Organization; General - IBM 1130 User Manual

Section
Subsections
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ORGANIZATION
General
In
a sequentially organized file, records are stored
on the disk in control key sequence, so that records
with successively higher control keys have succes-
sively higher record numbers.
It
is not necessary
(or customary) for the control key to be the same
number as the record number. The only require-
ment is that the control keys be in sequence, and in
sequential (not necessarily consecutive) locations.
Often, to narrow the search for a record in a se-
quential file, an index is consulted for the record
number. This index is a sequential list of the keys
of selected data file records with their correspond-
ing record numbers. An example of a sequentially
organized data file is a telephone directory, in which
people are listed one after the other, in alphabetic
order, the control key being the last name/first
name combination, and the data being the telephone
number.
In a randomly organized file, the records are
generally stored in the sequence of their control
keys. However, a mathematical transformation of
the control key yields the record number. To find
a record in such a file, the record number is com-
puted from the control key by using the same trans-
formation formula. In the random approach no index
tables are required.