OVERVIEW OF MAJOR COMPONENTS - Database Design and Development: An Essential Guide for IT Professionals - page 42

Contrast this simplicity with the sophistication required in database software.
Realization of the significance of information as a key corporate asset drove the
evolution to database systems. If information is a significant asset, then it has to be
managed well and safeguarded with utmost care. Database software, therefore, has
to be much more than a mere data access mechanism; it has to perform many other
complex functions. This type of complexity warrants specialized software, and that
specialized software is the set of sophisticated programs collectively known as the
database management system (DBMS). The DBMS enables us to represent the data
structures, relationships, and constraints.
In a later section of this chapter, we will look inside the DBMS and examine the
individual components. At this point, you need to convince yourself of the need for
the specialized set of software called DBMS by reviewing the major functions.
Language Interfaces You must already have guessed the need for two types of
languages in the database environment. For defining data structures, you need a
data definition language (DDL). For performing data access operations of retriev-
ing, updating, and deleting data, you need another type of language. Data manipu-
lation language (DML) serves the requirements of data access.
DBMS provides support for DDL and DML. Each particular DBMS works with
a specific DDL, and using that data definition language you can define the data
structures in the data dictionary. The DBMS interprets the syntax and semantics of
the language and records the data structure definitions in the data dictionary. Again,
each particular DBMS works with a specific DML to enable access to data. The
DBMS translates the DML commands into data access instructions. In later
chapters, we will discuss DDL and DML for relational DBMSs in detail.
Storage Management Storage management involves support for sophisticated
data retrieval and update requests. Among the thousands of customers in your data-
base, you may want to get a list of all customers in the state of Wisconsin, who have
bought for more than $10,000 during the past six months, and who have no past due
balances. The storage management component of the DBMS must provide for
complex data requests.
Specifically, the storage manager performs the following functions:
• Simplifies and facilitates access to data
• Provides interface with the operating system to access data
• Translates the data manipulation language (DML) commands to low-level file
access instructions for storing, retrieving, and updating data
• Works with the structure definitions in the data dictionary to store and find
data
• Manages space allocations on permanent secondary storage
Transaction Management What is a transaction in a database environment?
Assume you are an order entry operator and you are in the process of entering an
order from one of your customers for 100 units of Product A. Usually, the order
entry application program works in the following manner. You enter the customer
number, date, order location, shipping details, and 100 units for Product A. The