Date post: | 30-May-2018 |
Category: |
Documents |
Upload: | rohit-chaudhary |
View: | 215 times |
Download: | 0 times |
of 14
8/9/2019 PPT ON Dbms day 3
1/14
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.)
8/9/2019 PPT ON Dbms day 3
2/14
Structure of databaseStructure of database
y Structure means data types, relationships,
and constraints that should hold for the
data.
8/9/2019 PPT ON Dbms day 3
3/14
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.
8/9/2019 PPT ON Dbms day 3
4/14
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.
8/9/2019 PPT ON Dbms day 3
5/14
3 level architecture of data base3 level architecture of data base
Concerned with three forms of schemas:
y Physical,
y
Conceptualy External.
8/9/2019 PPT ON Dbms day 3
6/14
8/9/2019 PPT ON Dbms day 3
7/14
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.
8/9/2019 PPT ON Dbms day 3
8/14
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.
8/9/2019 PPT ON Dbms day 3
9/14
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
8/9/2019 PPT ON Dbms day 3
10/14
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.
8/9/2019 PPT ON Dbms day 3
11/14
Types of Data IndependenceTypes of Data Independence
y Logical Data base independence
y Physical database independence
8/9/2019 PPT ON Dbms day 3
12/14
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.
8/9/2019 PPT ON Dbms day 3
13/14
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.
8/9/2019 PPT ON Dbms day 3
14/14
DBMS LanguageDBMS Language
y Data definition language
y Data manipulation language
y Data control language