Ontology-Based Query Processing in a Large-Scale P2P Environment

Due to the characteristics of P2P systems, SQL query processing in these systems is more complex than traditional distributed DBMS. In this context, semantic and structural heterogeneity of local schemas prevent peers to exchange their data in a comprehensive way. Schema heterogeneity could lead to incorrect answers for the localization query. Furthermore, in the optimization phase, the lack of information and the obsolete statistics found in local catalogs make the execution plan suboptimal. In this paper, we propose a new approach to SQL query processing in P2P environments. The main features of proposed approach are: (i) Avoiding any centralized structures of the peers participating in the system, (ii) Integrating a Domain Ontology which ensures a comprehensive data exchange in Chord protocol that guarantees efficient locating of data sources, and (iii) Extending the localization phase to be able to obtain information needed in the optimization phase. This information is more reliable than the statistics found in the local catalogs. We describe our approach in detail with examples.