l Sequential file organization. In sequential file
organization, the records are in the same order as they
were written to the file.
l Indexed sequential file organization. In
indexed sequential file organization, the records are
stored in sequence according to a primary key and an
index is created to allow random access of the file. This
type of organization also allows the file to be accessed
sequentially. Indexed sequential is the most commonly
used type of file organization.
l Direct file organization.
In direct file
organization, the records are stored and retrieved using
a relative record number, which gives the position of the
record in the file. This type of organization also allows
the file to be accessed sequentially.
DATABASE MANAGEMENT SYSTEMS
(DBMS)
A database management system (DBMS) is a
software package that provides an integrated source of
data for multiple users, while presenting different views
of that data to different users. It can be characterized as
generalized software that provides a single flexible
facility for accommodating different data files and
operations, while demanding less programming effort
than conventional programming languages. It features
easy access to the data; it facilitates the storage and
maintenance of large volumes of data; and, most
importantly, it provides the capability for sharing the
data resources among different types of users.
Database management systems range from
elementary systems with single record structures,
providing rudimentary report formatting facilities, to
very elaborate systems.
The very elaborate systems
handle several files with hierarchical or relational
structures, perform functions in an online mode, and
have sophisticated query and report writing
capabilities.
DBMSs are being used on a wide variety of
computers in the Navy. Because of this, no one DBMS
by any single manufacturers discussed in this chapter.
Most of the problems with DBMSs in Navy
computer systems are the same as in the civilian
workplace.
A few of these problem areas are noted
below:
. Users do not want to share their data with others
in the database.
. Data representation is inadequate.
. Privacy and safeguarding of proprietary
information are not sufficient.
. Different views of data are needed by technical
and nontechnical DBMS users.
. Data structures are not tailored to individual user
requirements.
The wide use of DBMSs in the Navy indicates that
all or most future operating systems will be oriented
primarily toward DBMS. Slowly, but surely, the DBMS
problems in the preceding list are being eliminated
through better and more sophisticated software,
coupled with advanced training of users on such
software usage.
Take a look at the changes that have been made
from the conventional system file structure to the
database management system structure. As shown in
figure 3-13, a conventional system is many application
Figure 3-13.—A conventional system.
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