Closing Schemas in Object-Relational Databases

Schema closure is a property that guarantees that no schema component has external references, that is, references to components that are not included in the schema. In the context of object-relational databases, schema closure implies that types, tables and views do not have references to components that are not included in the schema. In order to achieve schema closure, in this work two basic approaches known as enlargement closure and reduction closure are proposed. Enlargement closure includes in the schema every referenced component. Reduction closure, on the other hand, is based on the transformation of the components that have external references, eliminating these references to fulfill schema closure. In this work, both closure approaches and the algorithms to carry out the closure in each of them are described. These algorithms generate and incorporate the needed components, whether being types or views, to reach the schema closure making easier therefore the definition of external schemas. Finally, to illustrate the concepts proposed in this work, we explain how to carry out schema closure in SQL:2008.