Abstract:For any query language F, we consider three natural families of boolean queries. Nonemptiness queries are expressed as e = ∅ with e an F expression. Emptiness queries are expressed as e = ∅. Containment queries are expressed as e 1 ⊆ e 2 . We refer to syntactic constructions of boolean queries as modalities. In first order logic, the emptiness, nonemptiness and containment modalities have exactly the same expressive power. For other classes of queries, e.g., expressed in weaker query languages, the modalities … Show more
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