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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 Lossless-Join Decomposition ： ウィキペディア英語版 Lossless-Join Decomposition In computer science the concept of a Lossless-Join Decomposition is central in removing redundancy safely from databases while preserving the original data. ==Lossless-join Decomposition== Can also be called Nonadditive. If you decompose a relation $R$ into relations $R\_1$ and $R\_2$ you will guarantee a Lossless-Join if $R\_1$⋈$R\_2$ = $R$. If R is split into R1 and R2, for the decomposition to be lossless then at least one of the two should hold true. Projecting on R1 and R2, and joining back, results in the relation you started with.〔http://stackoverflow.com/questions/5771810/lossless-join-property〕 Let $R$ be a relation schema. Let $F$ be a set of functional dependencies on $R$. Let $R\_1$ and $R\_2$ form a decomposition of $R$. The decomposition is a lossless-join decomposition of R if at least one of the following functional dependencies are in $F$+ (where $F$+ stands for the closure for every attribute or attribute sets in $F$): * $R\_1$ ∩ $R\_2$ → $R\_1$ * $R\_1$ ∩ $R\_2$ → $R\_2$ 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「Lossless-Join Decomposition」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.