Sunday, July 18, 2021
Three schema Architecture
DBMS Three schema Architecture
- Internal Level
- Conceptual Level
- External Level
Three schema Architecture
- Three schema architecture is also called ANSI / SPARC architecture or three-level architecture.
- This framework is used to describe the structure of a specific database system.
- The three schema architecture is also used to separate user applications and physical databases.
- There are three levels in the three schema architecture. It breaks the database into three different categories.
The three-schema architecture is as follows:
In the above diagram:
- It shows the DBMS architecture.
- Mapping is used to convert request and response between different database levels of the architecture.
- Mapping is not good for small DBMS as it takes more time.
- External / conceptual mapping, it is necessary to convert the link from the external level to the conceptual schema.
- Conceptual / internal mapping converts DBMS requests from conceptual to internal level.
1. Internal Level
- This level contains an internal schema that describes the physical storage structure of the database.
- Internal schema is also known as physical schema.
- It uses the physical data model. It is used to define how the data will be stored in the block.
- Physical level is used to describe complex low level data structures in detail.
2. Conceptual Level
- Conceptual schema describes the design of a database at the conceptual level. The conceptual level is also known as the logical level.
- This schema describes the structure of the entire database.
- Conceptual level tells what data will be stored in the database and also tells what are the relationships between those data.
- In the conceptual level, the internal details such as the structure of the data implementation are hidden.
- Programmers and database administrators are working on such level.
3. External Level
- At the external level, a database consists of several schemas which are sometimes called subschemas. Subschema is used to describe different views of the database.
- External schema is also known as view schema.
- A view schema describes the database portion that a particular user group is interested in and hides the remaining databases from that user group.
- The View schema describes the end user interaction with the database system.