There are three main types of database schema:
- Physical schema: The physical schema is the lowest level of the database schema hierarchy and describes the physical organization of the data on the storage media. It specifies how the data is stored on the storage media and how the data is accessed.
- Logical schema: The logical schema is the next level of the database schema hierarchy and describes the logical structure of the data. It specifies the relationships between the different data elements and the constraints on the data.
- Conceptual schema: The conceptual schema is the highest level of the database schema hierarchy and describes the overall logical structure of the database. It is an abstract representation of the entire database and is independent of the physical representation of the data.
The physical schema is the most detailed level of the database schema and is concerned with the physical storage and organization of the data. The logical schema is a more abstract representation of the data and describes the relationships between different data elements. The conceptual schema is the most abstract level of the database schema and provides a high-level view of the entire database.
The database schema is important because it defines the structure and organization of the data in the database and helps to ensure the integrity and consistency of the data. It also serves as a blueprint for the design and development of the database and helps users to understand how the data is organized and how to access and manipulate it.