OVERVIEW OF MAJOR COMPONENTS - Database Design and Development: An Essential Guide for IT Professionals - page 43

application program reads the quantity in stock for Product A from the database
and displays 10,000 units. You indicate that you want to complete the order. The
program changes the stock quantity to 9,900 units and updates the database accord-
ingly. As far as the database is concerned, your order entry transaction consists of
a read of the record for Product A containing 10,000 units and an update of the
record to store the revised number of 9,900 units.
In a database environment, many data entry operators like you will be entering
orders simultaneously. Some of these operators may be entering orders for Product
A at the same time you are entering your order. The DBMS must be able to handle
such concurrent transactions and ensure that each transaction leaves the database
in a consistent state. The following components in the DBMS perform transaction
management functions.
Transaction manager. Institutes proper controls for transactions and coordinates
their execution within a database. Enables each transaction to start, perform data-
base accesses, commit the updates permanently in the database, and complete the
execution properly.
Integrity manager. Ensures correctness, accuracy, and validity of the data in the
database through edit and data validity constraints.
Concurrency control manager. Enables concurrent transactions to update the same
database record correctly by using appropriate locking mechanisms. DBMS has
special lock, unlock, and deadlock control modules to assist in concurrency control.
Security Management Protecting the information resource is a major function
of DBMS. All the applications supporting the various business processes in the orga-
nization depend on the data resources in the corporate database. The database acts
as the foundation for running the day-to-day business. The major asset of corporate
information must be safeguarded.
Security management involves preventing unauthorized access to the organiza-
tion's database. Outsiders must be kept away from the database. Several security
methods are available for preventing unauthorized access. The second aspect of
security management deals with providing proper access privileges to those who
should be allowed to use the database. Some parts of the database should be
available for access to selected groups only. For example, corporate payroll data
should be available only to the payroll department and a few other selected
personnel.
Recovery Management What happens to the database when hardware or
software malfunctions happen? Suppose you lose data because of a disk head
crash. Maybe an application program or system software corrupts the data content
and affects the consistency of the database. How do you deal with database
failures? How do you recover lost data or bring the database back to a consistent
state?
Recovery of a database returns it to a consistent state after any kind of failure.
Two modules of the DBMS—log manager and recovery manager—enable recovery
after failures. Log manager saves database updates on another data set, called the