Incomplete relational database models based on intervals

Tables are used to represent unknown relations. The three partial tuple types are defined in a table to specify incompleteness relationships among tuples of the same table. For tuples of different tables, the cases where incompleteness is introduced at the relation level, tuple level, or attribute value level are discussed. For each of the models, it is shown that query evaluation is sound in the Imielinski-Lipski sense. None of the models is complete in the Imielinski-Lipski sense. Two of the models in the family are compared with other approaches