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Unformatted text preview: sadvantages of Indexed Sequential Files
1. They require relatively expensive hardware and software resources because
they must be stored on a direct-access device such as a disk.
2. They require more storage space than other types of files because the index
file can also become quite large.
When used for direct access online applications, access to records may be
slower than direct files.
File utilities consist of routines, which perform a variety of generalized operations
on data files. Normally, they are quite general in nature in the sense that they can
operate on any data format and even on data files stored on different types of
storage medium. The operations performed by some of the commonly used file
utilities are described below.
Sorting A file sorting utility is used to arrange the records of a file in some defined
sequence. This sequence is determined by the ordering of certain specified fields
(known as keys) within the record. The simplest case of sorting is an ordering of
the records in a file on a single key. For example, the records of an employee file
may be sequenced by ascending order of employee code as shown in Figure 16.4.
A more complex ordering may be produced by introducing a further key in the
sorting process. For example, suppose each record of the employee file also
contains a field for department code to which the employee belongs. Now the
order of sorting may be employee code within department code. This means that
all records for the lowest department code are presented for each employee
belonging to that department in ascending sequence of employee code, then all
records for the next department code, and so on. This is shown in Figure 16.5. Out
of the two keys used in this sorting example, department code is called the primary
key and employee code is called the secondary key because the order oi sorting is
employee code within department code.
The size of keys, the number of keys, and the type of ordering (ascending,
descending), which can be specified as inp...
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This document was uploaded on 04/07/2014.
- Spring '14