Three Schema Architecture With Example In DBMS

Three Schema Architecture With Example In DBMS, Explain Three Schema Architecture Levels With Examples & Explanations

Where ANSI-SPARC stands for American National Standards Institute, Standards Planning And Requirements Committee.

The three-schema architecture is a convenient tool for the user to visualize the schema levels in a database system.

In this architecture, schemas can be defined at the following three levels:
Internal schema/Physical schema
Conceptual schema
External schema

The internal level has an internal schema, which describes the physical storage structure of the database.

The conceptual level has a conceptual schema, which describes the structure of the whole database for a community of users. The conceptual schema hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints.

 The external or view level includes a number of external schemas or user views.

The processes of transforming requests and results between levels are called mappings.


Example: university database

Physical schema:
Relations stored as unordered files.
Index on first column of students

Conceptual schema:
Student (sid: string, name: string, age: number, percent: real)
Courses (cid: string, cname: string, credits: number)
Enrolled (sid: string, cid: string, grade: string)

External schema:
Course_info(cid: string, enrollment: integer)

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