Database Architecture Part 2-Distributive Data Systems-Lecture Slides, Slides of Distributed Database Management Systems

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Conceptual Schema

Contains Semantic information about the data meaning, security and integrity information

Conceptual Schema

Relatively constant: designed with the present as well as future needs of an organization

Level 3 Internal or

Physical View

Concerns about the physical implementation of the database

Internal View

DBMS chooses type of data structures

lays out data on storage devices with operating system access methods

Physical Level

Generally same as Internal

Actual representation of data on the storage device

In the binary format

OS responsibility

Inter-Schema Mappings

Also a part of 3-level architecture External/conceptual mapping Conceptual/Internal

Con/Int Mapping

Specifies mapping between objects in the logical model to those in the physical model- data independence

3-Level Architecture

External Level Conceptual Level Internal Level Physical Data Organization Ext/Con Mapping View 1 View 2 View n Conceptual Schema Internal Schema Database User 1 (^) User 2 User n Con/Int Mapping

Data

Independence

Data Independence

A major outcome of 3-L Arch

The immunity of applications to change in storage structure and access strategy

Data Independence

Types

• Logical Data Independence
• Physical Data Independence

Logical Data

Independence

Changes in conceptual model do not affect the external views

Immunity of external level from changes at conceptual level

Physical Data

Independence

Changes in the internal model do not affect the conceptual model Immunity of Conceptual level from changes at Internal level

Changes Examples

Changing file organization

Index implementation, hash, tree etc.

Changing storage medium