We develop the notion of sustained models.
Sustained models coincide with partial stable models.
On the basis of sustained models, we develop a semantics for database integrity. Conventional semantics are two-valued, and hence do not explicitly consider states that neither satisfy nor violate integrity. In a sense, they are biased, by either paying more attention to satisfaction than to violation, or vice-versa, independent of any application. Our semantics is three- valued and not biased.