Databases Reference
In-Depth Information
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Memory management
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File management
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I/O management
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Network control and communications
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Fault detection and recovery
Database application software can run as server applications, client applica-
tions, or, in many instances, both, running as a distributed application. Com-
ponents dealing with the user interface and data presentation run at the client.
Specialized data processing components run at the server, either on the database
server or on a separate application server. It's common to see database applica-
tion designs that include Web server-based components taking advantage of
Internet technologies. Often, the Internet is used as the communication path
tying the application components together.
Small applications usually consist of just a handful of forms and reports. The
components available in modern DBMSs let you put together a small application
easily and quickly. In addition, support components are provided to help develop
even the most complex of applications within a reasonably short time. The final
mix of what you can do and what you have available depends on both the DBMS
and your application development environment.
2.3.3 DBMS Components
The DBMS deserves special attention. A DBMS is a collection of specialized soft-
ware modules. Database administrators cannot implement, control, and manage
databases without the DBMS. Every request for data must go through the DBMS.
Over the years, the features and functions of DBMSs have broadened, so that
today's DBMSs do not just provide data access. Instead; they contain a powerful
and versatile set of tools. Figure 2-11 shows how the various software modules
making up a DBMS could be grouped as major components.
Database Engine
The kernel or heart of the DBMS is the
database engine,
which coordinates the
tasks performed by all other DBMS components. This helps ensure that every
database operation gets completed correctly and completely. The other compo-
nents depend on the database engine to perform actions for them such as stor-
ing data and other system information, retrieving data, and updating data in the
database.
As an example, consider the database engine's role in processing a query. A
query
refers to an executable statement, such as a statement used to retrieve or
modify data. Suppose you create a query to retrieve production data from the
database. When your users run this query, the DBMS must coordinate the tasks
