Using Feature-Based Description Logics to avoid Duplicate Elimination in Object-Relational Query Languages

A sound inference procedure is presented for removing operations that eliminate duplicates in queries formulated in a bag-algebra. The procedure is shown complete for positive queries over finite databases, and operates by appeal to logical consequence problems for feature-based description logics in which a TBox embeds an object-relational schema. For unions of conjunctive queries in which an embedded schema excludes cover constraints, the procedure runs in PTIME, and in EXPTIME otherwise.