There are a number of principles that guide the design of ORM systems:
* Simplicity: ORMs should be easy to use and understand, even for developers who are not familiar with relational databases.
* Transparency: ORMs should not hide the underlying relational database from the developer. Developers should be able to see and understand the SQL queries that are being generated by the ORM.
* Performance: ORMs should not significantly impact the performance of your application.
* Extensibility: ORMs should be extensible, so that you can customize them to meet your specific needs.
Some of the most popular ORM tools include:
* ActiveRecord: ActiveRecord is an ORM for Ruby that is based on the Active Record pattern.
* Django ORM: The Django ORM is an ORM for Python that is included with the Django web framework.
* Entity Framework: Entity Framework is an ORM for .NET that is included with the .NET Framework.
* Hibernate: Hibernate is an ORM for Java that is based on the Java Persistence API (JPA).
ORM systems can be a powerful tool for developing applications that interact with relational databases. By following the principles of simplicity, transparency, performance, and extensibility, you can create ORMs that are easy to use, understand, and maintain.