Virtual Schemas and Bases

We propose the notions of virtual schemas and virtual bases as a coherent way of integrating various features in OODB views. A virtual schema is deened based on some existing (real) schema. A virtual base is obtained when a (real) base is attached to a virtual schema. We study the consequences of this simple assumption. In particular, we observe the diierences between a real schema and a virtual one. We also consider an extension (that we call generic schemas) where it is necessary to specify several real bases to attach data to a virtual schema. We show how the exibility provided by virtual schemas can be used to cope with various dynamic features of database systems.