Lecture-3 DBMS Architecture.pptx

dbms answer

1. Department of Information Technology Jagannath International Management School Vasant Kunj , New Delhi - 110070 (Affiliated to Guru Gobind Singh Indraprastha University, New Delhi) Recognized u/s 2(f) by UGC & Accredited with ‘A’ Grade by NAAC Participant of UNGC & UNPRME, New York ISO 9001:2015 Quality Certified Subject Name : Database Management Systems (DBMS) Subject Code: BCA-108 Created By: Dr. Meenakshi Narula

2. Subject: DBMS Lecture-3 Topic: DBMS Architecture & Data Independence

3. List of Topics DBMS Schema and Instance DBMS Architecture Data Independence

4. Schemas, Instances and Database State Database Schema (meta-data): The Design of a database is called the schema. It Includes descriptions of the database structure and the constraints that should hold on the database. The database schema changes very infrequently. Database Instance : The actual data stored in a database at a particular moment in time . Also called database state ( or occurrence, snapshot) The database state changes every time the database is updated. Schema is also called intension , whereas state is called extension.

5. Schema diagram for UNIVERSITY database schema construct

6. Instance diagram for UNIVERSITY database

7. DBMS Architecture External schema at the external level to describe the various user views . Usually uses the same data model as the conceptual level or high-level data model. Conceptual schema at the conceptual level to describe the structure and constraints for the whole database. Uses a conceptual or an implementation data model. Internal schema at the internal level to describe data storage structures and access paths . Typically uses a physical data model. Three-Schema Architecture

8. The Three-schema architecture 2-6

9. The External or View Level Schema Each end users’ view of the data environment Modeler subdivides requirements and constraints into functional (Business unit’s) modules

10. External Schema – Advantages Easy to identify specific data Facilitates designer’s job Creation of external models Simplifies application program development

11. The Conceptual or Logical Level Schema (1 of 2) Global view of the entire database Representation of data for the entire organization

12. The Conceptual Level Schema (2 of 2) Software and hardware independent Most widely used conceptual model is the Entity Relationship (ER) model

13. The Internal or Physical Level Schema The database as “seen” by the DBMS Maps the conceptual model to the DBMS Depicts a specific representation of an internal model Logical independence

14. Three Schema Architecture – Advantages Database abstraction Easier to use for a user. Allows each user to access customized view of data. Enables a database admin to change the storage structure without affecting the user’s view

15. Data Independence The capacity to change the schema at one level without having to change the schema at the next higher level Types: Logical Data Independence : The capacity to change the conceptual schema without having to change the external schemas and their application programs. Physical Data Independence : The capacity to change the internal schema without having to change the conceptual schema. Requires only the mappings between one schema and higher-lever schemas to change

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