在分布式数据库中，（ ）是指用户或应用程序不需要知道逻辑上访问的表具体如何分块存储。
- A.逻辑透明
- B.位置透明
- C.分片透明
- D.复制透明
正确答案及解析
正确答案
解析
本题考查的是分布式数据库相关知识。
分片透明：是指用户不必关系数据是如何分片的，它们对数据的操作在全局关系上进行，即关系如何分片对用户是透明的，因此，当分片改变时应用程序可以不变。分片透明性是最高层次的透明性，如果用户能在全局关系一级操作，则数据如何分布，如何存储等细节自不必关系，其应用程序的编写与集中式数据库相同。
复制透明：用户不用关心数据库在网络中各个节点的复制情况，被复制的数据的更新都由系统自动完成。在分布式数据库系统中，可以把一个场地的数据复制到其他场地存放，应用程序可以使用复制到本地的数据在本地完成分布式操作，避免通过网络传输数据，提高了系统的运行和查询效率。但是对于复制数据的更新操作，就要涉及到对所有复制数据的更新。
位置透明：是指用户不必知道所操作的数据放在何处，即数据分配到哪个或哪些站点存储对用户是透明的。
局部映像透明性（逻辑透明）是最低层次的透明性，该透明性提供数据到局部数据库的映像，即用户不必关系局部DBMS支持哪种数据模型、使用哪种数据操纵语言，数据模型和操纵语言的转换是由系统完成的。因此，局部映像透明性对异构型和同构异质的分布式数据库系统是非常重要的。
本题提到不需要了解具体如何分块存储，如果描述为不需要了解物理存储或存储位置，则为位置透明，而涉及到如果分块存储，应该为分片透明。对于分布式数据库，分片是一种大局性的划分，而物理上的存储位置则更为底层，所以对于如何分块存储，强调更多的是分片而不是物理位置。
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