A relational database schema is the tables, columns and relationships that make up a relational database. A schema is often depicted visually in modeling software such as ERwin or drawing software such as Viso.
The Purpose of a Schema
A relational database schema helps you to organize and understand the structure of a database. This is particularly useful when designing a new database, modifying an existing database to support more functionality, or building integration between databases.
Creating the Schema
There are two steps to creating a relational database schema: creating the logical schema and creating the physical schema. The logical schema depicts the structure of the database, showing the tables, columns and relationships with other tables in the database and can be created with modeling tools or spreadsheet and drawing software. The physical schema is created by actually generating the tables, columns and relationships in the relational database management software (RDBMS). Most modeling tools can automate the creation of the physical schema from the logical schema, but it can also be done by manually.
Modifying the Schema
The structure of a relational database will inevitably change over time as data needs change. It's just as important to document changes to your relational database schema as it was to document the original design, otherwise it becomes increasingly difficult to update or integrate the database. Be sure to save copies of previous configurations, so that changes can be removed if problems occur.