The goal of uncertain databases is to manage information on which there is some uncertainty.
Uncertain databases make it possible to explicitly represent and manage uncertainty on the data, usually in a succinct way.
At the basis of uncertain databases is the notion of possible world.
A given uncertain database typically has more than one, and potentially infinitely many, possible worlds.
These have been called[7] Imieliński–Lipski algebras: The following table is a relation of an incomplete database, described in the formalism of NULL values: There are infinitely many possible worlds for this incomplete database, obtained by replacing the "NULL" values with concrete values.