When we handle a great number of items, we need a system to categorize them for easy reference, like we use Cardex for business cards, paper file for documents, albums for photos.

• 处理大批数据时需要一个系统分类以方便使用；就好象我们使用名片盒来装名片；用文件夹来存储文件；用相册来装相片.