On the expressive power of semijoin queries
Dirk Leinders, Jerzy Tyszkiewicz, Jan Van den Bussche
Abstract
The semijoin algebra is the variant of the relational algebra obtained by replacing the join operator by the semijoin operator. We provide an Ehrenfeucht-Fraissé game, characterizing the discerning power of the semijoin algebra. This game gives a method for showing that queries are not expressible in the semijoin algebra.
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