XML schemas evolve when there are new requirements for the XML data. Your ability to reflect these changes in the database is highly dependent on the storage.If you use relational tables, you can change the table structure and update the XML views to reflect the new mapping from XML to relational tables. If you use CLOB XMLTypes, your new XML data can be directly inserted because this storage allows you to store XML conforming to different XML schemas. However, for XML Schema–based XMLTypes, evolution of their XML schemas is an expensive process because it requires updating of the object-relational structure of the XMLTypes. In Oracle Database 10g, this type of evolution is limited to either performing export/import of the data or using the CopyEvolution() function in the DBMS_XMLSCHEMA package.
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