Description
     The Constructor can take a Pear::DB Data Source Name (DSN) and will then connect
     to the database; or a PEAR::DB object handle, if you already connected the
     database before. Providing sql-strings will not work. 
    
     If you provide only a DSN, you have to add
     a DB_result object, SQL statment or an array later.
    
     The $root parameter is used, if you want to provide another name for your
     root-tag than <root>. If you give an empty string (""), there will be no   
     root element created here, but only when you add a resultset, array or
     SQL Statment.
     And the first tag of this result is used as the root tag.