Query Processing in Ontology-Based Peer-To-Peer Systems

The distributed, heterogeneous and unstructured nature of the Web poses a new challenge to query-answering over multiple data sources. In particular, it is no longer realistic to assume that the involved data sources act as if they were a single (virtual) source, modelled as a global schema, as is done in classical data integration approaches. In this paper, we propose an alternative approach where we replace the role of a single virtual data source schema with a peer-to-peer approach relying an limited shared (or: overlapping) vocabularies between peers. Since overlaps between vocabularies of peers will be limited, query processing will have to be approximate. We provide a formal model for such approximate query processing based on limited shared vocabularies between peers, and we show how the quality of the approximation can be adjusted in a gradual manner. The result is a flexible architecture for query-processing in large, distributed and heterogeneous environments, based on a formal foundation. This architecture is suitable for knowledge-sharing in the peer-to-peer-style networks that are expected to be typical of the Semantic Web.