外部层（External Level） 在外部层看到的是使用者观点（User Views）的资料，代表不同使 用者在资料库系统所看见的资料，通常只有部分资料库的资料。
基于8个网页-相关网页
Page Views per user 网页平均访问量 ; 每个访问者的页面浏览数 ; 每个访问者的页面阅读数
user-centered views 用户视角
The user views the server topology.
用户查看服务器拓扑图。
youdao
The user views the PDF version of the Person document.
用户查看该Person文档的PDF版本。
The user views the JPEG image of the Person document as a business card.
用户查看业务卡片形式的Person文档jpeg图像。
If the company deploys the cash from the Alibaba stake sale to successful investments, it can leverage its already large user base to generate higher page views per user.
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In our business model, historically clients have paid for two user-initiated views in order to generate one earned media view.
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We estimate that Facebook currently gets about 415 page views per user per month on average.
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