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Transcript of CHAP2 Three Level Architecture.pdf
7/26/2019 CHAP2 Three Level Architecture.pdf
http://slidepdf.com/reader/full/chap2-three-level-architecturepdf 1/20
Architecture of DatabaseManagement System
ByDr. Parteek Bhatia
Assistant ProfessorDepartment of Computer Science &
EngineeringThapar University
Patiala
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Early Two Level Architecture
Early proposal for a standard terminology and
general architecture for database systemswas produced in 1971 by the DBTG (Data
Base Task Group)
Appointed by the Conference on DataSystems and Languages (CODASYL, 1971).
Recommend two level approach.
Simplified Approach To DBMSBy Parteek Bhatia
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Early Two Level Architecture
Contd..
Schema
Subschema
Simplified Approach To DBMSBy Parteek Bhatia
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ANSI Three Level Architecture
External Level
Conceptual Level
Internal Level
Simplified Approach To DBMSBy Parteek Bhatia
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Three Level Architecture
Simplified Approach To DBMSBy Parteek Bhatia
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External Level or View level
It is the users’ view of the database. This
level describes that part of the database thatis relevant to each user.
,form (day, month, year), while another may
view dates as (year, month, day).
Simplified Approach To DBMSBy Parteek Bhatia
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Conceptual Level or Logical level
It is the community view of the database. This
level describes what data is stored in thedatabase and the relationships among the data.
All entities, their attributes, and theirrelationships;
The constraints on the data;
Security and integrity information.
Simplified Approach To DBMSBy Parteek Bhatia
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Internal Level or Storage level
It is the physical representation of the
database on the computer. This leveldescribes how the data is stored in thedatabase.
Simplified Approach To DBMSBy Parteek Bhatia
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Internal Level or Storage level
The internal level is concerned with:
Storage space allocation for data and
indexes;
Record descriptions for storage;
Record placement;
Data compression and data encryptiontechniques.
Simplified Approach To DBMSBy Parteek Bhatia
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Schema
The overall description of the database is
called the Database Schema.
A schema is defined as an outline or a plan
existing at the particular level.
The schema is sometimes called the
intension of the database, while an instanceis called an extension (or state) of thedatabase.
Simplified Approach To DBMSBy Parteek Bhatia
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Example
Simplified Approach To DBMSBy Parteek Bhatia
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Mapping between Views
External/Conceptual Mapping
A mapping between the external and
conceptual views gives the correspondence
the external and conceptual views.
Simplified Approach To DBMSBy Parteek Bhatia
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Conceptual/Internal Mapping
Conceptual schema is related to the internal
schema by the conceptual/internal mapping.This enables the DBMS to find the actualrecord or combination of records in h sical
storage that constitute a logical record inconceptual schema.
Simplified Approach To DBMSBy Parteek Bhatia
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Data Independence-Achievement
of Layered Architecture of DBMSTwo kinds of data independence:
Logical data independence
Ph sical data inde endence
Simplified Approach To DBMSBy Parteek Bhatia
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Logical data independence
Logical data independence indicates that the
conceptual schema can be changed withoutaffecting the existing external schemas.
Simplified Approach To DBMSBy Parteek Bhatia
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Physical data independence
Physical data independence indicates that
the physical storage structures or devicescould be changed without affectingconce tual schema.
Simplified Approach To DBMSBy Parteek Bhatia
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Procedure for Database Access
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Metadata or Data Dictionary
A metadata (also called the data
dictionary) is the data about the data. Data dictionary may be either active or
passive. An active data dictionary (also
managed automatically by the databasemanagement software.
The passive data dictionary (also called
non-integrated data dictionary) is the oneused only for documentation purposes.
Simplified Approach To DBMSBy Parteek Bhatia
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Components of a DBMS
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References
Simplified Approach to DBMS
By
Parteek Bhatia, Kalyani Publisher
Simplified Approach To DBMSBy Parteek Bhatia