A Robust Logical and Computational Characterisation of Peer-to-Peer Database Systems

In this paper we give a robust logical and computational characterisation of peer-to-peer (p2p) database systems. We first define a precise model-theoretic semantics of a p2p system, which allows for local inconsistency handling. We then characterise the general computational properties for the problem of answering queries to such a p2p system. Finally, we devise tight complexity bounds and distributed procedures for the problem of answering queries in few relevant special cases

On Multiple Semantics for Declarative Database Repairs

We study the problem of database repairs through a rule-based framework that we refer to as Delta Rules. Delta Rules are highly expressive and allow specifying complex, cross-relations repair logic associated with Denial Constraints, Causal Rules, and allowing to capture Database Triggers of interest. We show that there are no one-size-fits-all semantics for repairs in this inclusive setting, and we consequently introduce multiple alternative semantics, presenting the case for using each of them. We then study the relationships between the semantics in terms of their output and the complexity of computation. Our results formally establish the tradeoff between the permissiveness of the semantics and its computational complexity. We demonstrate the usefulness of the framework in capturing multiple data repair scenarios for an Academic Search database and the TPC-H databases, showing how using different semantics affects the repair in terms of size and runtime, and examining the relationships between the repairs. We also compare our approach with SQL triggers and a state-of-the-art data repair system

The coDB Robust Peer-to-Peer Database System

In this paper we give an overview of the coDB semantically well-founded P2P DB system. A network of databases, possibly with different schemas, are interconnected by means of GLAV coordination rules, which are inclusions of conjunctive queries, with possibly existential variables in the head; coordination rules may be cyclic. Each node can be queried in its schema for data, which the node can fetch from its neighbours, if a coordination rule is involved. Correctness and termination of query answering is guaranteed also in the case of runtime change in the topology of the network

Query Answering Under Exact View Assumption in Local As View Data Integration System. ⋆

Abstract. In this paper we thoroughly analyze a problem of query answering under Exact View Assumption (EVA) in a data integration system. We propose an algorithm to build a representation of all legal global database instances using conditional tables. Other approaches for query answering as well data and program complexity are analyzed. We found a few tractable cases of answering under EVA using reduction to Constraint Satisfaction Problem.