Database Management Systems (dbms)

External Level

The data what user wants (Only selected parts of selected records from base table)
Base Table (Conceptual View)
View Table (External View)

Mapping

External/Conceptual mapping

• Define the correspondence between a particular external view and conceptual view.
• This specified how a particular external schema is derived from conceptual schema

Conceptual/Internal mapping

• Define the correspondence between the conceptual view and stored database.
• This specifies how the conceptual schema is represented at the internal level.
• If the structure of the stored database is changed, the conceptual internal mapping must also be changed accordingly.

Mapping..

Sno FName LName
Struct STAFF { int Staff_No; int Branch_No; char FName[15]; char LName[15]; date date_of_birth};
Staff_No LName Bno
Staff_No FName LName DOB Batch_no
External view 1
External view 2
Conceptual Level
Internal (Physical) Level
External Level

Data Independence

The major objective for the three-level architecture is to provide data independence

Logical Data Independence

Capacity to change the conceptual schema without having to change external schemas or application program.

Physical Data Independence

The ability to modify the physical schema without changing the conceptual (or external ) schema

Database Design

Database Design

The database design process can be broken down into four phases.

• Requirements collection and analysis phase
• Conceptual Design
• Logical Design
• Physical Design

Requirements collection and analysis phase

Prospective database users are interviewed to understand and document their data requirements