Linux Servers

RELATIONAL DATABASE MANAGEMENT SYSTEMS 

DBMS Functions

A DBMS performs several important functions that guarantee the integrity and consistency of the

data in the database. Most of those functions are transparent to end users, and most can be achieved

only through the use of a DBMS. They include data dictionary management, data storage

management, data transformation and presentation, security management, multiuser access control,

backup and recovery management, data integrity management, database access languages and

application programming interfaces and database communication interfaces. Each of these functions

is explained below.

1. Data dictionary management.

The DBMS stores definitions of the data elements and their relationships (metadata) in a data

dictionary. In turn, all programs that access the data in the database work through the DBMS. The

DBMS uses the data dictionary to look up the required data component structures and relationships,

thus relieving you from having to code such complex relationships in each program. Additionally,

any changes made in a database structure are automatically recorded in the data dictionary, thereby

freeing you from having to modify all of the programs that access the changed structure. In other

words, the DBMS provides data abstraction, and it removes structural and data dependence from the

system.

2. Data storage management.

The DBMS creates and manages the complex structures required for data storage, thus relieving you

from the difficult task of defining and programming the physical data characteristics. A modern

DBMS provides storage not only for the data, but also for related data entry forms or screen

definitions, report definitions, data validation rules, procedural code, structures to handle video and

picture formats, and so on. Data storage management is also important for database performance tuning. Performance tuning relates to the activities that make the database perform more efficiently

in terms of storage and access speed.

3. Data transformation and presentation.

The DBMS transforms entered data to conform to required data structures. The DBMS relieves you

of the chore of making a distinction between the logical data format and the physical data format.

That is, the DBMS formats the physically retrieved data to make it conform to the user’s logical

expectations. For example, imagine an enterprise database used by a multinational company. An end

user in England would expect to enter data such as July 11, 2010, as “11/07/2010.” In contrast, the

same date would be entered in the United States as “07/11/2010.” Regardless of the data presentation

format, the DBMS must manage the date in the proper format for each country.

4. Security management.

The DBMS creates a security system that enforces user security and data privacy. Security rules

determine which users can access the database, which data items each user can access, and which

data operations (read, add, delete, or modify) the user can perform. This is especially important in

multiuser database systems.

5. Multiuser access control.

To provide data integrity and data consistency, the DBMS uses sophisticated algorithms to ensure

that multiple users can access the database concurrently without compromising the integrity of the

database.

6. Backup and recovery management.

The DBMS provides backup and data recovery to ensure data safety and integrity. Current DBMS

systems provide special utilities that allow the DBA to perform routine and special backup and

restore procedures. Recovery management deals with the recovery of the database after a failure,

such as a bad sector in the disk or a power failure. Such capability is critical to preserving the

database’s integrity.

7. Data integrity management.

The DBMS promotes and enforces integrity rules, thus minimizing data redundancy and maximizing

data consistency. The data relationships stored in the data dictionary are used to enforce data

integrity. Ensuring data integrity is especially important in transaction-oriented database systems.

8. Database access languages and application programming interfaces.

The DBMS provides data access through a query language. A query language is a nonprocedural

language—one that lets the user specify what must be done without having to specify how it is to be

done. Structured Query Language (SQL) is the de facto query language and data access standard

supported by the majority of DBMS vendors.

9. Database communication interfaces.

Current-generation DBMSs accept end-user requests via multiple, different network environments.

For example, the DBMS might provide access to the database via the Internet through the use of

Web browsers such as Mozilla Firefox or Microsoft Internet Explorer.