@TechReport{	  it:2003-048,
  author	= {Timour Katchaounov and Tore Risch},
  title		= {Interface Capabilities for Query Processing in Peer
		  Mediator Systems},
  institution	= {Department of Information Technology, Uppsala University},
  department	= {Computing Science Division},
  year		= {2003},
  number	= {2003-048},
  month		= sep,
  abstract	= {A peer mediator system (PMS) is a decentralized mediator
		  system based on the P2P paradigm, where mediators 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
		  sufficient 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 scalability implications that result from
		  the available capabilities and required meta-data. Our
		  results are two-fold: \emph{i)} we provide guidelines for
		  the design of mediator peers that can make best use of the
		  interfaces provided by the data sources, and \emph{ii)} we
		  analyze the tradeoffs in the design of inter-mediator
		  interfaces so that mediator peers can efficiently cooperate
		  to process queries against other composed mediators.
		  Finally we describe the choices made in a concrete
		  implementation of a PMS.}
}