A Framework for Comparing Query Languages in Their Ability to Express Boolean Queries Universiteit Hasselt
We identify three basic modalities for expressing boolean queries using the expressions of a query language: nonemptiness, emptiness, and containment. For the class of first-order queries, these three modalities have exactly the same expressive power. For other classes of queries, e.g., expressed in weaker query languages, the modalities may differ in expressiveness. The expressive power under these different modalities can be compared in ...