Management of Inconsistent Information in Federated Systems

Lack of global consistency control mechanisms, replication of data and uncontrolled transfer of information among the database servers of a federated database system are the main reasons for information inconsistencies in such systems. Database models are largely incapable of handling inconsistent information and the responsibility for managing inconsistencies is transferred to the application or ”middleware” software. The paper introduces an object database model that provides for the flexible representation of a variety of inconsistent information. The model can be considered as a middleware solution to the problem. The model includes the definition of a declarative query language and the evaluation of its formulas in a database with inconsistently specified objects. Furthermore, the problems related to the elimination of redundancies and the nonloss decomposition of the inconsistent information are discussed. The decomposition reduces the complexity of inconsistently specified objects. The decomposed objects can be reconstructed and, therefore, the inconsistent information coming from a number of different sources can be consistently merged. Basic operators for the manipulation of inconsistently specified properties of objects are defined.