Semantic integrity aspects in distributed data base management systems

The today applications are very requiring for semantic integrity. However few real database systems provide such capabilities. In this paper some aspects of semantic integrity are discussed. The functional structure of an integrity subsystem is defined as composed by four modules: Language for Integrity Constraint Definition, Integrity Constraint Processor, Integrity Checking Strategy Definer, Integrity Constraint Enforcer. Some implementation aspects of an integrity subsystem in Distributed Database Manaeement Systems are discussed. The notion of distributed constraint definition is introduced. This allows to define constraints in terms of relations stored at different sites. Also strategies are discussed to enforce integrity constraints in distributed way.