“…Recently algebraic optimization techniques, as they are standard in relational databases, were used to build XQuery processors where optimizations are stated as algebraic equivalences, e.g. (Naughton et al, 2001;Jagadish et al, 2002;Fiebig et al, 2002;May et al, 2006;Ozcan et al, 2005;Nicola & van der Linden, 2005;Boncz et al, 2006;Liu et al, 2005;Pal et al, 2005). This development is motivated by the ability (1) to apply optimizations known from relational databases and adopt them for XML processing, (2) to prove the correctness of query optimizations based on a formallydefined query representation.…”