DBMS - Data Independence

 

DBMS - Data Independence

A database system usually contains a lot of data in addition to 

users'data.Easily to locate and control the data. It is difficult to

 modify or update a set of metadata,

If the database system is not multilevel, then making any changes to the database system becomes difficult. Database systems are designed in multi-layers

The terms data Independence can be explained easily with the three schema architecture as following

data Independence can be defined as the capacity to change the schema at one level of a database system without having to change the schema at the next higher level.

The two types of data Independence are

1 logical data independence

2 physical data independence

logical data

logical data independence it is the capacity to change the conceptual schema without have to change external schema or applications program the conceptual schema can be changed to expand the database or to reduce the database. Intel letter case external schema that refer only to the remaining data should not be affected.

Student

Name	Student number	Class	major
Naresh	12	1	Cs
Amit	17	2	cs

Course

Course name	Course number	Credit hours	department
Computer	C-1201	2	C
DATA	C-1202	4	D
SCIENCE	C-1203	2	S
ENGLISH	C-100	1	E

SECTION

SECTION IDENTI	COURSE NUMBER	SEMESTER	YEAR	INSTRUCTOR
50	C-1201	PASS	2014	MOHAN
62	C-1202	FALL	2014	HAMENT
20	C-1202	FALL	2014	SWAMI
40	C-100	FALL	2014	KERMAN

Physical data Independence-

it is the capacity of change the internal schema without having to change the conceptual to external schema .changs to the internal schema may be needed because some physical files had to recognized- for example why creating additional access structure to improve the performance of retrieval or update . if the same data as before remains in the database we should not have to change the conceptual schema.

Student

Name	Student number	Class	major
Naresh	12	1	Cs
Amit	17	2	cs

Course

Course name	Course number	Credit hours	department
Computer	C-1201	2	C
DATA	C-1202	4	D
SCIENCE	C-1203	2	S
ENGLISH	C-100	1	E

SECTION

SECTION IDENTI	COURSE NUMBER	SEMESTER	YEAR	INSTRUCTOR
50	C-1201	PASS	2014	MOHAN
62	C-1202	FALL	2014	HAMENT
20	C-1202	FALL	2014	SWAMI
40	C-100	FALL	2014	KERMAN

Important of data independence

Important of data independence whenever we have multiple level DBMS its catalog must be expanded to include information on how map requests and data among the various level the DBMS user additional softwares to accomplish these mapping why referring to the mapping information in the catalog. Data Independence is accomplished because when the scheme is changed at some level the schema at the next higher level remains unchanged. only the mapping between the two levels it is changed9 hence applications program referring to The high-level schema needs not be changed