Analyzing, Comparing and Debugging Schema Mappings

K1 is an instance such that K1⊆ K and K satisfies σ σ is a tgd ϕ (x)→∃ y ψ (x, y) h is a homomorphism from ϕ (x)∧ ψ (x, y) to K such that h is also a homomorphism from ϕ (x) to K1