Interface Capabilities for Query Processing in Peer Mediator Systems

A peer mediator system (PMS) is a decentralized mediator system based on the P2P paradigm, where medi- ators integrate data sources and other mediators through views defined in a multi-mediator query language. In a PMS mediator peers compose views in terms of views in other peers - mediators and sources, or directly pose queries in the multi-mediator query language to some peer. All peers are fully autonomous and there is no central catalog or controller. Each peer in a PMS must provide an interface to its data and meta-data su cient to allow the cooperative processing of queries by the PMS. We analyze the computational capabilities and meta-data that a software system has to export in order to participate as a peer in a PMS. For the analysis we identify and compare six classes of peer interfaces with increasing complexity. For each class we investigate the performance and scal- ability implications that result from the available capabilities and required meta-data. Our results are two-fold: i) we provide guidelines for the design of mediator peers that can make best use of the interfaces provided by the data sources, and ii) we analyze the tradeo s in the design of inter-mediator interfaces so that mediator peers can e ciently cooperate to process queries against other composed mediators. Finally we describe the choices made in a concrete implementation of a PMS.