设计出R树索引文件结构。
二次信息组织方式有搜索引擎方式、指示数据库方式、菜单方式、主题树方式；
The mode of secondary information organization includes search engine, referral database, menu, etc.
每棵树展现了被每个搜索引擎爬过的所有节点。
Each tree in the image visualises which nodes are crawled by each search engine.
每棵树展现了被每个搜索引擎爬过的所有节点。
Each tree in the image visualises which nodes are crawled by each search engine.
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