The DBMS makes it more convenient to __________ information(检索信息) from the database.
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The data abstraction levels in a DBMS include: __________ level, __________ level and __________ level.
The external level defines the different __________ of the database.
There will be many levels of abstraction between the computer and the ultimate user.
A. 对
B. 错
One user program usually requires all the data in the database.
A. 对
B. 错