Database abstraction

Database abstraction

• 1.
  DATABASE ABSTRACTION Presented by: Dr.Ritu Bhargava SophiaGirls’College(Autonomous) Ajmer
• 2.
  DATABASE ABSTRACTION • Themajor 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 inDBMS is described at three levels of abstraction: 1) Internal or physical level 2)Conceptual level 3)External level 3
• 4.
  4
• 5.
  INTERNAL LEVEL • Atthe 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 length74 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 LEVELis 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 recordlength 69 SID : INTEGER (4) SNAME :STRING (20) SMAJOR :STRING (40) SCREDIT: DEC ( 5,2) 8
• 9.
  • At theconceptual 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 VIEW1 USER VIEW2 10
• 11.
  • EXTERNAL LEVELis 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 theexternal 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