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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Referential integrity ： ウィキペディア英語版 Referential integrity Referential integrity is a property of data which, when satisfied, requires every value of one attribute (column) of a relation (table) to exist as a value of another attribute in a different (or the same) relation (table). For referential integrity to hold in a relational database, any field in a table that is declared a foreign key can contain either a null value, or only values from a parent table's primary key or a candidate key.〔Coronel et al. (2013). Database Systems 10th ed. Cengage Learning, ISBN 978-1-111-96960-8〕 In other words, when a foreign key value is used it must reference a valid, existing primary key in the parent table. For instance, deleting a record that contains a value referred to by a foreign key in another table would break referential integrity. Some relational database management systems (RDBMS) can enforce referential integrity, normally either by deleting the foreign key rows as well to maintain integrity, or by returning an error and not performing the delete. Which method is used may be determined by a referential integrity constraint defined in a data dictionary. The adjective 'referential' describes the action that a foreign key performs, 'referring' to a link field in another table. In simple terms, 'referential integrity' is a guarantee that the target it 'refers' to will be found. A lack of referential integrity in a database can lead relational databases to return incomplete data, usually with no indication of an error. ==Formalization== An inclusion dependency over two (possibly identical) predicates $R$ and $S$ from a schema is written $R(...,\; A\_n)\; \backslash subseteq\; S(...,\; B\_n)$, where the $A\_i$, $B\_i$ are distinct attributes (column names) of $R$ and $S$. It implies that the tuples of values appearing in columns $A\_1,\; ...,\; A\_n$ for facts of $R$ must also appear as a tuple of values in columns $B\_1,\; ...,\; B\_n$ for some fact of $S$. Logical implication between inclusion dependencies can be axiomatized by inference rules and can be decided by a PSPACE algorithm. The problem can be shown to be PSPACE-complete by reduction from the acceptance problem for a linear bounded automaton.〔 However, logical implication between dependencies that can be inclusion dependencies or functional dependencies is undecidable by reduction from the word problem for monoids.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Referential integrity」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.