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What Are The Difference Between Physical And Logical Data Independence?

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Physical Independence: Therefore, the logical scheme may stay unchanged even though the storage space or type of some data is changed for reasons of optimisation or reorganisation.

Logical Independence: Also the external scheme may stay unchanged for most changes of the logical scheme. This is especially desirable as in this case the application software does not need to be modified or newly translated.
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They are two different data abstract descriptions,and belong to two levels,namely, physical level and logical level.The physical level describes how the data are actually stored and describes complex low-level data structures in details;The logical level is a next-higher level than above,and describes the relationships among data using a simple structures.

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