Unformatted text preview: that has to be processed.
Advantages of Direct Files
Direct files typically have the following advantages:
Given the key, any record can be quickly located and retrieved directly
without the need for sequential search of the file.
2. Transactions need not be sorted and placed in sequence prior to processing.
3. Accumulation of transactions into batches is not required before processing
them. They may t processed as and when generated.
4. It can support interactive online applications that need to provide up-to-theminute information in response to inquiries from users.
5. If required, it is also possible to process direct file records sequentially in a
record key sequence.
Disadvantages of Direct Files
Direct files typically have the following disadvantages: 1. They require relatively expensive hardware and software resources because
they must be stored on direct-access storage device such as a disk.
Due to address generation overhead involved, they are less efficient and
economical than sequential files for use in sequential applications with high
3. Special security measures are often necessary for online direct files that are
simultaneously accessible from multiple online stations.
Indexed Sequential Files
We are all familiar with the concept of an index. For example, the display board
containing the names and room numbers of the various occupants at the entrance
lobby of a large multistoried building is an index that helps us locate a particular
person's room within the building. For instance, to find the room of Dr. Sharma
within the building, we would look up his name in the directory (index) and read
the corresponding floor number and room number. This idea of scanning a
logically sequenced table is preferable to searching door-by-door for the
particular, name. Similarly, if we wished to read the section in this book about
printers, we would not begin on page 1 and read every page until we came across
the topic of interest. Rather, we would find the subject in the...
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This document was uploaded on 04/07/2014.
- Spring '14