Add a concrete method toDate which can transfer text string to date type.
Add new method to handle toDate function.
Change back to pass connection as paramter in getUniqueID, otherwise new connection will cause a error: sequence XML_NODES_ID_SEQ.CURRVAL is not yet defined in this session
Change the prototype of method getUniqeID
changed all mentions of DBAdapter to the new name AbstractDatabase
rename the DB* classes to:AbstractDatabaseOracleAdapterPostgresqlAdapterSqlserverAdapter