Invariance to ordinal transformations in rank-aware databases

Abstract

We study influence of ordinal transformations on results of queries in rank-aware databases which derive their operations with ranked relations from totally ordered structures of scores with infima acting as aggregation functions. We introduce notions of ordinal containment and equivalence of ranked relations and prove that infima-based algebraic operations with ranked relations are invariant to ordinal transformations: Queries applied to original and transformed data yield results which are equivalent in terms of the order given by scores, meaning that top-k results of queries remain the same. We show this important property is preserved in alternative query systems based of relational calculi developed in context of G\"odel logic. We comment on relationship to monotone query evaluation and show that the results can be attained in alternative rank-aware approaches