07-01-2013, 04:53 PM
RDBMS
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INTRODUCTION TO RDBMS
What is DBMS?
Data Models
Relational database management system (RDBMS)
Relational Algebra
Structured query language (SQL)
What Is DBMS?
Data is one of the most important assets of a company. It is very important to make
sure data is stored and maintained accurately and quickly. DBMS (Database
Management System) is a system that is used to store and manage data.
A DBMS is a set of programs that is used to store and manipulation data. Manipulation
of data include the following:
Adding new data, for example adding details of new student.
Deleting unwanted data, for example deleting the details of students who have
completed course.
Changing existing data, for example modifying the fee paid by the student.
A DBMS provides various functions like data security, data integrity, data sharing, data
concurrence, data independence, data recovery etc. However, all database
management systems that are now available in the market like Sybase, Oracle, and
MS-Access do not provide the same set of functions, though all are meant for data
management.
Database managements systems like Oracle, DB2 are more powerful and meant for
bigger companies. Whereas, database management systems like MS-Access are meant
for small companies. So one has to choose the DBMS depending upon the
requirement.
Oracle For Beginners Page: 2
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Features of DBMS
The following are main features offered by DBMS. Apart from these
features different
database management systems may offer different features. For instance, Oracle is
increasing being fine-tuned to be the database for Internet applications. This may not
be found in other database management systems. These are the general features of
database management systems. Each DBMS has its own way of implementing it. A
DBMS may have more features the features discussed here and may also enhance
these features.
Support for large amount of data
Each DBMS is designed to support large amount of data. They provide special ways
and means to store and manipulate large amount of data. Companies are trying to
store more and more amount of data. Some of this data will have to be online
(available every time).
In most of the cases the amount of data that can be stored is not actually constrained
by DBSM and instead constrained by the availability of the hardware. For example,
Oracle can store terabytes of data.
Data sharing, concurrency and locking
DBSM also allows data to be shared by two or more users. The same data can be
accessed by multiple users at the same time – data concurrency. However when same
data is being manipulated at the same time by multiple users certain problems arise.
To avoid these problems, DBMS locks data that is being manipulated to avoid two
users from modifying the same data at the same time.
The locking mechanism is transparent and automatic. Neither we have to inform to
DBMS about locking nor we need to know how and when DBMS is locking the data.
However, as a programmer, if we can know intricacies of locking mechanism used by
DBMS, we will be better programmers.
Data Security
While DBMS allowing data to be shared, it also ensures that data in only accessed by
authorized users. DBMS provides features needed to implement security at the
enterprise level. By default, the data of a user cannot be accessed by other users
unless the owner gives explicit permissions to other users to do so.