string Trasforma(string xml_file, string xsl_file)
{
XmlDataDocument doc=new XmlDataDocument();
doc.Load(Request.MapPath(xml_file);
XslTransform xslt=new XslTransform();
xslt.Load(Request.MapPath(xsl_file));
StringBuilder sb=new StringBuilder();
StringWriter sw=new StringWriter(sb);

XmlUrlResolver resolver = new XmlUrlResolver();
xslt.Transform(doc,args,sw,resolver);
sw.Close();
return sb.ToString();
}

string Trasforma(string xml_file, string xsl_file)
{
XslCompiledTransform transform = new XslCompiledTransform();
transform.Load(Request.MapPath(xsl_file));
XmlWriterSettings ws = transform.OutputSettings.Clone();
ws.CheckCharacters = false;
StringBuilder sb = new StringBuilder();
XmlWriter sw = XmlWriter.Create(sb,ws);
transform.Transform(Request.MapPath(xml_file), sw);
return sb.ToString();
}