1. 第四维(4D)：
第四维是由 Laurent Ribardière 开发的关系数据库管理系统和 IDE。 4D 可以作为服务器运行，以便多个客户端可以管理单个数据库。 4D 创建于 1984 年，1987 年为 Macintosh 稍微推迟了公开发布。它是一个具有集成数据库管理系统的应用程序开发环境。
2. 亚马逊简单数据库：
它是 Amazon 托管的简单数据库服务，数据存储在 Amazon Cloud 中。它是 Amazon 的网络服务，用于实时对结构化数据运行查询。这个数据库是由 Amazon.com 用 Erlang 编写的。它具有以下特点——高可用性和灵活性，很少或没有管理负担。
4D 和 Amazon SimpleDB 的区别：
| S.No. | 4D | Amazon SimpleDB |
|---|---|---|
| 1. | It is developed By 4D, Inc in 1984. | It is developed By Amazon in 2007. |
| 2. | It is an application development environment with integrated database management system. | It is hosted simple database service by Amazon, with data stored in Amazon Cloud. |
| 3. | It supports PHP as programming languages. | The programming languages supported are .Net, C, C++, Erlang, Java, PHP, Python, Ruby, and Scala. |
| 4. | Server operating systems for 4D are OS X and Windows. | In Amazon SimpleDB, Hosted server operating systems. |
| 5. | Its primary database model is Relational DBMS. | Its primary database model is Key-value store. |
| 6. | It supports Server-side scripting. | It does not support Server-side scripting. |
| 7. | It is not available as cloud service. | It is available as cloud service. |
| 8. | It supports SQL query language. | It does not support SQL query language. |
| 9. | It supports only one replication method – Master-master replication. | It support replication methods. |
| 10. | 4D provides concept of Referential Integrity. Hence, there is Foreign Keys. | It does not provides concept of Referential Integrity. Hence, no Foreign Keys. |
| 11. | It supports ACID property. | It does not support ACID property. |
| 12. | Immediate Consistency is used to ensure consistency in distributed system. | Eventual Consistency and Immediate Consistency are used to ensure consistency in distributed system. |