The relational database model was a huge leap forward from the network database model.
關系數據庫模型是網絡數據庫模型的一個巨大飛躍。
Instead of relying on a parent-child or owner-member relationship, the relational model allows any file to be related to any other by means of a common field.
關系模型不依賴于父子關系或所有者-成員關系，而是允許任何文件通過公共字段與任何其他文件相關聯。
Suddenly, the complexity of the design was greatly reduced because changes could be made to the database schema without affecting the system's ability to access data.
突然，設計的復雜性大大降低，因為可以在不影響系統訪問數據能力的情況下對數據庫模式進行更改。
And because access was not by means of paths to and from files, but from a direct relationship between files, new relations between these files could easily be added.
并且由于訪問不是通過文件之間的路徑，而是通過文件之間的直接關系，因此可以輕松地添加這些文件之間的新關系。
In 1970, when E.F. Codd developed the model, it was thought to be impractical.
1970年，當e.f.Codd開發(fā)了這個模型，被認為是不切實際的
The increased ease of use comes at a large performance penalty, and the hardware in those days was not able to implement the model.
增加的易用性帶來了很大的性能損失，并且當時的硬件無法實現該模型。
Since then, of course, hardware has taken huge strides to where today, even the simplest computers can run sophisticated relational database management systems.
當然，從那以后，硬件已經取得了巨大的進步，即使是最簡單的計算機也可以運行復雜的關系數據庫管理系統。
Relational databases go hand-in-hand with the development of SQL.
關系數據庫與SQL的開發(fā)齊頭并進。
The simplicity of SQL - where even a novice can learn to perform basic queries in a short period of time - is a large part of the reason for the popularity of the relational model.
SQL的簡單性 -- 即使是新手也可以在短時間內學習執(zhí)行基本查詢 -- 是關系模型流行的很大一部分原因。

The two tables below relate to each other through the product_code field. Any two tables can relate to each other simply by creating a field they have in common.
下表通過product_code字段相互關聯。任何兩個表都可以通過創(chuàng)建它們共有的字段來相互關聯。
Table 1

Table 2