Dependency Satisfaction in Databases with Incomplete Information

Two of the major problems raised by information incompleteness in databases are how to evaluate queries and how to take data dependencies into account. We give a unified solution of these two intermingled problems for the relational model. Formal criteria for the correctness of the relational algebra and dependency satisfaction are presented. We give a correct redefinition of the complete relational algebra and present a method, called a chase, for enforcing a set of functional and full join dependencies on a relation with null-values of type "value exists, but is presently unknown". This novel chase can also be regarded as a generalization of previously known chase methods. The title of the paper reflects the emphasis of its contribution.