Discussion
Which of the following statements are true ?
(i) Logical independence is the capacity to change the conceptual schema without having to change external schema.
(ii) Logical independence is the capacity to change the conceptual schema without having to change internal schema.
(iii) Physical independence is the capacity to change the internal schema without having to change conceptual schema.
(iv) Physical independence is the capacity to change the conceptual schema without having to change external schema
Answer: A
The true statements are (i) and (iii).
In the three-schema architecture, logical data independence is the capacity to change the conceptual schema without having to change the external schemas or application programs (i). Physical data independence is the capacity to change the internal schema without having to change the conceptual schema (iii).
Statement (ii) mixes the two levels: changing the conceptual schema does not normally touch the internal schema. Statement (iv) gives physical independence the definition of logical independence.
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