XML constraints preservation in relational schema

XML has become the universal format for the representation and exchange of information over the Internet, but relational database is still the dominant data repository. So it is also useful in information exchange and data integration for preserving the semantics of data originating in relational databases. Although several approaches exist, they are incomplete in the sense that they focus only on a part of constraints and ignore the constraints for XML DTDs. We first analyze both constraints in XML and constraints for XML. We also discuss what makes good XML document, and how to guarantee these constraints. At last we present our methods to preserve these constraints with relational schema. Comparing with other methods, our approach can preserve more XML constraints, reduce nesting and redundant data, and avoid storing bad DTDs