What is Database Schema?
A database schema is a structure that describes the organization of data in a database. It specifies the tables, fields, relationships, and other elements that make up the database, and defines how the data is stored and accessed.
A database schema can be represented visually using a diagram called an Entity Relationship Diagram (ERD). An ERD shows the different entities in the database and the relationships between them. For example, an ERD for a database of employees might include entities for employees, departments, and projects, and show the relationships between these entities (e.g., an employee works in a department and is assigned to one or more projects).
There are several types of database schemas, including:
- Physical schema: This is the actual organization of data in the database, including the data types, sizes, and other characteristics of the fields.
- Logical schema: This is the organization of data as it is perceived by the user. It describes the relationships and meanings of the data, but not the physical details of how it is stored.
- View schema: This is a virtual representation of the data, created by selecting and combining data from multiple tables or views.
The database schema is an important part of the database design process, as it determines how the data is stored and accessed. A well-designed schema can make it easier to use and maintain the database, while a poorly designed schema can lead to problems such as data redundancy, inconsistencies, and poor performance.