OVERVIEW OF MAJOR COMPONENTS - Database Design and Development: An Essential Guide for IT Professionals - page 49

from the central computer to remote sites. Communication links with sufficient
capacity and speed are essential to handle all the data movement.
Storage of Data
Without the storing of data on secondary storage devices, there is no database. How
you use secondary storage and how you are able to retrieve data from it affects the
performance of the database environment. The storage component contains all data
related to the environment, even including screen formats and report formats.
Data Repository. The repository includes all the data values that are part of the
database. If your database contains information about customers, orders, invoices,
products, and employees, then you store data values of individual customers, orders,
invoices, products, and employees in secondary storage. Two special features are
important for data repository. The secondary storage must provide for fast access
to data so that data requests may be processed speedily. Modern storage media used
for databases are robust and fast. Secondly, data storage must be fault tolerant. Data
storage mechanisms should ensure that the database operations continue even when
some malfunction affects parts of the storage. RAID technology applied to today's
data storage allows you to store copies of data redundantly so that even if one part
gets corrupted, the database operations continue from the duplicate set of data.
Storage of Structure Definitions. The data storage component also relates to the
storage of the structure definitions in the data dictionary. These definitions are also
stored on physical storage as files and records. Structure definitions specify the com-
position of each data element as well as the mappings between external, concep-
tual, and internal schemas. Again, speed is of the essence for the storage devices
holding the data dictionary. This is more so because the data dictionary has to be
accessed first for every data access.
Operating System Software
As we have seen, the collective software component constitutes the specialized
database management system (DBMS), operating system software, and application
programs. Operating system software, among other things, acts as the layer between
database management system and hardware. When a user requests some data from
the database, the database management system processes the request. From the data
dictionary, it determines what data are requested and where the data are stored in
physical storage. Then DBMS requests the operating system software to fetch the
data from physical storage. The operating system software, in turn, interacts with
physical hardware to retrieve the data.
Review the following functions of the operating system software in the database
environment.
Hardware Management. The operating system manages allocation and control of
hardware resources for processing database requests. When multiple users initiate
their requests for data, the operating system prioritizes and sequences the requests
and allocates CPU and other hardware resources to the several database transac-