The second step we discuss is the virtualization of modeled DBs of different types. For virtualization of different types of modeled DB, we describe the schema information of each model using a single common schema. The common schema we will use is an XML Schema. Around it, we will perform virtualization. Fig.5 presents a virtualization method for different database types. To accomplish schema conversion from a different modeled database, we first get the schema information from an RDB to work on. Then we convert it into the correct XML schema for that RDB. Table 1 presents schema conversion correspondences between the two. Because any XML DB is already described in the XML format, we extract the schema information without conversion. For an OODB, we will use the object-
oriented functionality that is available because it is fundamentally an extension of RDB.