DBMS 1 Lesson 3

Today I’ll talk about Database Architecture with reference to ANSI/SPARC 3 level architecture for DB systems.

if You haven't studied Lessons posted earlier click below Links

Lesson 1,Lesson 2



Lesson 3:

External View(Virtual Tables)

• Level Closest to the user
• Describes DB view of one group of DB users
• Concerned with the way data is viewed by individual users
• Describes part of the DB to users whom it concerns & hide rest of the part from the users

Conceptual View

• Level between External and Internal
• Concern with the way the data is logically represented
• Describes structure of the whole DB for all the users

Internal View

• Level closest to the physical storage
• Concerned with the actual data storage
• Describes physical data storage structure of DB
• Uses physical data model and describes complete access path to DB

One of the main Advantage of using a DB is Data Independence.This concept is explained using 3 level architecture.

Data Independence: Capacity to change the schema at one level of DB system without having to change the schema at the next higher level.

Data Independence is of 2 types

• Logical Data Independence
• Physical Data Independence

Logical Data Independence

1. Capacity to change conceptual schema without changing external schema
2. Can change table structure without changing external view of the table

Physical Data Independence

1. Capacity to change Internal schema without changing conceptual schema
2. File can be reorganize without changing table structures used to create it

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Next Lesson will be based on Normalization.Please keep in touch...