Returns the resource database filename
@returns {null}
function() {
      var m = this.__dbFilename.match(/(^.*)\/([^/]+)$/);
      var resDb;
      if (m && m.length == 3) {
        resDb = m[1] + "/resource-db.json";
      } else {
        resDb = "resource-db.json"; 
      }
      return resDb;
    }