To be effective, it must be simple enough to communicate the required data structure to the end user, yet detailed enough that the database designer can create the physical structure.
为了是数据模型更加有效，它必须足够简单以使最终用户能够沟通必需的数据结构，同时它也要足够详细以使数据库设计人员能够创建物理结构。
With 32-bit memory structure, no matter how big the physical RAM is, the instance, database configurations are limited by the 4gb addressable space.
对于32位内存结构，不管物理ram有多大，实例、数据库配置都受到4gb可寻址空间的限制。
When somebody designed that database, they didn't have tables like this, so they moved from a model of abstract things they wanted to represent into some physical database structure.
最初设计数据库时，并不存在这样的表，因此这些表需要从抽象的模型中得出，表现为某些实际的数据库结构。
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