Date Added: Jul 2010
This paper reviews the coverage of formal Relational Algebra as it applies to distributed, federated databases in varying network topologies. The review shows that a number of Relational Algebra extensions allow distributed relations and federation of heterogeneous database schema. More concrete physical Relational Algebra extensions support access plans for multi-database query processing but lack cost functions dealing with specific network topologies such as scale-free networks, hyper-cubes and Kautz graphs. Statistic gathering techniques are highlighted which allow efficient distribution of database metrics, with the aim of providing optimized query processing.