantics) for unions of conjunctive queries can be done in polynomial time when the schema mapping contains constraints that consist of a weakly acyclic set of tuple-generating dependencies and equality-generating dependencies. 1