(20) Explain how generalization can be implemented in a relational data model.
Ans: Select common properties from different class, create one superclass and add in superclass.
(21) Explain why HDD devices are slower than SSD devices.
Ans: HDD devices are slower than SSD devices as HDD has moving parts which have potential quality drop issue in long term and take longer time to store data due to the disk inside is spinning and mechanical arm need to write data on the disk. While SSD do not have any moving parts. Furthermore, Solid State Drive uses non-volatile memory made from NAND based silicon wafer and data will not be lost on SSD if power lost.
(22) Explain how relational tables are mapped into files.
Logical storage files have data segments, …show more content…
(29) Explain why an index on attribute with very low selectivity may have a negative impact on performance.
Ans: Because primary key has a higher selectivity with automatic index and no need to access on table column.

(30) Explain how hash based index is created.
Ans: Index key use key to find the address of associated record as it is direct computing of keys, no traversal and computation are done in transits memory. Hash index add more bucket then each bucket become smaller and no need to read many data blocks. So hash based index is faster if each bucket is similar.
(31) Explain how it is possible to completely eliminate access to the relational tables when processing the queries.
Ans: Using materialized views as a stored result.

(32) Explain what is "full index scan" and why sometimes it is called as "fast".
Ans: In the full index scan, data are sorted by index keys and reads entire table. So that it helps to eliminate sorting faster to scan.
(33) Explain when many different SELECT statements accessing the same relational table benefits from the same index, support your explanations with an