U ⊨ Σ; that is, U satisfies Σ.
I → U; that is, there is a homomorphism from I to U.
For every instance J (finite or infinite), if J ⊨ Σ and I → J, then U → J.
In , an instance that satisfies (1) and (2) above is called a model of Σ and I and an instance that satisfies (3) above is called strongly universal.
In summary, the chase is a procedure which – whenever it terminates – yields a strongly-universal model.
The set Σ of constraints is usually a set of tuple-generating dependencies (tgds) and equality-generating dependencies (egds) , or, equivalently, embedded dependencies [5, 10]. However, the chase has been extended to wider classes of constraints and to universality under functions other than homomorphisms [6, 7, 9]. In this case, the...
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