title: BIRT: Specifying XML Datasource file as parameter does not work
body: <p>Using BIRT designer 3.7.1, it's easy enough to define a report for an XML file data source; however, the input file name is written into the .rptdesign file as constant value, initially. Nice for the start, but useless in real life. What I want is start the BIRT ReportEngine via the genReport.bat script, specifying the name of the XML data source file as parameter. That should be trivial, but it is surprisingly difficult...</p>
  
  <p>What I found out is this: Instead of defining the XML data source file as a constant in the report definition you can use params["datasource"].value, which will be replaced by the parameter value at runtime. Also, in BIRT Designer you can define the Report Parameter (datasource) and give it a default value, say "file://d:/sample.xml". </p>
  
  <p>Yet, it doesn't work. This is the result of my Preview attempt in Designer:</p>
  
  <pre><code>Cannot open the connection for the driver: org.eclipse.datatools.enablement.oda.xml.
  org.eclipse.datatools.connectivity.oda.OdaException: The xml source file cannot be found or the URL is malformed.
  </code></pre>
  
  <p>ReportEngine, started with 'genReport.bat -p "datasource=file://d:/sample.xml" xx.rptdesign' says nearly the same.
  Of course, I have made sure that the XML file exists, and tried different spellings of the file URL. So, what's wrong?</p>