private string ConstructBaseURI( string baseURI, string systemId ) {
if ( baseURI == null )
return systemId;
int nCount = baseURI.LastIndexOf('/')+1;
string buf = baseURI;
if ( nCount > 0 && nCount < baseURI.Length )
buf = baseURI.Substring(0, nCount);
else if ( nCount == 0 )
buf = buf + "\\";
return (buf + systemId.Replace('\\', '/'));
}