Database abstraction

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. 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

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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. 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 S-NAME S-CREDIT SID S-NAME S-CREDIT

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