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A introduction to Database Management System
A database (sometimes spelled data base) is also called an electronic database , referring to any
collection of data, or information, that is specially organized for rapid search and retrieval by a computer.
Databases are structured to facilitate the storage, retrieval, modification, and deletion of data in conjunction
with various data-processing operations .Databases can be stored on magnetic disk or tape, optical disk, or
some other secondary storage device.
A database consists of a file or a set of files. The information in these files may be broken down into
records, each of which consists of one or more fields. Fields are the basic units of data storage , and each
field typically contains information pertaining to one aspect or attribute of the entity described by the
database . Using keywords and various sorting commands, users can rapidly search , rearrange, group, and
select the fields in many records to retrieve or create reports on particular aggregate of data.
Complex data relationships and linkages may be found in all but the simplest databases .The system
software package that handles the difficult tasks associated with creating ,accessing, and maintaining
database records is called a database management system(DBMS).The programs in a DBMS package
establish an interface between the database itself and the users of the database.. (These users may be
applications programmers, managers and others with information needs, and various OS programs.)
A DBMS can organize, process, and present selected data elements from the database. This capability
enables decision makers to search, probe, and query database contents in order to extract answers to
nonrecurring and unplanned questions that aren’t available in regular reports. These questions might
initially be vague and/or poorly defined ,but people can “browse” through the database until they have the
needed information. In short, the DBMS will “manage” the stored data items and assemble the needed
items from the common database in response to the queries of those who aren’t programmers.
A database management system (DBMS) is composed of three major parts:(1)a storage subsystem that
stores and retrieves data in files;(2) a modeling and manipulation subsystem that provides the means with
which to organize the data and to add , delete, maintain, and update the data;(3)and an interface between
the DBMS and its users. Several major trends are emerging that enhance the value and usefulness
of database management systems;
Managers: who require more up-to-data information to make effective decision
Customers: who demand increasingly sophisticated information services and more
current information about the status of their orders, invoices, and accounts.
Users: who find that they can develop custom applications with database systems in a fraction of
the time it takes to use traditional programming languages.
Organizations : that discover information has a strategic value; they utilize their database systems
to gain an edge over their competitors.
The Database Model
A data model describes a way to structure and manipulate the data in a database. The structural part of
the model specifies how data should be represented(such as tree, tables, and so on ).The manipulative part
of the model specifies the operation with which to add, delete, display, maintain, print, search, select, sort
and update the data.
Distributed Database
Similarly , a distributed database is one in which different parts of the database reside on physically