a Peer Database Management System

Free University of Bozen-Bolzano, Italy

    The coDBz project studies the problem of efficient query processing in a network of databases, possibly with different schemas, interconnected by means of mapping rules at the schema level. In the coDBz system the case of GLAV mapping rules with conjunctive queries is considered, possibly containing existential variables both in the body and in the head. Each node can be queried locally for data, which the node can fetch from its neighbours if a mapping rule is involved. There are no restrictions on the topology of the network, in particular, cyclic networks are allowed. Dynamic networks are supported: if nodes and mapping rules appear or disappear during the computation, the query processing will eventually terminate with a sound and complete result. We have studied and evaluated optimisations of the query processing algorithm based on dynamic exploration and analysis of the topology of the network. The coDBz system employs a robust algorithm polynomial both in the size of the (dynamic) network and in the size of the global data.

Enrico Franconi