This set of RDBMS Multiple Choice Questions & Answers (MCQs) focuses on “Bitmap Indices”.
1. A bitmap is _______
a) An array of bits
b) An index of bits
c) A function mapping all the bits of data
d) None of the mentioned
View Answer
Explanation: A bitmap is simply an array of bits. A bitmap can be used for various purposes such as bitmap indexing.
2. A _________ on the attribute A of relation r consists of one bitmap for each value that A can take
a) Bitmap array
b) Bitmap index
c) Bitmap excess
d) Bitmap
View Answer
Explanation: A bitmap index on the attribute A of relation r consists of one bitmap for each value that A can take. Each bitmap contains as many bits as the number of records in the relation.
3. Intersection of the bitmaps is done by
a) Logical AND
b) Logical OR
c) Logical NOT
d) Logical NOR
View Answer
Explanation: The intersection of the bitmaps is done by the logical AND operation. This is similar to the binary set intersection operation which is done by the logical AND operation.
4. What does an existence bitmap do?
a) It recognizes deleted records
b) It inserts values into empty bitmaps
c) It makes sure that no records are deleted
d) None of the mentioned
View Answer
Explanation: An existence bitmap is used to recognize deleted records and not to prevent deletion of records. It also does not insert any records into empty bitmaps.
5. The complement operation in bitmaps is done by using
a) Logical AND
b) Logical OR
c) Logical NOT
d) Logical NOR
View Answer
Explanation: The complement operation in bitmaps is done by using the logical not operator. This is similar to the binary complement operation.
6. State true or false: Bitmaps can be combined with B+ trees
a) True
b) False
View Answer
Explanation: Bitmaps can be combined with B+ trees for relations where a few attribute values are extremely common.
7. We create an index in SQL using _______ command
a) Create index
b) New index
c) Create new index
d) Develop index
View Answer
Explanation: We create an index in SQL using the create index command. Eg: create index dept_index on instructor(dept_name).
8. We delete and index in SQL using the ________ command
a) Remove index
b) Delete index
c) Drop index
d) None of the mentioned
View Answer
Explanation: We delete and index in SQL using the drop index command. Syntax: drop index
9. State true or false: Intersection operations are extremely slow on bitmaps
a) True
b) False
View Answer
Explanation: Intersection operations are extremely fast on bitmaps making them ideal for supporting queries on multiple attributes.
10. Which of the following operations is used for the union of bitmaps?
a) Logical AND
b) Logical OR
c) Logical NOT
d) Logical NOR
View Answer
Explanation: The logical OR operation is used for the computation of the union of bitmaps. This is similar to the binary set union operation.
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