The document discusses the three levels of abstraction in a database management system: the internal, conceptual, and external levels. The internal level describes the physical representation and storage of data. The conceptual level defines the logical structure and relationships of data in the database. The external level describes different views of the data that are relevant to users but hides implementation details.

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.
2

3. The data in DBMS is described at three levels
of abstraction:
1) Internal or physical level
2)Conceptual level
3)External level
3

4. 4

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.
5

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.
7

8. CONCEPTUAL LEVEL
STORED-STU record length 69
SID : INTEGER (4)
SNAME :STRING (20)
SMAJOR :STRING (40)
SCREDIT: DEC ( 5,2)
8

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.
9

10. EXTERNAL LEVEL
USER VIEW 1 USER VIEW2
10

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.
11

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.
12

13. THANK YOU