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                # DBMS 中的傳遞依賴 > 原文: [https://beginnersbook.com/2015/04/transitive-dependency-in-dbms/](https://beginnersbook.com/2015/04/transitive-dependency-in-dbms/) 如果函數依賴性由兩個函數依賴性間接形成,則稱其是傳遞的。例如: `如果以下三個函數依賴項成立,則`X -> Z`是傳遞依賴: * `X -> Y` * `Y !-> X` * `Y -> Z` **注意:**傳遞依賴只能在三個或更多屬性的關系中發生。這種依賴性有助于我們在 3NF(第三范式)中對數據庫進行標準化。 **示例**:讓我們舉一個例子來更好地理解它: | **Book** | **Author** | **Author_age** | | Game of Thrones | George R. R. Martin | 66 | | Harry Potter | J. K. Rowling | 49 | | Dying of the Light | George R. R. Martin | 66 | `{Book} ->{Author}`(如果我們知道這本書,我們知道作者姓名) `{Author} !-> {Book}` `{Author} -> {Author_age}` 因此,根據**傳遞依賴的規則**:`{Book} -> {Author_age}`應該成立,這是有道理的,因為如果我們知道書名,我們就可以知道作者的年齡。
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