ppt on dbms day 3

8/9/2019 PPT ON Dbms day 3

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Data ModelData Model

y Data Model is a collection of concepts

that can be used to describe the structure

of a data base.

y It provides the necessary means to

achieve data abstraction.(Hiding details of

data storage that are not needed by most

database users.)


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Structure of databaseStructure of database

y Structure means data types, relationships,

and constraints that should hold for the

data.


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SchemaSchema

y The description of data base is called

database schema.

y Description of data at some level.

y Each level has its own schema

y It is specified during database design and

is not expected to change frequently.

y A displayed schema is called schema

diagram.


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InstanceInstance

y The data in the database at a particular

moment in time is called a database state

or snapshot.

y It is also called instance.


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3 level architecture of data base3 level architecture of data base

Concerned with three forms of schemas:

y Physical,

y

Conceptualy External.


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Physical Data level schemaPhysical Data level schema

y The physical schema describes details

of how data is stored: files, indices, etc. on

the random access disk system.

y It also typically describes the record

layout of files and type of files.


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Conceptual Data LevelConceptual Data Level

y Hides details of the physical level.

y In the relational model, the conceptual

schema presents data as a set of tables

y Physical schema can be changed without

changing application:

y DBMS must change mapping from

conceptual to physical.


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External Data LevelExternal Data Level

y An external schema specifies a view of

the data in terms of the conceptual level.

y It is tailored to the needs of a particular

category of users.

y Portions of stored data should not be

seen by some users and begins to

implement a level of security andsimplifies the view for these users


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Data IndependenceData Independence

y Capacity to change the schema at one

level of a database system without having

to change the schema at next higher level.


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Types of Data IndependenceTypes of Data Independence

y Logical Data base independence

y Physical database independence


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Logical database independenceLogical database independence

y It is the capacity to change the conceptual

schema without having to change external

schemas.

y We can add more records or data type in

database without affecting end user or

external schema.


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Physical data independencePhysical data independence

y It is the capacity to change the internal

schema( physical level) without having to

change the conceptual schema.

y Here changes made to storage media, or

new structure of table is created will not

affect external and logical schema.


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DBMS LanguageDBMS Language

y Data definition language

y Data manipulation language

y Data control language

ppt on dbms day 3

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