On the expressive power of semijoin queries
<|reference_start|>On the expressive power of semijoin queries: The semijoin algebra is the variant of the relational algebra obtained by replacing the join operator by the semijoin operator. We provide an Ehrenfeucht-Fraiss\'{e} 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.<|reference_end|>
@article{leinders2003on,
    title={On the expressive power of semijoin queries},
    author={Dirk Leinders (Limburgs Universitair Centrum, Belgium), Jerzy
  Tyszkiewicz (Warsaw University), Jan Van den Bussche (Limburgs Universitair
  Centrum, Belgium)},
    journal={arXiv preprint arXiv:cs/0308014},
    year={2003},
    archivePrefix={arXiv},
    eprint={cs/0308014},
    primaryClass={cs.DB cs.LO}
}