DBMS
Data
Data is a valuable asset for an organization. Data is
generally thought to be numbers and text. In addition data also includes
multimedia files such as an image, audio files, video clips etc.
Information
Information is the manipulated and processed form of data.
Knowledge
Information organized and evaluated in the human's mind so
that it can be used purposefully is known as Knowledge.
Data Base
Data is a very valuable resource in the operation and
management of an organization. Database is a well organized collection of data
that are related in a meaningful way, which can be shared by multiple users but
stored only once.
Feature of data in database
- It should be well organized.
- It should be related
- It should be flexible to change.
- It should be recoverable in case of damage
- It should be stored permanently
- It should be shared among different users as well as applications.
Operations performed on the database
- Insertion
- Updation
- Deletion
- Selection
Components of database system environment
- Data
- Hardware
- Software
- Users
Data : the data
act as bridge between the machine parts and the users which directly access it.
Data may be of different types
Userdata
Metadata
Application metadata
Hardware : The hardware consists of the secondary storage
devices such as magnetic disks, optical disks , magnetic tapes etc.
Software: The software part mainly consist of DBMS which
acts as a bridge between user and the database
Users: users are those persons who need information
from the database to carry out their primary business responsibilities.
Types of users
Database Administrator
Database Designers
End users
Application programmers
DBMS stand for Database Management System. DBMS is
basically a collection of programs that enable user to store, modify, extract
information from Database as per the requirements.
Advantages of DBMS
- Controlling data redundancy
- Elimination of inconsistency
- Better services to the users
- Flexibility of the system is improved
- Standards can be enforced
- Security can be improved
- Provide backup and recovery
Disadvantages of DBMS
- Increased complexity
- Confidentiality, privacy and security risk
- Threat to data quality and data integrity
- Complexity of backup and recovery
Schema
The overall design of the database is called schema. A
schema shows an overall structure into which the values of all data items are
fitted.
Sub schema
A subset of schema is called a sub schema. It inherits the
same properties as that of a schema
Instances.
The collection of information stored in the database at a
particular moment called instance.
DBMS Architecture
The DBMS architecture is a framework where the structure of
the DBMS is described. ANSI-SPARC (American Nationals Standards Institute-
Standards Planning and Requirements committee). THE ANSI-SPARC three level
architecture consists of the following three levels.
External level
Conceptual level
Internal level
External level : external level also known as individual user
view is the highest level of three level DBMS architecture. This level describe
the user's view of the database.in this level, only those portions of the
database are described that are relevant to the user or applications program
and hides the rest of the database details.
Conceptual level : the conceptual level sometimes known as logical level that
describe the logical structure of the whole database for user i.e. global view
of data. it is represented as the middle level in the three level architecture.
The conceptual view is defined by the conceptual schema which describe all the
database entities, attributes, and relationships together with constraints.
Internal level : the internal level is the lowest level of the
three level architecture of DBMS. This level describe how the data will be
stored and also describe the data structure and access method to be used by the
database.
Mapping between views
The three levels of DBMS architecture don't exist
independently of each other. There must be correspondence between the three
levels. This correspondence between different levels is known as Mapping.
Types of Mapping
- Conceptual/internal Mapping
- External/Conceptual Mapping
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