Query Evaluation in P2P Systems of Taxonomy-based Sources: Algorithms, Complexity, and Optimizations

TL;DR

This paper investigates algorithms and complexity for query evaluation in P2P systems of taxonomy-based sources, proposing efficient algorithms for centralized and distributed cases, and analyzing their computational properties.

Contribution

It introduces a hypergraph-based algorithm for efficient centralized query evaluation and extends it to distributed P2P systems with correctness proofs.

Findings

Efficient hypergraph-based algorithm for centralized query evaluation

Distributed algorithm with proven correctness for P2P taxonomy networks

Analysis of intractability for more expressive taxonomies

Abstract

In this study, we address the problem of answering queries over a peer-to-peer system of taxonomy-based sources. A taxonomy states subsumption relationships between negation-free DNF formulas on terms and negation-free conjunctions of terms. To the end of laying the foundations of our study, we first consider the centralized case, deriving the complexity of the decision problem and of query evaluation. We conclude by presenting an algorithm that is efficient in data complexity and is based on hypergraphs. More expressive forms of taxonomies are also investigated, which however lead to intractability. We then move to the distributed case, and introduce a logical model of a network of taxonomy-based sources. On such network, a distributed version of the centralized algorithm is then presented, based on a message passing paradigm, and its correctness is proved. We finally discuss optimization issues, and relate our work to the literature.