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DATABASE Three-Level Architecture, DATA INDEPENDANCE - Coggle Diagram
DATABASE Three-Level Architecture
EXTERNAL LEVEL
is what the USER SEES
Example of a student view of the database is MyInfo
CONCEPTUAL LEVEL
Contains the LOGICAL STRUCTURE of the DATABASE
Such as...
ENTITIES
CONSTRAINTS
SEMANTIC INFORMATION
SECURITY INFORMATION
INTERNAL LEVEL
is the Physical DATABASE
Such as
PHYSICAL IMPLEMENTATION of Database
DBMS
HARDWARE
Purpose of Database 3LA
Separate each user's view of the database from the way its physically represented
User only see relavant data from database
DBA can change the database structures without affecting the user's view
Internal Structure is unaffected by changes to the physical changes such as storage or new device
DBA can make change to the conceptual structure of the database without affecting all users
DATA INDEPENDANCE
LOGIAL DATA INDEPENDENCE
EXTERNAL SCHEMAS are immune to the changes in the CONCEPTUAL SCHEMA
Example is changes to the ENTITIES, ATTRIBUTES & RELATIONSHIPS
PHYSICAL DATA INDEPENDENCE
CONCEPTUAL SCHEMA is immune to changes in the INTERNAL SCHEMA
Examples are changes to STORAGE DEVICES or FILE ORGANISATIONS