2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/165970World-set algebra is a variable-free query language for uncertain databases. It constitutes the core of the query language implemented in MayBMS, an uncertain database system. This paper shows that world-set algebra captures exactly second-order logic over finite structures, or equivalently, the polynomial hierarchy. The proofs also imply that world-set algebra is closed under composition, a previously open problem.22 pages, 1 figureDatabasesLogic in Computer ScienceH.2.3text