10-02-2012, 03:44 PM
INTRODUCTION TO DATABASE MANAGEMENT SYSTEMS
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Introduction
A database consists of four elements as given,
i) Data
ii) Relationships
iii) Constraints
iv) Schema
i) Data
Data are binary computer representations of stored logical entities.
Software is divided into two general categories-data and programs.
A program is a collection of instruction for manipulating data.
Data exist is various forms- as numbers tents on pieces of paper, as bits and bytes stored in electronic memory or as facts stored in a persons mind.
ii) Relationships
Relationships explain the correspondence between various data elements.
iii) Constraints
Are predicates that define correct database states.
iv) Scheme
Schema describes the organization of data and relationships within the database.
Schema defines various views of the database for the use of various system components of the database management system and for the application’s security.
A schema separates physical aspects of data storage form the logical aspects of data representation.
Types of schema
a) Internal schema: defines how and where the data are organized in physical data storage.
b) Conceptual schema: defines the stored data structures in terms of the database model used.
c) External schema: defines a view (or) views of the database for particular uses.
In database management systems data files are the files that store the database information whereas offer files, such as index files and data dictionaries, store administrative information known as metadata.
Data base are organized by fields, records and files.
i) Fields: is a single piece of information.
ii) Record: is one complete set of fields.
iii) File: is a collection of records.
