Completeness Information and Its Application to Query Processing
Amihai Motro · 1986
The assumption that a database includes a representation ol every occurrence in the real world environmrnl that it models (the Closed World Asscrtnplio?l) is frequently unrealistic, because it is always made on the database as a whole. This paper introduces a new type of dntab,ase information, called completeness inlormnlion, lo dcscrihe the subsets of the database for which this assumption is correct. With completeness information it is possible to determine whether each ansivcr to a user query is complete, or whether any subsets of it are complete. To users, answers which are accompanied by a statement about their completeness are more mraningful. First, the principles of completeness informn.lion are defined formally, using an abstract data model. Then, specific methods are described for implcmrnting completeness information in the relational modr4. With these methods, each relational algebra query can be n.ccompnnietl wi(.h a.n instantaneous verdict on its coml)letcness (or on the completcncss of some of its subsets).