2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/31743The 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.9 pages, to appear in Information Processing Letters; added results that more clearly delineate the expressive power of SA, added a section that discusses the impact of order on the expressive power of SA, deemphasized the discussion on the relationship with GFDatabasesLogic in Computer ScienceH.2.3; F.4.1text