Answer to Question 1
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Answer to Question 2
In a sequential file organization, the rows in the file are stored in sequence according to a primary key value. To locate a particular row, a program must normally scan the file from the beginning until the desired row is located. A common example of a sequential file is the alphabetic list of persons in the white pages of a phone directory. Sequential files are very fast if you want to process rows sequentially, but they are impractical for random row retrievals. Deleting in an indexed file organization, the rows are stored either sequentially or nonsequentially, and an index is created that allows the application software to locate individual rows. An index is a structure that is used to determine the rows in a file that satisfy some condition. Each entry matches a key value with one or more rows. An index can point to unique rows or to potentially more than one row. An index that allows each entry to point to more than one record is called a secondary key index. One of the most powerful capabilities of indexed file organizations is the ability to create multiple indexes. The main disadvantages to indexed file organizations are the extra space required to store the indexes and the extra time necessary to access and maintain indexes. In a hashed file organization, the location of each row is determined using an algorithm that converts a primary key value into a row address. Although there are several variations of hashed files, in most cases the rows are located nonsequentially as dictated by the hashing algorithm.
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