Introduction to database abstraction and different levels of database abstraction

1. DATABASE
ABSTRACTION
Presented by:
Dr.Ritu Bhargava
Sophia Girls’College(Autonomous)
Ajmer

2. DATABASE ABSTRACTION
• The major purpose of a database system is to provide users
with an abstract view of the system. The system hides
certain details of how data is stored and created and
maintained
• Complexity should be hidden from database users.
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3. The data in DBMS is described at three levels
of abstraction:
1) Internal or physical level
2)Conceptual level
3)External level
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5. INTERNAL LEVEL
• At the internal or physical level,Students are
represented by a stored record type called
STORED-STU ,which is a 74 character long.
• Student record contains 4 fields or data items.
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6. 6
STORED-STU record length 74
SID 4 INTEGER OFFSET 0 UNIQUE
SNAME STRING LENGTH 20 OFFSET 0
SMAJOR STRING LENGTH 40 OFFSET 64
SCREDIT DEC 5,2 OFFSET 69

7. • INTERNAL LEVEL is the physical representation of the
database .
• This is the lowest abstraction of database.
• This level indicates HOW the data will be stored on the
Database and describes the data structure,file structure and
access methods to be used by the database.
• The internal schema defines the stored record ,methods of
representing data, indexing,data compression and
encryption techniques.
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8. CONCEPTUAL LEVEL
STORED-STU record length 69
SID : INTEGER (4)
SNAME :STRING (20)
SMAJOR :STRING (40)
SCREDIT: DEC ( 5,2)
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9. • At the conceptual level,the database contains information
concerning an entity type called STUDENT
• Each individual student has a SID,SNAME,SMAJOR,SCREDIT
• All the Database entities and relationships are included in this
databse abstraction .
• It descibes WHAT data is stored in the database and the
relationships among the data
• IT contains the logical structure of entire databse and seen by
DBA.
• It applies constraints on the data,has semantic information
about the data,checks to retain data consistency and
integrity,security information.
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10. EXTERNAL LEVEL
USER VIEW 1 USER VIEW2
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11. • EXTERNAL LEVEL is the user’s view of the database.
• This level is the highest level of abstraction .
• This level describes that part of database which is relevant to the
users.
• Any number of user views, may exist for a given conceptual or
global view of the database.
• It includes only those entities, attributes ,relationships in the real
world that is user is interested in. Other may be present in
database but user is not aware of it.
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12. • In the external level, different views may have different
representation on the same data.
• Some view include derived or calculculated data i.e data is
not stored in the database ,but are related when needed .
• This schema consists of the defination of the logical
records and the relationships in the external view.
• The external Schema is written using external DDL.
• It also contains the method of deriving objects in the view
from the objects in conceptual level.
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13. THANK YOU