简体繁体 English

有损或无损分解

[英]Lossy OR Lossless Decomposition

原文 2016-04-30 13:33:05 8 1 normalization/ functional-dependencies/ database-relations/ database-management/ lossless

Consider the relation R(A,B,C,D,E) with the set of F=(A->C,B->C,C->D,DC->C,CE->A) Suppose the relation has been Decomposed by the relations R1(A,D),R2(A,B),R3(B,E),R4(C,D,E),R5(A,E) 考虑具有集合F =（A-> C，B-> C，C-> D，DC-> C，CE-> A）的关系R（A，B，C，D，E）假设该关系通过关系R1（A，D），R2（A，B），R3（B，E），R4（C，D，E），R5（A，E）分解

Is this decomposition lossy or lossless? 这种分解是有损的还是无损的？

i tried solving this question using the matrix method and i am getting the answer as lossless because i managed to get a row in the 5*5 matrix filled with one variable however the book from which i am solving gives the answer as lossy. 我尝试使用矩阵方法解决这个问题，并且我得到的答案是无损的，因为我设法在5 * 5矩阵中的一行中填充了一个变量，但是我要解决的书给出的答案却是有损的。 which one is the correct answer?? 哪个是正确答案？

1 个解决方案

It is a lossless decomposition for sure. 肯定是无损的分解。 The row corresponding to R ₃ gets filled with one variable. 对应于R ₃的行被一个变量填充。

As an aside , if you have the above decomposition obtained using Bernstein Synthesis then just checking whether any of the decomposed relations consists of all the attributes of the key of the original relation R will ensure that it's a lossless decomposition. 顺便说一句 ，如果您具有使用Bernstein Synthesis获得的上述分解，则只需检查任何分解的关系是否包含原始关系R的键的所有属性，即可确保它是无损分解。 For example, BE is the key for the relation R in the example above. 例如，在上面的示例中， BE是关系R的键。 The decomposed relation R ₃ consists of both the primary attributes B and E and hence this ensures a lossless decomposition. 分解关系R ₃由主要属性B和E组成 ，因此确保了无损分解。