Key Technologies for Data Management : 21st British National Conference on Databases BNCOD 21 Edinburgh UK July 7 9 2004. Proceedings This book constitutes the refereed proceedings of the 21st British National Conference on Databases BNCOD 2004 held in Edinburgh Scotland UK in July 2004. The 21 revised full papers presented together with an invited paper and the abstract of an invited talk were carefully reviewed and selected from more than 70 submissions. The papers are organized in topical sections on data streams integration and heterogeneity data analytics and manipulation XML interfaces and visualization spatial data and TLAD workshop papers