protected function _loadCache($cache_file)
    {
        require $cache_file;
        
        if (!isset($cache_version) || $cache_version != self::CACHE_FILE_VERSION)
        {
          return false;
        }
        
        $this->_source_version = $source_version;
        $this->_browsers = $browsers;
        $this->_userAgents = $userAgents;
        $this->_patterns = $patterns;
        $this->_properties = $properties;

        $this->_cacheLoaded = true;
        
        return true;
    }