Databases Reference
In-Depth Information
The data storage component also relates to the storage of the structure defin-
itions in the data dictionary, the database's metadata.
Metadata
is a term referring
to data about data. It's the data that describes the database and database objects.
The storage format is specific to the database management system software used.
Structure definitions specify database and object schemas. In this context,
schema
refers to the design and structure of database objects. For example, a table's schema
describes, among other items, the columns that make up the table.
Speed is of the essence for the storage devices holding the data dictionary.
This is especially true because, with many database systems, the data dictionary
must be accessed first before the data is accessed.
You may also have removable storage media components, such as a tape
drive or writeable CD or DVD drive, to support database backups and data
archiving. In a well-managed design, databases are backed up regularly. The
backups are used for recovery if and when problems occur and data is lost. You
can run backups to a shared storage location on the network or to local remov-
able media. Also, periodically, you might archive old data to remove it from the
active database for storage in a separate location.
2.3.2 Software Requirements
Collectively, the software component includes the specialized database manage-
ment system (DBMS) (discussed further in Section 2.3.3), operating system soft-
ware, and application programs. The
operating system software,
among the
other tasks that it must perform, acts as the layer between the database man-
agement system and hardware. For example, when a user requests some data
from the database, the database management system processes the request. It
determines what data is requested and where the data is physically located. Then
the DBMS has the operating system software retrieve the data from physical stor-
age. The operating system software, in turn, interacts with physical hardware to
retrieve the data.
The operating system is a required component on any computer. For desktops
PCs, different versions of Microsoft Windows are the most common operating sys-
tem choice. However, acceptance of the Linux operating system is growing steadily,
with many hardware manufacturers offering computers with Linux already installed.
No matter which operating system you run, it serves the same function. It
manages and provides access to hardware resources through software control. To
do this, it includes specialized software components known as device drivers that
let the operating system control the hardware devices installed in and connected
to the computer. It is directly responsible for the following activities:
▲
Hardware management
▲
Process management
