DBMS
a.
Data:
·
It is a collection of information.
·
The facts that can be recorded and which have implicit meaning known as
'data'.
·
Example:
Customer ----- 1.cname.
2.cno.
3.ccity.
b.
Database:
·
It is a collection of interrelated data.
·
These can be stored in the form of tables.
·
A database can be of any size and varying complexity.
·
A database may be generated and manipulated manually or it may be
computerized.
·
Example:
Customer
database consists the fields as cname, cno, and ccity
Cname
|
Cno
|
Ccity
|
c.
Database System:
1.What
are the advantages of a database system over conventional file processing
systems? (8
Marks, April-2000)
·
It is computerized system, whose overall purpose is to maintain the
information and to make that the information is available on demand.
·
Advantages:
1.Redundency can be reduced.
2.Inconsistency
can be avoided.
3.Data
can be shared.
4.Standards
can be enforced.
5.Security
restrictions can be applied.
6.Integrity
can be maintained.
7.Data
gathering can be possible.
8.Requirements
can be balanced.
d.
Database Management System (DBMS):
1.What
are the advantages of DBMS over File processing systems?
File
Processing System:
·
It is a collection of interrelated data and programs to access the
data.
·
It is a collection of programs that enables users to create and
maintain a database.
·
It is a 'General Purpose Software System’ that facilitates the
processes of Defining, Constructing and Manipulating databases for various
applications.
·
Advantages:
1.Data Independence
2.Efficient Data Access.
3.Data Integrity and security.
4.Data administration.
5.Concurrent access and Crash recovery.
6.Reduced Application Development Time.
·
Dis-advantages:
1.Data Redundancy.
2.Data Inconsistency.
3.Difficulty in accessing the data.
4.Data Isolation.
5.Security Problems.
LEVELS OF DATA ABSTRACTION
This is also called as 'The Three-Schema
Architecture’, which can be used to separate the user applications and the
physical database.
This is also called as 'The Three-Schema Architecture’, which can be used to separate the user applications and the physical database.
1.Physical
Level:
·
This is a lowest level, which describes how the data is actually
stores.
·
Example:
Customer
account database can be described.
2.Logical Level:
·
This is next higher level that describes what data and what
relationships in the database.
·
Example:
Each record
type customer = record
cust_name:
sting;
cust_city: string;
cust_street: string;
end;
3.Conceptual (view) Level:
·
This is a lowest level, which describes entire database.
·
Example:
All
application programs.
DATA
MODELS
·
The entire structure of a database can be described using a data model.
·
A data model is a collection of conceptual tools for describing
·
Data models can be classified into following types.
1.Object Based Logical Models.
2.Record Based Logical Models.
3.Physical Models.
Explanation
is as below.
1.Object Based Logical Models:
·
These models can be used in describing the data at the logical and view
levels.
·
These models are having flexible structuring capabilities classified
into following types.
a. The entity-relationship
model.
b. The object-oriented model.
c. The semantic data model.
d. The functional data model.
2.Record Based Logical
Models:
·
These models can also be used in describing the data at the logical and
view levels.
·
These models can be used for both to specify the overall logical
structure of the database and a higher-level description.
·
These models can be classified into,
1. Relational model.
2. Network model.
3. Hierarchal model.
3. Physical Models:
·
These models can be used in describing the data at the lowest level,
i.e. physical level.
·
These models can be classified into
a. Unifying model
b. Frame memory model
.
5.Entity Relational Model
(E-R Model)
The E-R model can be used
to describe the data involved in a real world enterprise in terms of objects
and their relationships.
Uses:
·
These models can be used in database design.
·
It provides useful concepts that allow us to move from an informal
description to precise description.
·
This model was developed to facilitate database design by allowing the
specification of overall logical structure of a database.
·
It is extremely useful in mapping the meanings and interactions of real
world enterprises onto a conceptual schema.
·
These models can be used for the conceptual design of database
applications.
