In this article, we are going to learn about an architecture for database systems called the three-level/schema architecture that helps achieve the characteristics of the database approach.
With the help of three schema architecture, we will also learn the concept of data independence.
DBMS Three Level Architecture Diagram
- The goal of these three schema/level architecture is to separate the user applications and physical database.
- The user application is at the topmost level of the database system.
- And the physical database is at the lowest level.
The database schemas are represented in 3 levels
- The first level is the Internal level.
- The Second level is the Conceptual level.
- The first level is the External level.
1. Internal Level
- This internal level has an internal schema and this schema describes the physical storage structure of the database.
- This internal schema uses one of the categories of data models that is the low level or the physical data models.
- It uses that physical data model to describe complete details of how data is stored and the access paths for the database.
2. Conceptual Level
- This describes the structure of the database.
- This schema hides the details of the physical storage structure of the database and concentrates or focuses more on describing entities, data types, relationships, constraints, attributes.
- So that is about the conceptual level.
3. External Level
- The topmost level that we have in our three schema architecture is the external level.
- The external level has several external schemas or external views and each external schema describes the part of the database that a user is interested in and hides the rest of the database from the user group.
- An external schema or view contains only that data which a user group is interested in and hides the remaining database from that particular user group.
- so this level has a view for each user group.
- so this is about the three levels and because it has three levels it is called three schema architecture here in the three schema architecture each user refers to its external schema so any request specified in the external schema is sent to the conceptual schema by the DBMS and further that request is sent to the internal schema for processing
- if the request from the user is the retrieval of data from the database then data is extracted from the stored database this process of transforming requests and results between these three levels is called mapping.
To conclude, The three schema architecture breaks the database down into three different categories, describes the structure of a specific database system, and the three schema architecture is used to separate the user applications and physical database.