Updated: 07/31/2022 by Computer Hope
Illustrated rule book

A schema may refer to any of the following:

1. In general, a schema refers to any plan or vision that is a well-thought-out document with set rules and restrictions.

2. When referring to a database, a schema describes the structure and rules of a database and the relationships of data elements.

Example database schema

Here is a simple, non-scaling schema for users and their read/write permissions. It has three tables (tblUsers, tblPermissions, and tblUsersPermissions), with only a few columns in each. It defines two relationships (one-to-many from tblUsers to tblUsersPermissions, and one-to-many from tblPermissions to tblUsersPermissions), commonly shown in an ERD (entity relationship diagram) as 1 -> ∞.

Schema entity relationship diagram

Schema users table design

Schema permissions table design

Schema users-permissions table design

Using this database schema, data can be added to a database.

Schema data

Using SQL, you can retrieve a list of users and their permissions.

SELECT tblUsers.txtUser, tblPermissions.txtPermission
FROM tblUsers 
  INNER JOIN tblUsersPermissions ON tblUsers.tblUsersID = tblUsersPermissions.tblUsersID 
  INNER JOIN tblPermissions ON tblUsersPermissions.tblPermissionsID = tblPermissions.tblPermissionsID
ORDER BY tblUsers.txtUser, tblPermissions.txtPermission;

Schema query

3. When referring to an API, a schema is a formal definition of how data is properly transmitted to an API. It also dictates how the API will respond to the request.

Database, Database terms, Flowchart